Heterophilic antibody interference affecting multiple hormone assays: Is it due to rheumatoid factor?

Assay interference with heterophilic antibodies has been well described in literature. Rheumatoid factor is known to cause similar interference leading to falsely elevated hormone levels when measured by immunometric methods like enzyme-linked immunosorbent assay (ELISA) or multiplex immunoasays (MIA). We report a case of a 60-year-old male patient with a history of rheumatoid arthritis referred to our endocrine clinic for investigation of hypogonadism and was found to have high serum levels of LH, FSH, SHBG, Prolactin, HCG and TSH. We suspected assay interference and further tests were performed. We used Heteroblock tubes and PEG precipitation to eliminate the interference and the hormone levels post treatment were in the normal range. We believe the interference was caused by high serum levels of rheumatoid factor. Although he was treated with thyroxine for 3 years, we believe he may have been treated inappropriately as his Free T4 level was always normal despite high TSH due to assay interference. Our case illustrates the phenomenon of heterophilic antibody interference likely due to high levels of rheumatoid factor. It is essential for clinicians and endocrinologists in particular to be aware of this possibility when making treatment decisions in these groups of patients.

Analysis of 17 α-hydroxyprogesterone in bloodspots by liquid chromatography tandem mass spectrometry.

BACKGROUND: Monitoring of treatment for patients diagnosed with congenital adrenal hyperplasia (CAH) can be performed by measuring the concentration of 17α-hydroxyprogesterone (17OHP) in bloodspots collected on filter papers. A method is described here for measuring 17OHP by liquid chromatography tandem mass spectrometry (LCMSMS). METHODS: 17OHP was extracted by liquid-liquid extraction and analysed by LCMSMS. The method was validated for sensitivity, specificity, linearity, recovery, ion suppression, precision and bias. RESULTS: The standard curve was linear from 0 to 400 nmol/L. Intra-assay %CVs were <10 and inter-assay %CVs were <15 over the range 10-200 nmol/L. Limit of quantitation was 6 nmol/L. No ion suppression was detected. The only interfering compound detected was deoxycorticosterone, an intermediate steroid with the same molecular weight as 17α-hydroxyprogesterone. The method was more accurate and precise than an existing radioimmunoassay. There was poor correlation between the two assays. CONCLUSIONS: We have developed a sensitive and specific assay suitable for quantitation of 17OHP in bloodspots. This method performs better than radioimmunoassay and allows smaller samples to be used.