The main findings of the current study were the low sensitivity (43.8%) and moderate specificity (73.7%) of the RDW in the diagnosis of IDA among pregnant women in Sudan. Previously, hemoglobin was the most commonly used hematological parameter and screening test for IDA [22
]. However, hemoglobin has its limitation in detecting IDA because sufficient time must elapse for iron to have an effect [23
], and hemoglobin may take up to 2 months to show low levels [24
]. A recent study showed that other hematological parameters, which can be estimated via a hemoanalyzer, such as MCV, MCH and MCHC, have poor performance in detecting IDA during pregnancy [16
]. It is possible that these red cell indices (MCV, MCH and MCHC) are mean values, which cannot express the small variation of red cell size that occurs in early iron deficiency [25
]. Changes in the peripheral blood film (e.g., erythrocyte hypochromia and microcytosis) are less prominent during pregnancy than during the non-pregnant condition, even in moderate iron deficiency [26
]. Therefore, there is a need for a screening test that is cheap and has a high reliability and accuracy for identifying iron deficiency.
A recent observation among non-pregnant women of child-bearing age showed that RDW (≥16.1%) had a sensitivity of 59.3% and specificity of 71% [27
]. Another study among pregnant women in the first half of pregnancy (<20 weeks gestation) showed that an RDW ≥15 had a sensitivity and specificity of 46.8% and 95.7%, respectively [28
]. A high sensitivity (82.3%) and specificity (97.4%) for RDW was reported recently among pregnant women [16
]. Different rates of RDW have been reported. For example, Aulakh et al. [29
] found that the sensitivity of RDW was 81.0% and the specificity was 53.4%, and vanZeben et al. [30
] found that the sensitivity of RDW was 94% and the specificity was 59%.
Some points need to be taken into consideration when comparing different studies. First, some reports used a ferritin level of 10 μg/l as a cut-off point for diagnosis of iron deficiency [31
]. Second, there was a difference in the gestational age between our study and previous studies [16
It should be noted that because of the high prevalence of IDA in pregnancy, it is customary in many settings to consider/treat empirically pregnant anemic patients with iron supplements. Therefore, most of the studies, including the current study, were focused and designed to have maximum specificity for diagnosing IDA rather than achieving the most sensitivity.
This study has some limitations. Hemoglobin electrophoresis, serum vitamin B12, and folate tests were not performed. Such tests are important for excluding hemoglobinopathies, early macrocytosis due to folic acid, or vitamin B12 deficiency where RDW may increase. Anemia of chronic disorders also could not be excluded by an appropriate investigation in cases where serum ferritin levels might have been misinterpreted. The other parameters of iron status or profile such as serum iron level, total iron binding capacity and transferrin saturation were not investigated. Screening for submicroscopic malaria (as it is one of the commonest causes of anaemia) was not performed.