LQCL2602 - CMLE - Clinical Chemistry : A Case of Diagnostic Confusion-LQCL2602

LQCL2602 - Educational Activity

Pdf Summary

A clinical chemistry case highlights how high-dose biotin (vitamin B7) supplements can cause misleading immunoassay results and diagnostic confusion. A 38-year-old woman presented with mild fatigue but had laboratory findings suggestive of hyperthyroidism (very low TSH and high free T4) plus “undetectable” cobalamin. Her vital signs and physical exam did not match thyrotoxicosis, and repeat testing on a new sample produced similar abnormal results, prompting thyroid imaging and an endocrinology referral.<br /><br />Further history revealed she was taking 10 mg/day of biotin for hair and nail health—far above the recommended 30–100 µg/day. The endocrinologist contacted the laboratory, and the team determined the assays used (streptavidin–biotin-based chemiluminescent microparticle immunoassays) were susceptible to biotin interference. Mechanistically, excess biotin in patient samples disrupts streptavidin–biotin binding steps: in sandwich assays (e.g., many TSH methods) it can displace biotinylated capture components and produce falsely low results, while in competitive assays (e.g., some free T4 methods) it can yield falsely high values. Together, these artifacts can mimic thyrotoxicosis and drive unnecessary imaging, referrals, or treatment.<br /><br />The lab recommended stopping biotin for at least 72 hours (the clinician held it for one week) and repeating tests; results normalized (TSH, free T4, and B12 all within reference ranges), confirming interference rather than true disease. The laboratory documented the event, updated pre-analytical collection guidance to capture supplement use, and educated medical staff. The document emphasizes mitigation strategies such as serial dilutions (looking for nonlinearity), testing with alternative methods or reference labs, recollection after washout, and using EHR prompts to flag biotin use.

Keywords

biotin interference

vitamin B7 supplements

immunoassay false results

streptavidin-biotin assay

chemiluminescent microparticle immunoassay

TSH falsely low

free T4 falsely high

thyrotoxicosis mimic

high-dose biotin 10 mg

biotin washout 72 hours