Undetectable Troponin in a Patient with Ischemic ECG Changes
A 45-year-old woman with relapsing multiple sclerosis presents to the emergency department with three hours of substernal chest pain and diaphoresis. ECG shows 2 mm ST depression in leads V4–V6. She takes biotin 300 mg daily, self-directed, for 'nerve health,' and has done so for a year. High-sensitivity troponin T is <3 ng/L on two serial draws three hours apart, and creatine kinase is normal. The same day's panel shows TSH 0.02 mIU/L (reference 0.4–4.0) and free T4 3.1 ng/dL (reference 0.8–1.8), but she reports no palpitations, weight loss or tremor and has a resting heart rate of 68. The laboratory's troponin, TSH and free T4 assays all use streptavidin-biotin chemistry on the same analyzer. The emergency physician asks whether to activate the catheterization laboratory.
1. What single explanation links these results, and how does assay architecture account for the direction of each bias?
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High-dose biotin is the unifying cause, and the direction of each error is predicted by the assay format.
Sandwich immunoassays use a biotinylated capture antibody and a signal antibody. Excess free biotin saturates the streptavidin solid phase so the capture antibody cannot bind, the signal falls, and the result is falsely low. Troponin T and TSH are sandwich assays - both are falsely low here, which is why a patient with ischemic ECG changes has an undetectable troponin and a suppressed TSH.
Competitive immunoassays use a labelled analyte that competes with the patient's analyte for a limited number of antibody sites. Free biotin again occupies the streptavidin sites, reducing the bound label; the instrument reads less label as more patient analyte, so the result is falsely high. Free T4 is a competitive assay and is falsely high.
The combination - undetectable troponin despite ST depression, suppressed TSH with elevated free T4 in a clinically euthyroid woman - is the classic fingerprint of biotin interference.
2. What should the laboratory and the clinician do now?
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Neither result should be acted on. The laboratory should repeat troponin on an assay that does not use streptavidin-biotin chemistry - a different platform, a point-of-care method without biotin, or a sample pre-treated to strip biotin. Simple dilution is not a reliable fix: it reduces the analyte and the interferent together, so a normal result after dilution proves nothing.
For thyroid testing, the correct action is to stop biotin for at least 72 hours and repeat; there is no urgency because she is clinically euthyroid.
Clinically, an undetectable troponin must not be used to rule out acute coronary syndrome in a patient with symptoms and 2 mm ST depression. Cardiology should be involved and serial troponins obtained on a different assay. Catheterization laboratory activation is a clinical decision driven by the ECG and symptoms, not by a thyroid panel. The key communication is a direct call from the laboratory to the emergency physician before management is finalized.
3. What corrective and preventive actions should the laboratory take?
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Immediate: document the event, notify the laboratory director, and issue an interpretive comment on the affected results. Identify every analyte on the menu that uses streptavidin-biotin chemistry and classify each as sandwich or competitive so the expected direction of bias is known in advance.
Systems: add a supplement question with a hard stop at order entry for biotin, particularly high-dose formulations; place a chart flag; attach an automatic comment to troponin and thyroid results when biotin appears on the medication list; and consider moving troponin to a non-biotin platform if one is available, since troponin cannot wait 72 hours.
Education: circulate the regulatory safety communication on biotin interference to emergency, cardiology and endocrine staff. Audit: review how many patients in the past year had biotin on their medication list and immunoassay results reported, and check whether any were acted on incorrectly. Follow-up should be tracked to closure with an assigned owner and date.