Old tests and new paradigms: How to interpret iron studies and related biomarkers for the diagnosis of iron deficiency in adults.

Clinicians need a good understanding of available tools to diagnose iron deficiency (ID). Interpretation of commonly used laboratory tests can be challenging due to the dynamic nature of iron homeostasis and concurrent inflammation, which influence results. The misinterpretation of iron studies, inconsistencies in ID diagnostic guidelines, and low awareness of non-anaemic ID may lead to missed diagnoses and opportunities for treatment. Serum ferritin (SF) is the most specific routine test for diagnosing ID, but should be interpreted in the correct context. Low SF levels provide a clearcut diagnosis, whilst normal and raised SF levels in the setting of inflammation require a nuanced diagnostic approach. Limited evidence to support diagnostic SF cut-offs and uncertainty surrounding SF reference intervals represent ongoing challenges. This paper aims to provide clarity on the utility and limitations of various laboratory tests for ID and to demonstrate their interpretation with practical examples.