Implementing a Reference Measurement System for C-peptide: Successes and Lessons Learned

Abstract

Background

Assessment of endogenous insulin secretion by measuring C-peptide concentrations is widely accepted. Recent studies have shown that preservation of even small amounts of endogenous C-peptide production in patients with Type 1 diabetes reduces risks for diabetic complications. Harmonization of C-peptide results will facilitate comparison of data from different research studies and later among clinical laboratory results at different sites using different assay methods.

Content

This review provides an overview of the general process of harmonization and standardization and the challenges encountered with implementing a reference measurement system for C-peptide.

Summary

Efforts to harmonize C-peptide results are described including those by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)-led C-peptide Standardization Committee in the US, activities in Japan, efforts by the National Institute for Biological Standards and Control (NIBSC) in the UK, activities led by the Bureau International des Poids et Mesures (BIPM) and the National Metrology Institute in China (NIM China). A traceability scheme is proposed along with next steps for implementation. Suggestions are made for better collaboration in an effort to optimize the harmonization process for other measurands.

The need for accurate, traceable and comparable measurements for C-peptide

C-peptide is a proinsulin cleavage product released from the pancreas in amounts equimolar to insulin. Although C-peptide is co-secreted with insulin, its half-life is about 10 times longer than that of insulin (1). As a result, measurement of C-peptide can be used as a substitute marker for monitoring endogenous insulin production (2,3).

The Diabetes Control and Complications Trial showed that in subjects with type 1 diabetes higher C-peptide concentrations were associated with improved HbA1c, less hypoglycemia, and less retinopathy and nephropathy (4). Stabilization of C-peptide concentrations is therefore being used as a measurable endpoint for immunomodulatory trials in type 1 diabetes (5, 6). Some studies have also suggested that C-peptide is biologically active and may play a role in preventing and possibly reversing some chronic complications of type 1 diabetes (7-9). It is therefore important that C-peptide measurements be harmonized to a common reference in order to compare and interpret results across various clinical trials and other research studies.

The General Process of Harmonization/Standardization: Components of the Reference Measurement System

Harmonization/standardization can be achieved by calibration of all measurement procedures to be traceable to the same reference system. Different calibration hierarchies that can be implemented to achieve measurement traceability are described in the International Organization for Standardization (ISO) 17511:2003 standard (10). In principle, as C-peptide is a well-defined chemical entity, its concentration can be measured in SI units, with a traceability chain linking patient results from routine laboratory procedures, via commutable secondary reference materials (in serum) and reference measurement procedures to a primary reference material (pure substance) value assigned for the mass fraction of C-peptide in the material. This traceability would allow clinical results to be comparable across measurement systems, location, and time and is essential for patient care, research translation and disease prevention and control.

Establishing traceability for calibrator and control materials for in vitro diagnostic devices became mandatory in Europe with the implementation of the European Union Directive on in vitro diagnostic devices. Although this is a European Union Directive, it had a worldwide effect on clinical laboratory measurements since these devices have a worldwide market. The ISO standard 17511:2003 provides the framework for calibration traceability in laboratory medicine (10). There are also several reviews of the traceability process and examples of traceability chains for specific measurands (11-14).

The Joint Committee for Traceability in Laboratory Medicine (JCTLM) is an international committee created in 2002 by the Bureau International des Poids et Mesures (BIPM), International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and International Laboratory Accreditation Cooperation (15). The JCTLM has established a database containing lists of higher-order reference materials, higher-order reference measurement procedures and accredited reference laboratory services that have been reviewed and found to meet the requirements of the harmonized standards that support the in vitro diagnostics (IVD) Directive (16). The production and value assignment of reference materials, the development of reference measurement procedures and provision of reference measurement services may and often occurs in different laboratories. However, it is essential that these organizations work together so that each component of the traceability chain can be taken into account and traceability can be established throughout the reference system.

