Indian Journal of Pathology and Microbiology

: 2016  |  Volume : 59  |  Issue : 2  |  Page : 262--263

Discriminant indices for thalassemia screening: Need for a higher sensitivity

Ranjeet Singh Mashon, Naveen Kakkar 
 Department of Pathology, Christian Medical College, Ludhiana, Punjab, India

Correspondence Address:
Ranjeet Singh Mashon
Department of Pathology, Christian Medical College, Ludhiana - 141 008, Punjab

How to cite this article:
Mashon RS, Kakkar N. Discriminant indices for thalassemia screening: Need for a higher sensitivity.Indian J Pathol Microbiol 2016;59:262-263

How to cite this URL:
Mashon RS, Kakkar N. Discriminant indices for thalassemia screening: Need for a higher sensitivity. Indian J Pathol Microbiol [serial online] 2016 [cited 2021 Jun 16 ];59:262-263
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We read with interest the article by Sehgal et al. in which the authors have addressed the issue of low-cost screening difficulties of beta thalassemia trait (BTT) and iron deficiency anemia (IDA), both of which present with microcytic anemia. The authors have proposed, evaluated, and validated a new cost effective and rapid red cell count based index (Sehgal Index) for screening of beta thalassemia in a tertiary care hospital setup. The authors have also emphasized upon the need of screening test to have a high sensitivity, without compromising on the specificity.[1]

In their study, the authors have compared three groups: Pure BTT, BTT with coexisting IDA and the third group (all non-BTT cases irrespective of their iron levels). However, no pure IDA cases have been recruited. Thus, the specificity of the evaluated indices does not necessarily imply the specificity of the indices to discriminate between BTT and IDA.

Rathod et al., in a similar study, recruited 200 cases in three groups: Pure BTT, BTT with coexisting IDA and non-BTT cases.[2] Their study showed mean corpuscular volume (MCV) alone to be one of the best discriminating factors in the differentiation of BTT (with and without IDA) and non-BTT. The MCV cutoff of 76 fl showed a high sensitivity and specificity in the classic BTT group (93.7%; 96.6%) and BTT with IDA group (94.8%; 93.33%). In the present study, additional evaluation of MCV as a discriminating factor would have been interesting. Given that the cases recruited in the present study had a high MCV cutoff of 120 fl (without iron studies), the sensitivity and specificity observed in the study are low for the suggested indices (Mentzer's and Sehgal) to be used as a screening tool, especially in a tertiary care hospital.[1]

The sensitivity and specificity of Mentzer's Index as reported by Madan et al. was comparable to that reported by Sehgal et al.[1],[3] However, in the study by Madan et al., the discriminating groups were BTT and confirmed IDA (both usually present with microcytic anemia) with sensitivity - 89.2% and specificity - 74.8% whereas in the study by Sehgal et al., BTT cases were compared to non-BTT (not restricted to IDA) (sensitivity - 88.3%; specificity -76.3%). Considering the recruiting criteria, a higher specificity was expected in the present study since a large number of patients with non-microcytic (normal or raised) indices have been included.

Sehgal et al. have noted the relatively high G and K Index area under curve (AUC) (99%) reported by Urrechaga et al., but the wide variation in the findings of the two studies was not discussed. Further, the notable difference in the discriminating ability of Mentzer's Index between the two studies was overlooked. Mentzer's Index had AUC (95.8%), sensitivity (94.3%) and specificity (84%) as reported by Urrechaga et al. whereas the same in the study by Sehgal et al. was 80%, 83%, and 76%, respectively.[1],[4]

The authors have not mentioned the proportion of antenatal women in their study. This is significant as the discriminant indices fare poorly in pregnant women.[5] The hematological parameters (hemoglobin/red blood cell count/MCV/red cell distribution width) in the patient population with BTT and those with associated IDA would have been interesting to note. The authors mention that cases suspected for hemoglobinopathies were included. It is not clear as to how this population was screened. It is also mentioned that the cases with hemoglobinopathies were excluded from analysis, but the analysis has been shown in 1022 cases which includes these cases. For specificity and sensitivity, the number of cases for each cutoff index has not been provided.

In conclusion, Sehgal et al. have proposed an index which has a sensitivity of 88% and specificity ranging from 57.8% to 86.9% for BTT screening. For a heterozygote (carrier) state of a genetic disease such as beta thalassemia, the homozygous counterpart of which can cause a life-threatening disease with a lifelong transfusion requirement, we feel that any screening tool proposed should keep a target for a higher sensitivity. In a tertiary setting where this index is proposed to be used, the sensitivity of the screening tool should not be compromised.

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Conflicts of interest

There are no conflicts of interest.


1Sehgal K, Mansukhani P, Dadu T, Irani M, Khodaiji S. Sehgal index: A new index and its comparison with other complete blood count-based indices for screening of beta thalassemia traitin a tertiary care hospital. Indian J Pathol Microbiol 2015;58:310-5.
2Rathod DA, Kaur A, Patel V, Patel K, Kabrawala R, Patel V, et al. Usefulness of cell counter-based parameters and formulas in detection of beta-thalassemia trait in areas of high prevalence. Am J Clin Pathol 2007;128:585-9.
3Madan N, Sikka M, Sharma S, Rusia U, Kela K. Red cell indices and discriminant functions in the detection of beta-thalassaemia trait in a population with high prevalence of iron deficiency anaemia. Indian J Pathol Microbiol 1999;42:55-61.
4Urrechaga E, Borque L, Escanero JF. The role of automated measurement of RBC subpopulations in differential diagnosis of microcytic anemia and ß-thalassemia screening. Am J Clin Pathol 2011;135:374-9.
5Yeo GS, Tan KH, Liu TC. The role of discriminant functions in screening for beta-thalassaemia traits during pregnancy. Singapore Med J 1995;36:615-8.