Screening for Iron Deficiency: Can We Continue To Avoid Ferritin?.

Abstract

Detection of iron deficiency remains poorly understood and costly due to inappropriate screening. Low ferritin is a definitive diagnosis of iron deficiency, but screening with ferritin is not allowed. Therefore surrogates in the blood count have been used to justify obtaining the serum ferritin. The purpose of this research was to analyze the role of Hemoglobin (Hgb), Mean Corpuscular Volume (MCV), and RBC Distribution Width (RDW) as surrogates in screening for iron deficiency. All 2,563 patients with serum ferritin levels gathered over 12 months were reviewed. The relative utility of Hgb, MCV, and RDW in screening for low ferritin levels was shown through multiple Receiver Operator Characteristic (ROC) curves. 264 patients had a ferritin less than 10 ng/ml and 210 between 11 to 20 ng/ml. Results indicate that when viewed independently MCV correlates most closely to low ferritin as seen in Figure 1. RDW and Hgb in both males and females demonstrate a weaker association though remains of value. Table1 lists the values at which the three screening tools were 95% and 100% sensitive for detecting ferritin levels of 10 ng/ml and below. In contrast the data indicate that for ferritin levels from 11 to 20 ng/ml all three screening variables have poor sensitivity and specificity. This is demonstrated clearly in Figure 2. The data suggest that the most severe iron deficiency (ferritin under 10 ng/ml) can be well predicted by abnormalities in the blood count; however less severe iron deficiency (ferritin 10 to 20 ng/ml) cannot be anticipated from the blood count. The blood count does not appear to be a practical alternative to ferritin for screening for iron deficiency. Table 1: Sreening Variable Sensitivities* 100% Sensitivity 95% Sensitivity *values for ferritin less than 11 ng/ml MCV >98.2 >90.0 RDW <12.2 <13.1 Hgb Males >15.0 >13.7 Hgb Females >14.2 >12.6 Figure 1 Figure 1. Figure 2 Figure 2.