Efforts to harmonize C-peptide results

Activities Sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

In 2002, the NIDDK in the US organized a C-peptide standardization committee and funded an international comparison study of C-peptide assays. The Diabetes Diagnostic Laboratory (DDL) at the University of Missouri coordinated this effort. The goal of the initial studies was to assess the degree of equivalence of C-peptide results and to determine whether C-peptide results could be harmonized. The majority of C-peptide assays have been calibrated for many years with the pure World Health Organization (WHO) International Reference Reagent (IRR) for C-peptide (IRR 84/510) and yet these assays produced results that differed among measurement procedures (17). Additional off-line calibration with WHO IRR 84/510did not successfully improve equivalence of results. However, matrix-appropriate patient samples could successfully be used to calibrate assays and greatly reduce variability of results among methods (18). Samples for these studies were obtained with IRB approval from the University of Missouri Health Sciences. Anisotope dilution liquid chromatography mass spectrometry (ID-LC/MS)measurement procedure using a purified ¹³C, ¹⁵N-labeled reference standard had been described and was used to assign reference values to serum calibrators(19, 20).However, the pure reference standard was not developed into a certified reference material. Figure 1 shows the between-lab/between-method variability before and after calibration with serum based secondary reference material value-assigned by the ID-LC/MS reference measurement procedure.

Figure 1.

Between-lab/between-method variability before (A) and after (B) calibration with serum based secondary reference material with assigned values. Each symbol represents a different assay method. The solid line represents the reference measurement procedure results.

In 2008 the C-Peptide Committee initiated yearly meetings during the Annual Meeting of the American Association of Clinical Chemistry with manufacturers of C-peptide assays. In 2010, the group discussed the need to develop a suitable primary reference standard and all agreed that this was an important step. However, no standard became available over the next five years. The C-peptide committee agreed that it was important to move forward with harmonization and manufacturers agreed that the candidate reference measurement procedure should be internationally recognized by being listed on the JCTLM database. Following this recommendation, the ID-LC/MS candidate reference measurement procedure was established at a second site. A comparison study confirmed the equivalence of results from the two sites (20), and the reference measurement procedure was then listed in the JCTLM database in 2014, having been reviewed by the independent experts and found to be compliant with ISO 15193:2009 requirements (21).

By July 2014, the C-peptide committee had shown that variability among assay methods could be reduced by using serum-based secondary reference materials with values assigned by the JCTLM listed ID-LC/MS reference measurement procedure. Manufacturers were asked to begin the recalibration process and adjust their calibration to the matrix-appropriate secondary reference materials that had values traceable to the pure labeled C-peptide standard used to calibrate the ID-LC/MS reference measurement procedure. Since C-peptide is considered an exempt assay by the US Food and Drug Administration, manufacturers are not required to re-submit the entire assay with a new calibration in the US. Therefore, the timeframe for Food and Drug Administration approval of a recalibration is relatively short.

In 2015, it became clear that other efforts (discussed in more detail below) to standardize C-peptide measurements were on-going, in addition to the NIDDK C-peptide Standardization Committee's activities, and this would raise further issues to be solved before a global harmonization scheme could be implemented.

Activities of the BIPM and National Metrology Institute of China (NIM China)

