INTRODUCTION

Iron Deficiency Anemia (IDA) and beta-thalassemia trait (β-TT) are the most common causes of hypochromic microcytic anemias (Wharton, 1999; Olivieri, 1999). Several indices, e.g., England and Fraser (1973), Mentzer (1973), Srivastava and Bevington (1973), Shine-Lal (1977) and Green-King (1989) have been proposed during the past 35 years to discriminate between the two (Sirdah et al., 2008). An ideal discrimination index has a high sensitivity and specificity and is easy to calculate.

Recently researchers developed a new index with such properties (Ehsani et al., 2005). However, before any new index can be safely applied in practice, it should be carefully evaluated and compared with the already existing indices. Here the results of study on 284 patients (130 patients with IDA and 154 with β-TT) are briefly reported.

MATERIALS AND METHODS

Pregnant women as well as patients with a known chronic disease, acute or chronic infections, hemoglobinopathies other than β-TT, or concurrent IDA/β-TT were not included. The new index was calculated by MCV-(10xRBC) and its sensitivity and specificity was compared with the following 4 indices: England-Fraser = MCV-RBC-(5xHb)-k, Mentzer = MCV/RBC, Srivastava = MCH/RBC and RBC count. Youden’s index was calculated by sensitivity+ specificity-100 (Lin et al., 1992; Pekkanen and Pearce, 1999). Informed consent was obtained from all patients and the study protocol was approved by the ethics committee of our university.

RESULTS AND DISCUSSION

Table 1 shows hematological findings of patients. The new index correctly identified 263 (92.96%) patients, standing inferior only to Mentzer which correctly diagnosed 269 (94.71%) patients. The best discrimination index according to Youden’s criteria was Mentzer (Youden’s index = 90.1) followed by the new index (Youden’s index = 85.5) (Table 2, 3).

The discrimination between IDA and β-TT is important because MCV will not normalize in β-TT if misdiagnosed as IDA and treated with iron (Olivieri, 1999). Iran, a country located on the thalassemia belt, is one of the areas with a high prevalence of beta-thalassemia (Lee et al., 1999). On the other hand, iron deficiency anemia is a common problem in Iran, affecting up to 30% of the population by recent estimates (Keikhaei et al., 2007; Kadivar et al., 2003; Karimi et al., 2002; Djazayery et al., 2001). Therefore, the confusion between IDA and β-TT is not uncommon in this country. This problem urged us to compare the value of popular discrimination indices and try to develop a new index which is sensitive, specific and easy to calculate. Based on the above results, the new index and the Mentzer index have high Youden’s indices and are able to correctly diagnose 93-95% of cases while both are easy to calculate.

Table 1:	Hematological findings of patients

Table 2:	Results obtained from each discrimination index

Table 4 provides a brief summary of the results of relevant studies to date. Unlike our study, the Mentzer index was not among the two best discrimination indices in the other five reports. Here, sample size of 284 patients and the fairly small difference between the performance of the Mentzer index and that of the new index do not allow us to draw a firm comparative conclusion. However, the new index may be a suitable alternative, if not a replacement, to the Mentzer index because the difference between the performance of these two indices in our series was attributable to the lower sensitivity of the new index in diagnosing IDA, a problem which can be partly resolved by IDA patients’ suggestive history and manifestations in physical examination. Also, the two indices may work together to provide a more accurate discrimination decision. The present study is the third to apply the new index to a large sample of patients and also the first report from Iran. Due to remarkable inconsistencies between the results obtained so far, it is not possible to choose one discrimination index as the most appropriate and the issue awaits future large studies.

Table 3:	Sensitivity, specificity and Youden’s index of five indices to discriminate between IDA and β-TT in 284 patients

Table 4:	Summary of recent relevant studies
RDWI: Red blood cell distribution width index, *:Studies that considered our index