Could the erythrocyte indices or serum ferritin predict the therapeutic response to a trial with oral iron during pregnancy? Results from the Accuracy study for Maternal Anaemia diagnosis (AMA)

BACKGROUND: Treatment of maternal iron-deficiency anaemia can reduce risks of prematurity and low birth weight; hence a reliable diagnosis of maternal iron needs is critical. However, erythrocyte indices and serum ferritin have shown a weak correlation with iron status during pregnancy. This study verified the accuracy of those tests to predict the responsiveness to a therapeutic test with oral iron as reference standard for iron deficiency in pregnant women. METHODS: A prospective diagnostic study phase 3 was conducted in a single prenatal care center in Northeast Brazil. Between August 2011 and October 2012 a consecutive sampling included 187 women in their 2(nd)-3(rd) trimesters of low-risk pregnancy and having anaemia (haemoglobin <11.0 g/dL). Until December 2012, 139 women completed a trial with daily pills of ferrous sulfate (40 mg of iron), during 23 to 125 days. Haemoglobin (Hb), other erythrocyte indices and ferritin (index-tests) were assessed pre-treatment by automated analyzers. Hb was performed also post-treatment to assess the therapeutic response by its post-pretreatment differences. We estimated sensitivity (Se), specificity (Sp), predictive values (PV), likelihood ratios (LR), diagnostic Odds Ratio (OR), area under Receiver Operating Characteristic curve (AUC), accuracy ratio and agreement coefficient of the index-tests against an increase of at least 0.55 Hb Z-score (reference standard test). We calculated the Z-scores according to the reference population from Centers for Disease Control and Prevention. RESULTS: Hb had a mean increase of 0.24 Z-score after 30 iron pills (p 0.013). All index-tests demonstrated PV- above 70 %, PV+ around 40 %, LR around 1.0, and AUC of 0.5 to 0.6. Hb and haematocrit had Se of 50 % (95 % CI 40 to 70); and Sp of 59 % (95 % CI 43 to 74) and 47 % (95 % CI 38 to 57), respectively. Ferritin, Mean Corpuscular Volume, Mean Corpuscular Haemoglobin, Mean Corpuscular Haemoglobin Concentration and Red blood cell Distribution Width had Se below 40 % with Sp above 70 %. CONCLUSIONS: Erythrocyte indices and ferritin could not predict the iron needs of anemic pregnant women. Increases of Hb Z-scores after a short treatment with oral iron may be a reliable therapeutic test. TRIAL REGISTRATION: World Health Organization International Clinical Trials Registry Platform U1111-1123-2605; Brazilian Registry of Clinical Trials RBR-237wbg, registered 28 July 2011 ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12884-016-1005-x) contains supplementary material, which is available to authorized users.