To the Editor
Correct interpretation of laboratory test results is paramount in avoiding misdiagnosis and incorrect management that could potentially be harmful to patients. In this letter, we illustrate an unusual presentation of hepatitis B viral markers with an uncommon explanation.
A Caucasian female in her mid to late 50s with primary hyperparathyroidism was referred for the evaluation of a positive hepatitis B surface antigen (HBsAg) result while undergoing examination for surgical removal of a parathyroid adenoma. She had no gastrointestinal complaints or risk factors for viral hepatitis except for possible sexual contact. Physical examination did not reveal stigmata of chronic liver disease. Liver function tests were within normal limits, including an alanine transaminase of 13, and evaluation for viral hepatitis A, C, and D were unremarkable. Serum calcium and parathyroid hormone (PTH) levels were elevated at 2.77 mmol/L (2.15-2.55) and 163.9 pg/mL (15.0-65.0), respectively. Results from three pre-operative hepatitis B virus (HBV) panels obtained over five weeks are shown in Table 1.
Table 1. Results of our patient's hepatitis B testing.
| Test* | HBsAg** | S/CO*** Ratio | Neutralization Test Result | HBcAb | HBeAg | HBeAb | HBsAb | HBV DNA |
|---|---|---|---|---|---|---|---|---|
| 1 | positive | 3.13 (average 3.07) | non-confirmable | negative | not detected | |||
| 2 | positive | 9.24 | no confirmation necessary | |||||
| 3 | positive | 9.70 | no confirmation necessary | |||||
Abbreviations – HBcAb, hepatitis B core antibody; HBeAb, hepatitis B e antibody; HBeAg, hepatitis B e antigen; HBsAb, hepatitis B surface antibody; HBsAg, hepatitis B surface antigen; HBV DNA, hepatitis B virus deoxyribonucleic acid; S/CO, signal-to-cut-off
Tests 1-3 were performed over a 5-week period prior to the patient's surgery.
The VITROS® Immunodiagnostic Products HBsAg assay was performed on a VITROS® ECiQ Immunodiagnostic System.
Per manufacturer (Ortho Clinical Diagnostics®), S/CO ratio was reported if the HBsAg result was positive. An initial S/CO >5.0 indicated a positive result that did not require confirmation. An equivocal 0.9 ≥ S/CO ratio ≤ 5.0 underwent repeat testing (average value reported) with a subsequent neutralization test.
A false positive HBsAg was initially suspected given the patient's uncharacteristic test results. The presence of heterophilc antibodies was confirmed when a fourth pre-operative HBsAg (not shown in Table 1) resulted negative after the addition of a heterophilic blocking reagent. Although elevated PTH has been shown to interfere with immunoassays1, this was not the causative factor, as our patient's HBsAg remained positive despite normalization of serum calcium and PTH four weeks after surgery. On repeat testing seven weeks after surgery, the HBsAg became negative, thereby supporting the notion that the responsible heterophilic antibodies circulated in the patient's serum for up to 7 weeks after adenoma removal. Therefore, it is highly suspected that the patient's false positive HBsAg was due to heterophilic interference from a paraneoplastic syndrome related to her parathyroid adenoma. To the best of our knowledge, this is the first reported case in the literature.
The diagnosis and management of HBV infection relies heavily on biomarkers and laboratory values2. Surface antigen testing is part of the initial screening to detect acute and chronic hepatitis B infection2. Active or resolved infection would each have resulted in the presence of other detectable serologic HBV markers2. Transient HBsAg has been observed in patients for up to 2 weeks after HBV vaccination3, but our patient had not been vaccinated and had repeatedly positive HBsAg results for more than a month. The fluctuating HBsAg titers seen in this case may have resulted from changes in secretions from the parathyroid adenoma which also caused serum calcium and parathyroid hormone levels to fluctuate. Heterophilic antibodies have been known to cause both falsely positive (e.g. human immunodeficiency virus)4 and falsely elevated (e.g. prostate-specific antigen)5 immunoassay results. These naturally-occurring human antibodies bind to a wide variety of chemical structures, including the animal antibodies often used in immunochemistry assays1, and can be neutralized by a reagent composed of specific inactivating binders5. In an era of increased reliance on laboratory values in disease management and despite advances in modern assays methods, clinicians should be cognizant of the rare but important challenges posed by heterophilic antibodies, particularly when test results are discordant with other clinical findings.
Acknowledgments
Financial Support: This document was supported by the Intramural Research Program of the National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.
Abbreviations
- DNA
deoxyribonucleic acid
- HBcAb
hepatitis B core antibody
- HBeAb
hepatitis B e antibody
- HBeAg
hepatitis B e antigen
- HBsAb
hepatitis B surface antibody
- HBsAg
hepatitis B surface antigen
- HBV
hepatitis B virus
- PTH
parathyroid hormone
Footnotes
Disclosures: None.
Author Contributions: DMT was involved in acquisition of data and drafting of the manuscript. DMT, CK, and TH interpreted the data. CK and TH provided critical revision of the manuscript for important intellectual content.
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