National Metrology Institutes (NMIs) provide certified reference materials, develop reference measurement procedures and provide reference measurement services for many areas of chemical and biological measurement including Laboratory Medicine. In order to demonstrate the accuracy and equivalence of the measurement services and values assigned to reference materials, the NMIs participate in regular inter-laboratory comparisons, which are named key comparisons coordinated through the BIPM's Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM), and have the code CCQM-KXX, where the XX is a number identifying a particular comparison, with the results publicly available in the BIPM key comparison database (http://kcdb.bipm.org/). In 2014, the BIPM together with the NIM China, organized CCQM-K115, to compare NMI capabilities to measure the mass fraction of C-peptide in a pure C-peptide material. C-peptide was chosen as the material for the comparison for several reasons: it was a model system for mass fraction assignments of straight chain peptides with molar mass of less than 5000 g/mol; CRMs for C-peptide and reference measurement procedures for C-peptide measurement were already being provided by at least one NMI (NMIJ) and listed in the JCTLM database; the material would be available in sufficiently large quantities for it to be value-assigned by independent methods by the BIPM and NMIs, notably by mass balance, amino acid analysis corrected for peptide impurities, as well as quantitative NMR corrected for peptide impurity content. The CCQM-K115 material was purchased from a peptide material manufacturer and not purified further by the BIPM, as the material was being used to demonstrate measurement capability equivalence amongst NMIs, rather than being prepared as a very high purity calibration material; this enabled the BIPM to distribute 25 mg of material to each participant in the comparison. The homogeneity and stability of the material were studied at the BIPM, following ISO Guide 34 guidelines (22), and found to be suitable for a CCQM comparison. C-peptide as a solid material is a salt, and so in addition to the C-peptide component, it is expected to contain: counter ions; peptide impurities; and water. Ten NMIs participated in the key comparison. The reference value for the comparison was decided in the April 2016 meeting of the CCQM Protein Analysis Working Group, and was based on mass balance values of all impurities and their measurement uncertainties, allowing a key comparison reference value of 801.8 mg/g to be assigned with an expanded uncertainty of 6.2 mg/g (k=2). The BIPM identified and quantified over 70 peptide impurities in the material using high-resolution mass spectrometry. Amino acid analysis methods performed by the NMIs were in general found to agree with the reference value within their stated uncertainties, provided peptide impurities had been appropriately accounted for in the amino acid analysis, with expanded uncertainties of approximately 50 mg/g (k=2) for amino acid methods reported on this particular material(23). Beginning in 2017, NIM China will provide this material for use as a CRM.

Activities of the Japanese Committee for Clinical Laboratory Standards (JCCLS) and the National Metrology Institute of Japan (NMIJ)

An extensive standardization project for clinical chemistry in Japan was initiated by the JCCLS and the NMIJ under the support of the New Energy and Industrial Technology Development Organization in 2005-2007. The aim of this project was to establish traceability chains to higher order reference materials in the field of clinical chemistry in Japan. This large-scale project involved major Japanese IVD manufacturers, and provided the opportunity for a comparison study of results from different manufacturers' assays. More than twenty measurands were included in the project, with C-peptide as one of the analytes of interest, with seven manufacturers participating in the harmonization/standardization study. Although the pure C-peptide solution (prepared from WHO IRR 84/510 or a commercial reagent) had failed to harmonize kit results, the use of serum calibrators, prepared by spiking pure C-peptide material into C-peptide depleted serum, successfully reduced between-method variability. Calibrators prepared from patient serum were also shown to reduce variability to the same extent. (24) The project' send-point was a demonstration of harmonization. The project also succeeded in making Japanese manufacturers aware of the importance of higher-order reference materials for standardization.

The NMIJ initiated an effort to develop certified reference materials for proteins and peptides at the same time as the national project. In order to establish a certified reference material of C-peptide having traceability to SI, the NMIJ developed isotope-dilution mass spectrometry (IDMS) (25, 26) methods for amino acid analysis and amino acid certified reference materials (CRM)(27). The certification process of C-peptide candidate CRM consisted of impurity quantification, and homogeneity and stability testing. The concentration of C-peptide was determined by two independent amino acid analyses using liquid phase and gas phase hydrolyses. These analyses utilized IDMS with ¹³C and ¹⁵N labeled amino acids as internal standards and NMIJ CRMamino acids to enable SI-traceable measurements. This material is a high purity lyophilized synthetic peptide produced in compliance with ISO Guide 34 (28). The provision of the first lot was started in 2011, and the second lot, NMIJ CRM 6901-b, is now available.

