LQPB260X - CMLE - Clinical Chemistry : A Case of Diagnostic Confusion-Clinical Chemistry : A Case of Diagnostic Confusion

Clinical Chemistry : A Case of Diagnostic Confusion

Pdf Summary

This ASCP LabQ Phlebotomy case study highlights how high-dose biotin (vitamin B7), commonly taken in over-the-counter “hair, skin, and nails” supplements, can interfere with laboratory immunoassays and create misleading results. A 38-year-old woman presented with mild fatigue and had routine testing that showed a markedly low TSH, elevated free T4, and undetectable cobalamin (vitamin B12), suggesting hyperthyroidism and B12 deficiency. However, her vital signs and physical exam were not consistent with thyrotoxicosis, and repeat testing produced similar abnormal values. Thyroid imaging was also unrevealing.<br /><br />A more detailed history by endocrinology uncovered that the patient was taking 10 mg/day of biotin—far above the recommended daily intake of 30–100 µg. The document explains that many immunoassays rely on the extremely strong streptavidin–biotin binding system for analyte capture and detection. Excess biotin circulating in patient samples can disrupt this system: it can cause falsely high results in some competitive immunoassays (e.g., free T4) and falsely low results in some sandwich immunoassays (e.g., TSH) by displacing biotinylated assay components from streptavidin-coated surfaces. Together, these erroneous results can mimic thyrotoxicosis and prompt unnecessary referrals, imaging, or treatment.<br /><br />The laboratory and clinicians concluded the abnormalities were likely due to biotin interference in chemiluminescent microparticle immunoassays. The patient stopped biotin for one week, after which TSH, free T4, and B12 normalized, confirming interference. Recommended mitigation strategies include holding biotin for at least 72 hours before retesting, performing serial dilutions to assess nonlinearity, using alternative methods less susceptible to biotin, and/or sending samples to reference labs. The case emphasizes communication between providers and laboratory staff, pre-analytical screening for supplement use, staff education, and potential EHR prompts to reduce diagnostic error.

Keywords

biotin interference

vitamin B7 supplements

streptavidin-biotin immunoassay

TSH falsely low

free T4 falsely high

sandwich vs competitive immunoassays

chemiluminescent microparticle immunoassay

thyrotoxicosis mimic

laboratory diagnostic error

biotin washout 72 hours