Table 1. The scheme for multicenter reference interval studies.

The total testing process The process phases	Responsibility	Action
Preanalytical phase	Central laboratory#, All participating laboratories*	1. Organization of the study Establishing the inclusion and exclusion criteria Informing each laboratory of the sample size Deciding the essential items in the questionnaire and distributing to all participating laboratories Communicating with the participating laboratories and informing about the procedures (e.g. blood collection and preparation of the serum samples) to standardize the pre-analytical phase in each laboratory # 2. Using the same protocol in each laboratory (e.g. selection and preparation of the volunteers, blood collection and sample preparation) #,* 3. Transportation of the samples to central laboratory * 4. Storing of the remaining samples for cross-check study in each laboratory*
Analytical phase	Central laboratory#, All participating laboratories*	1. Using a reference measurement system, certificated reference materials/value assigned sera, standardization of the assays # 2. Quality control of the assays #,* 3. Analyzing all the samples # 4. Analyzing the cross-check samples *
Postanalytical phase	Central laboratory#, All participating laboratories*	1. Reporting of the test results to each laboratory # 2. Data analysis and derivation of the RIs (common RIs, if it’s possible) # 3. Reporting of cross-check results and the RIs for each of the local laboratory # 4. Using the calculated RIs #,*

RIs - Reference intervals.