The need for serum calibrators having traceability to higher-order reference material was widely recognized after the national project. The reference measurement procedure for serum C-peptide measurement using both IDMS and the pure C-peptide CRM made it possible to achieve traceable measurements for the value-assignment of the serum calibrator. However, to cover the reference interval of serum C-peptide, especially in the low concentration range, it was necessary to improve the sensitivity of LC/MS measurements. The combination of immunoaffinity purification and precolumn-derivatization using 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate was shown to result in a 20-fold improvement in sensitivity. The IDMS measurement was performed using C-peptide CRM 6901-b as the calibrant and ²H₈-Val₂ C-peptide as the internal standard by the double isotope dilution method. The method validation studies showed a linear response in the 0.003-2.9 ng intervalon the column which covered the reference interval. The relative standard deviation within and between days were both less than 4.0 %, and the results of spike and recovery experiments showed mean recoveries between 99 and 108%. The comparison study of serum C-peptide measurements between the IDMS and a chemiluminescence enzyme immunoassay by Lumipulse (Fujirebio)showed high correlation across theinterval examined [(0.06-2.81) nmol/L, r² = 0.999] (29). Both the C-peptide CRM and IDMS-based reference measurement procedureen abled traceable measurements of serum C-peptide, and both the material and the measurement procedure have been listed in the JCTLM database.

The NMIJ also participated in CCQM-K115 key comparison. The value submitted by NMIJ for the comparison, 808 mg/g (k=2) and an expanded uncertainty of 48 mg/g, agreed with the reference value(23). This provided confidence in the NMIJ value-assignment procedures, and value and measurement uncertainty on the much purer C-peptide material that NMIJ had issued as CRM 6901-b and is listed in the JCTLM database.

Activities of the National Institute of Biological Standards and Control (NIBSC) and the WHO

It is now well accepted that calibrators prepared in a sample matrix and value-assigned using a reference measurement procedure will be important in improving the between-method agreement of C-peptide measurements in patient samples. However, it was also recognized by the UK and the WHO in 2010, that having made a reference material available to manufacturers for nearly 30 years, and with no certainty that certified matrix-based reference materials for C-peptide in serum would be available in the near future, there was an ongoing responsibility to this community to maintain the availability of such a reference material for the continuing development, calibration and monitoring of C-peptide immunoassays. Since stocks of the existing WHO reference reagent (84/510) were exhausted, a timely replacement was therefore required and an international project was initiated. It should be added that it was not the intention of this project to prepare a material to be used as a primary standard to calibrate the ID-LC/MS reference measurement procedure. Indeed, any study to prepare a WHO reference material intended to be used to calibrate immunoassays is usually conducted very differently than one designed to produce a primary standard to calibrate a reference measurement procedure. For example, the reference material is typically lyophilized in glass ampoules in very low amounts and it is not designed to be weighed out of the ampoule. In addition, WHO International Standards are prepared in large batches and are thoroughly evaluated for their long-term stability and fitness for purpose in immunoassay systems. However, it was recognized by NIBSC and WHO that the anticipated uses of this material may change (e.g. from a primary calibrator for immunoassays to a stable external reference to monitor within-assay performance) once the complete reference measurement system (consisting of a primary reference material/calibrators, reference measurement procedures and secondary matrix-based reference materials) had been successfully implemented. With this in mind, an international collaborative study was initiated in 2013 and was conducted in three phases. Phase I involved the assignment of a value in SI units to a primary calibrator, containing a larger amount of C-peptide, using amino acid analyses. Phase II applied this value to the calibration by HPLC of a candidate standard formulated at lower C-peptide content and lyophilized in 2700 glass ampoules. In phase III, the candidate standard was compared to the 1^st IRR (84/510) by current immunoassays to assess its suitability to serve as an International Standard. In this phase, participants were also requested to determine the C-peptide concentration of 16 serum and 16 urine samples in order to assess the impact of the introduction of the candidate preparation on the routine measurement of C-peptide in human samples and to also address commutability considerations. Laboratories were in good agreement in phases I and II, and calibration of the candidate standard by HPLC gave a final estimate of content of 8.64 micrograms per ampoule. The candidate standard also appeared to be sufficiently stable to serve as an international standard, based on the analysis of accelerated thermal degradation samples. The candidate standard was also shown to have appropriate immunological activity in the immunoassay systems included in the study. C-peptide is measured clinically in serum/plasma and urine, and so, using a difference in bias approach (27)in ten of these immunoassay systems to assess the commutability of the candidate standard with serum and urine samples, it was additionally shown that with the exception of two of these assays the candidate standard demonstrated commutability with respect to the serum and urine samples included in the study (30). The First International Standard for C-peptide is now available from NIBSC.

