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Background
Health professionals rely on the accuracy and validity of laboratory investigations in managing patients. Occasionally the results of laboratory investigations do not correlate with the clinical scenario. Incorrect pathology results may lead to unnecessary further investigation, inappropriate therapeutic interventions, and considerable anxiety for the patient and doctor. Heterophile antibodies are endogenous antibodies in human serum/plasma that may interfere with immunoassays resulting in false elevation, or rarely false depression of measured values.
Objective
To alert health professionals to clinical situations in which heterophile antibodies may result in misleading results and potentially compromise patient care.
Discussion
Heterophile antibodies may interfere with a number of immunoassays commonly used in clinical practice. Awareness of the possibility of interference by heterophile antibodies is important to prevent inappropriate management on the basis of erroneous laboratory results.
Keywords
antibodies, heterophile; sensitivity and specificity; immunoassay
Case 1
A boy aged 10 years was referred to a paediatric endocrinology clinic following abnormal thyroid function tests performed because of fatigue and short stature. Free thyroxine (FT4) was 12 pmol/L (reference interval 10-26) and thyroid stimulating hormone (TSH) was elevated at 17.2 mIU/L (reference interval 0.1-4). Tests for antithyroid peroxidase and anti-thyroglobulin antibodies were negative. The boy was commenced on thyroxine replacement. Despite a progressive increase in his dose of thyroxine to 100 µg per day and a rise in FT4 to 25 pmol/L, TSH remained elevated. His parents were asked about medication adherence at each visit. After 2 years of thyroxine treatment, testing with heterophilic antibody-blocking studies confirmed interference by a heterophile antibody, TSH being normal with treated serum. The patient's thyroxine treatment was ceased and his thyroid function remained normal.
Case 2
A man aged 42 years with no risk factors for ischaemic heart disease presented to his general practitioner with atypical chest pain. An electrocardiogram was normal; however, his serum cardiac troponin I (cTnI) was elevated at 0.22 µg/L (reference interval <0.04). He was admitted to hospital with a diagnosis of non-ST elevation myocardial infarction. Ongoing chest pain led to urgent coronary angiography, which showed normal vessels. Echocardiography revealed normal left ventricular size and function and normal right ventricular systolic pressure. Over the ensuing days the patient's cTnI remained elevated. Testing confirmed...