Variation in Thyroid Function Tests in Acute Scrub Typhus Infection.

INTRODUCTION

Immunoassays used to measure thyroid function tests (TFTs) are prone to interference due to several factors that could potentially affect clinical decisions. With increased awareness and frequency of testing TFT, even 1% prevalence of assay interferences would possibly increase the occurrence of deranged TFT significantly. In this study, we report six cases of thyroid hormone assay interference in acute scrub typhus infection.

METHODS

A prospective observational study was conducted in patients admitted with acute scrub typhus infection. TFT was done for some indication that showed discordance with clinical suspicion. Initial assay was performed by electrochemiluminescence immunoassay (ECLIA) using a Roche Cobas e411 analyzer, which was verified by Chemiluminescent Microparticle Immuno Assay (CMIA) with an ARCHITECT i1000SR analyzer.

RESULTS

Initial TFT done by ECLIA showed elevated FT4 and FT3(FT4>> FT3) with a normal or low-normal TSH in all cases. Samples were re-analyzed in the CMIA platform within 24 hours, which showed normal TFT, raising the suspicion of assay interference. TFT performed by ECLIA 6 weeks after recovery was normal in all patients.

CONCLUSION

Assay interference with TFT should always be considered when there is a discrepancy between clinical suspicion and biochemical values. It is prudent to confirm abnormal values on another platform to avoid misdiagnosis and unwarranted therapeutic decisions.