Challenges in implementing the Standardization Process for C-peptide

In 2015 it was clear that three different pure materials were being evaluated for C-peptide. The NMIJ has a high purity material currently available as a CRM and listed in the JCTLM database. The material is lyophilized and can be reconstituted to produce a 100 mg/L solution with an expanded uncertainty of 5 mg/L (k=2). In addition, the NMIJ proposed another ID/MS method as a potential higher order reference measurement procedure for standardization of serum C-peptide; this method is listed on the JCTLM database (29).

The BIPM and NIM China initiated an international comparison in 2014, circulating a C-peptide material to participating NMIs, designed to assess the measurement capabilities of participating NMIs, to measure the mass fraction of C-peptide in C-peptide material expressed in mg/g.

The NIBSC had prepared the 1st WHO International Standard for Human C-peptide NIBSC code: 13/146, and this is now available, replacing the IRR 84/510, stocks of which are exhausted. Each ampoule of the material contains 8.64 μg of C-peptide with an expanded uncertainty of 0.43 μg. Since the material is solely intended to be used as a reference material for immunoassays, it was sent to manufacturers of C-peptide immunoassay methods and shown to be commutable with serum samples for 8 of 10 commercially available immunoassays (30).

The fact that there were several independently developed reference materials for C-peptide in circulation in 2015, with different intended uses, led to confusion at the C-peptide Manufacturer Meeting organized by the NIDDK C-Peptide Standardization Committee and held at the July 2015 AACC Annual Meeting in Atlanta, GA. The intended uses of the different C-peptide reference materials and comparison studies were later clarified; but the co-existence of several different calibration materials, as well as two different calibration hierarchies for C-peptide, within which pure C-peptide was used for direct calibration of IVD kits or only as a calibrator for the reference IDMS measurement procedures, was unsettling to IVD manufacturers at a time when they were initiating re-calibration of their assays to the NIDDK C-Peptide Standardization Committee's reference measurement procedure. This led to the issue being discussed at the JCTLM Members' and Stakeholders' meeting held at the BIPM in December 2015, which led all parties to clarify the status of their activities, and work together to find recommendations for going forward.

Current status of the Reference Measurement System for C-peptide and recommendations for facilitating implementation

Figure 2 illustrates the calibration hierarchy (traceability chain) which the work of Little et al (18) has demonstrated would be necessary to ensure equivalence of C-peptide kit results from different IVD manufacturers. A fully operating reference system for an analyte is expected to have primary reference material, primary calibrators, reference procedures, commutable matrix reference materials, and laboratories operating reference measurement procedures and providing these as measurement services. In order to ensure the quality and accuracy of the measurement values, regular participation in inter-laboratory comparisons is recommended for those laboratories providing reference values, as well as maintenance of appropriate quality systems. The conformity of these systems with written standards can be independently verified by third party peer review or accreditation.

Figure 2.

Traceability scheme for C-peptide, based on a calibration hierarchy that achieves SI traceability, and requires both pure primary reference material and primary calibrator as well as a commutable (matrix based) secondary calibrator.

The reference measurement system for C-peptide as depicted in Figure 2 is in development, and as such the current status of and the proposed next steps for the various components of the system are outlined below.

