The serum ferritin level is the most sensitive and specific initial laboratory test for iron- deficiency anemia (IDA) in patients with inflammation. Serum ferritin levels <45 ng/dL confirm IDA, and levels of ≥100 ng/dL essentially rule it out (strength of recommendation [SOR]: B, systematic review of prospective validating cohort studies with heterogeneity). For patients with intermediate serum ferritin levels (45-99 ng/dL), the soluble transferrin receptor (sTfR) level and the sTfR-ferritin index (ratio of sTfR to log ferritin) are highly sensitive and specific. An sTfR-ferritin index of ≥1.5 is diagnostic of IDA, even in the presence of acute or chronic inflammation (SOR: B, systematic review of prospective validating cohort studies that lacked standardized reference values)
