False positive PTH results: an easy strategy to test and detect analytical interferences in routine practice

Abstract

Background: As other immunoassays, PTH determination is not free from interferences. Indeed, natural antibodies like heterophile antibodies (HAMA) and rheumatoid factor (RF) can induce falsely elevated results, leading to misdiagnosis and expensive unnecessary explorations. However, in routine practice, these interferences are not always obvious to detect.

Methods: On 2084 PTH samples, we applied a validation strategy in four steps to screen for HAMA and rheumatoid factor interferences.

Results: 36% of our samples presented an elevated PTH. We found a clinically plausible reason for 91% of them. The remaining 63 suspicious samples were treated with HBT and 40% of them were found to be HAMA positive. RF determination was performed on the HAMA-negative samples and RF was positive in 21 of them. They were then treated with RF-Absorbent. Nine of these 21 samples presented RF interference.

Conclusion: Applying this strategy in our routine validation, we managed to avoid spuriously elevated PTH results, which could have caused medical errors as well as unnecessary cost-effective extra-investigations.