1. Traceability chain

ISO 17511 outlines various calibration hierarchies (traceability chains) that can be employed to obtain comparable results that agree within their measurement uncertainties. To ensure that values are assigned accurately to IVD kits it is vital that the reference materials used for this calibration step are commutable. Little et al. (17,18) have demonstrated that matrix-based reference materials are necessary within the calibration hierarchy as proposed in Figure 2.

Historically, and in the absence of reference measurement procedures for assigning values of C-peptide concentrations in serum based reference materials, a calibration hierarchy based on pure standards of C-peptide has been employed, as depicted in Figure 3. In this scenario, the Primary Reference Material is to be used directly by manufacturers for assay calibration. The historical use of the WHO IRR for C-peptide (84/510) for direct calibration of IVD kits has meant that for many years a different calibration hierarchy has been in operation. However, for some measurands such as C-peptide, this process has been clearly shown to be ineffective (17). It is now clear that the existence of two different calibration hierarchies will not improve the equivalence amongst C-peptide results from different IVD manufacturers. As a result, upon the establishment of a complete and sustainable reference measurement system for C-peptide to enable manufacturers to calibrate their kits using commutable matrix-based reference materials, it can be recommended that the practice of establishing the traceability of C-peptide results to the WHO International Standard should be discontinued. The status of the International Standard might then change to act as a stable external reference to monitor within-assay performance.

Figure 3.

Historical (and current) traceability scheme for C-peptide, to WHO pure C-peptide material

2. Primary reference material

A primary reference material (pure C-peptide), available from the NMIJ, is listed in the JCTLM database and was produced in compliance with ISO 15194 (also ISO Guides 34 and 35). NMIJ demonstrated its capabilities to value assign a C-peptide pure material in the international comparison coordinated by the BIPM and NIM (CCQM-K115) and as a result, the material is suitable as a primary reference material/calibrator for the IDMS reference measurement procedure as shown in Figure 2. The NMIJ material has not been developed nor evaluated for its suitability for direct calibration of immunoassays.

The WHO International Standard from NIBSC is not suitable for use as a primary reference material for the IDMS reference measurement procedure. This material was produced as a reference material for the calibration of immunoassays, following WHO Guidelines, and the calibration hierarchy model depicted in Figure 3. The material was characterized through an International collaborative study, coordinated by NIBSC, which included the immunoassay manufacturers of C-peptide kits. The results of this study indicated that the standard is commutable for several, but not all, immunoassay methods.

3. Reference measurement procedures

Two IDMS reference measurement procedures are published in the JCTLM Database for the measurement of C-peptide in serum, one from NMIJ and the other from DDL. Both procedures cover similar ranges and report similar achievable relative expanded uncertainties within the reference range for C-peptide of about 10%. Method validation work at DDL demonstrated that their reference measurement procedure operated in two different laboratories could lead to agreement within 5% of reported values, within the measurement uncertainty of the procedures (20). However, the NMIJ and DDL results, although very well correlated (r²=0.986), currently exhibit a bias of ∼20%, which is outside the combined measurement uncertainty of both methods. The two IDMS measurement procedures differ in their source of primary calibrator, extraction procedure, labeled internal standard and mass spectrometric analysis (with or without a derivatization step). The possible causes of bias are currently under investigation by both laboratories.

When the sources of bias between the two IDMS methods are identified, and corrective action is initiated, the information listed in the JCTLM database will be updated accordingly. In the meantime, a note will be added advising users of the discrepancy between these two methods. In addition, the JCTLM procedures for the review of new reference measurement procedures will be reviewed as it pertains to the situation where reference measurement service data from the IFCC External Quality assessment scheme is not available to demonstrate method result equivalence.

4. Commutable matrix certified reference materials

Implementation of this part of the traceability chain is currently foreseen through value assignment of serum samples with the reference measurement procedure(s), as currently no certified reference materials for C-peptide in serum are available or listed in the JCTLM database. The serum samples need to be sufficiently homogeneous and stable to meet their intended use and for them to be considered reference materials. The provision to industry of reference measurements on patient samples, provides an alternative acceptable mechanism to a commutable CRM.

