Ferritin outperforms other biomarkers in predicting bone marrow iron stores in patients with hematologic disorders

Although iron-deficiency anemia is common, interpreting iron laboratory test results can be challenging in patients with comorbidities. We aimed to study the accuracy of common iron biomarkers compared with bone marrow iron staining in a large retrospective data set of patients with hematologic disorders. We collected from 6610 patients (median age, 66 years) results of iron staining, with their concurrent ferritin, transferrin saturation, soluble transferrin receptor, transferrin, hemoglobin, and mean red blood cell volume results from Helsinki University Hospital electronic health records. In receiver operating characteristics analysis, ferritin had the highest area under the curve (AUC) with 88% (95% confidence interval [CI], 86-90) for females and 89% (95% CI, 87-91) for males in predicting reduced bone marrow iron. Using a ferritin cutoff of 30 μg/L resulted in high specificity rates of 97% in females and 99% in males. However, sensitivity rates were only 54% and 35%, respectively. Other studied biomarkers had inferior AUCs. Multivariate logistic regression models did not significantly perform better in prediction than ferritin alone. With 50% preprobability for reduced iron stores, a ferritin of 30 μg/L (females) and 51 μg/L (males) had a 95% positive predictive value for reduced iron stores. A 95% negative predictive value was achieved at 1750 μg/L (females) and 4967 μg/L (males). In our large population study, ferritin was the best single biomarker for iron deficiency in secondary care. Adding other blood tests in a multivariate model did not improve performance. However, in these patients with hematologic disorders, even a high ferritin did not rule out iron deficiency with 95% certainty.