5. Reference measurement services

At least three laboratories have operated reference measurement procedures for C-peptide and could provide these as reference measurement services to the IVD industry. JCTLM listing of a reference measurement service provider requires the listed laboratory to: use a JCTLM listed reference measurement procedures; participate regularly in inter-laboratory comparisons for reference laboratories (e.g. IFCC quality assessment scheme); and be accredited to ISO 17025 and 15195 for the service. Currently no laboratories are listed in the JCTLM database as providing C-peptide reference measurement services. As the reference system for C-peptide is implemented it is expected that to continue to demonstrate the accuracy of the reference measurement system, reference laboratories will participate in inter-laboratory comparisons.

6. External quality assessment for clinical laboratories

Accuracy based external quality assessment schemes for C-peptide will enable the equivalence of results on patient samples to be monitored and the success of the harmonization process to be demonstrated. Assessment scheme providers should be encouraged to adopt accuracy based systems as has been done for HbA1c (31). A pilot serum survey (“wild card challenge”) recently took place in the College of American Pathologists 2016survey (2016-B ING) for C-peptide.

Conclusions

From the above description it is clear that different organizations, laboratories and individuals involved in harmonization efforts are often separated by distance and funding mechanisms. This can cause lack of coordination among the parties involved that can hinder the process of achieving global harmonization. Clearly effective communication and coordination of activities is important for progression through the harmonization process. The recently established International Consortium for Harmonization of Clinical Laboratory Results (ICHCLR) provides a forum for communication to support planning and coordination of harmonization activities among different stakeholders at an early stage (13). The current C-peptide situation is a good example where better communication would have led to cooperation and earlier implementation of a reference system for harmonization of medical laboratory measurement procedures. The JCTLM, in addition to overseeing a listing of Reference Materials, Measurement Procedures and Laboratory Services can provide a forum for interaction among all organizations/laboratories involved with harmonization activities. The most recent JCTLM meeting held in Sèvres France on November 30 to December 1, 2015 enabled discussion of C-peptide harmonization activities with better communication among all interested parties regardless of their countries of origin and funding streams.

Unfortunately, the timeframe for successful implementation of harmonization of clinically important analytes is long. Development of reference materials and measurement procedures is difficult, time consuming and needs to be sufficiently funded if it is to be successful. It is important that the goals for a given analyte be decided at the beginning of a harmonization activity, including the model for the calibration hierarchy to be applied, as well as interaction between all bodies that will eventually contribute to a sustainable reference measurement system for an analyte at an early stage in the development of that system. Better communication will certainly help achieve this coordination. The JCTLM stakeholders meeting was useful in bringing various organizations together once a problem had been identified. The ICHCLR coordinating activities for early collaboration is also a practical way to avoid such problems arising in the future.

A new reference measurement system for C-peptide measurements is proposed, and we have identified some next steps required to successfully implement and sustain that system. In addition, C-peptide harmonization history provides a good case study of the challenges for the harmonization process, and the collaborations and interactions required to make it a success.

Abbreviations

BIPM

Bureau International des Poids et Mesures

CCQM, Consultative Committee for Amount of Substance

Metrology in Chemistry and Biology

CRM

certified reference material

DDL

Diabetes Diagnostic Laboratory

ICHCLR

International Consortium for Harmonization of Clinical Laboratory Results

ID-LC/MS

isotope dilution liquid chromatography mass spectrometry

IDMS

isotope-dilution mass spectrometry

IRB

Institutional Review Board

IRR

International Reference Reagent

ISO

International Organization for Standardization

IVD

in-vitro diagnostics

JCTLM

Joint Committee for Traceability in Laboratory Medicine

NIBSC

National Institute of Biological Standards and Control

NIDDK

National Institute of Diabetes and Digestive and Kidney Diseases

NIM China

National Institute of Metrology in China

NMI

National Metrology Institute

NMIJ

National Metrology Institute of Japan

WHO

World Health Organization