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Year : 2015  |  Volume : 4  |  Issue : 3  |  Page : 151-155

Role of discrimination indices in screening of beta-thalassemia trait in West Bengal, India: An institutional experience on 10,407 subjects

1 Department of Pathology, Bankura Sammilani Medical College and Hospital, Bankura, West Bengal, India
2 Department of Pathology, Murshidabad Medical College and Hospital, Berhampore, Murshidabad, India
3 Department of Pathology, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal, India

Date of Web Publication9-Dec-2015

Correspondence Address:
Kaushik Saha
42/9/2, Sashi Bhusan Neogi Garden Lane, Baranagar, Kolkata - 700 036, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2278-0521.171430

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Background: Beta-thalassemia trait (BTT) is a common genetic disorder of hemoglobin and imposes a significant burden on global healthcare. Screening of this disorder is immensely important epidemiologically as it can reduce the future incidence of thalassemia major in newborns. The present study was carried out to evaluate the role of six discrimination indices to differentiate cases of BTT from others.Materials and Methods: A single-center, cross-sectional study was conducted on consecutive 10,407 participants. In addition to common diagnostic statistics association, concordance and receiver-operating characteristic curves were assessed to judge the role of discrimination indices. Results: Shine and Lal index, Mentzer index, and Srivastava index had revealed better discriminative function compared to England and Fraser index, red cell distribution width index, and Green and King index. Conclusion: Discrimination indices are rapid, reliable, and easy tools to suspect a case of BTT and send the subject for further high-performance liquid chromatography evaluation. But the cut-off value for these indices needs to be revised to achieve the best combination of sensitivity and specificity in this population.

Keywords: Beta-thalassemia trait, discrimination index, hemoglobin A2, high-performance liquid chromatography, screening, West Bengal

How to cite this article:
Mukhopadhyay D, Saha K, Sengupta M, Mitra S, Datta C, Mitra PK. Role of discrimination indices in screening of beta-thalassemia trait in West Bengal, India: An institutional experience on 10,407 subjects. Saudi J Health Sci 2015;4:151-5

How to cite this URL:
Mukhopadhyay D, Saha K, Sengupta M, Mitra S, Datta C, Mitra PK. Role of discrimination indices in screening of beta-thalassemia trait in West Bengal, India: An institutional experience on 10,407 subjects. Saudi J Health Sci [serial online] 2015 [cited 2020 Jun 2];4:151-5. Available from: http://www.saudijhealthsci.org/text.asp?2015/4/3/151/171430

  Introduction Top

Hemoglobinopathies impose a significant burden on global healthcare. Approximately 5–7% of the global population carries a potentially pathological hemoglobin (Hb) gene. It mainly includes the structural Hb variants and different forms of thalassemias.[1] Accurate and timely detection of various Hb variants including beta-thalassemia trait (BTT) can prevent the occurrence of serious disorders such as thalassemia major in newborns.[2] The application of cation-exchange, high-performance liquid chromatography (CE-HPLC) to separate and quantify various normal and abnormal Hb fractions of clinical significance has been proposed for hemoglobinopathy screening.[3],[4] Hb analysis with HPLC and iron study are expensive for public health economy particularly in countries with high prevalence of microcytosis and hypochromia and not available routinely in low resource settings, whereas the automated blood cell counter is widely used in routine practice.[5],[6]

Since the early 1970s, various discrimination indices derived from simple red blood cell (RBC) indices, such as RBC count, mean corpuscular volume (MCV), mean corpuscular Hb (MCH), and red cell distribution width (RDW) have been advocated as a simple and inexpensive tool. To distinguish between BTT and iron deficiency anemia (IDA) especially for the population, or mass screening programs in developing countries where the resources are limited.[7],[8] There is controversy not only on the choice of red cell indices, but also on the cut-off values to be used for distinguishing thalassemic from nonthalassemic microcytosis. The screening reliability of these indices differs from one country to another. Again, the published cut-off values and interpretations are primarily based on the Western population studies. In spite of all these shortcoming, these indices can be used as a simple screening tool without imposing additional cost to the medical system.[6],[9]

We had conducted our previous study [10] to evaluate the spectrum and frequency of various hemoglobinopathies in the state of West Bengal, India, by the CE-HPLC with the assessment of the common demographic factors and hematological parameters. The present study was carried out on the same study population, to determine the role of six discrimination indices to differentiate cases of BTT from normal subjects as well as from cases of other hemoglobinopathies, and to find out the best discrimination index for that purpose. We also endeavored to find the best cut-off value of each discrimination index in our population.

  Materials and Methods Top

The present single-center, cross-sectional study was carried out on consecutive 10,407 subjects, who were screened by CE-HPLC for hemoglobinopathies in the thalassemia control unit of the Department of Pathology of Institute of Post Graduate Medical Education and Research, Kolkata, after obtaining the proper approval from ethical committee of the institution, and informed consent from the patients. Data of all the subjects during the study period of 3 years and 5 months (01.01.2010–31.05.2013) were retrieved from our database that was maintained and organized by the Linux-based Thalamon software (Venus IT Solutions). Although no absolute exclusion criteria were used, sampling was deferred for at least 4 weeks after or just before next transfusion in patients requiring blood transfusions. The hematological parameters and RBC indices were measured with an automated hematology analyzer (KX-21, Sysmex Corporation, Japan). The red cell morphology and platelet counts were crosschecked with well-prepared peripheral blood films. The HPLC evaluation is done in Bio-Rad Variant Hemoglobin Testing System (Hercules, California, USA) using variant beta-thalassemia short program pack. The Bio-Rad Variant is a fully automated CE-HPLC system to separate and determine area percentages for HbA2 and F, and to provide the qualitative determinations of abnormal Hbs. The subjects with an HbA2 level between 4.0% and 9.0% were diagnosed as BTT. All the abnormal HPLC variants were corroborated with RBC morphology and indices, ethnicity, family history, and HPLC study of the parents and/or other siblings.

Six discrimination indices [11],[12],[13],[14],[15],[16] namely Mentzer index (MI), Shine and Lal index (SLI), Srivastava index (SI), England and Fraser index (EFI), red cell distribution width index (RDWI), and Green and King index (GKI) were used to assess and compare the diagnostic statistics of all the indices to correctly diagnose the cases of BTT from other hemoglobinopathies, and subjects with normal Hb analysis irrespective of their iron status. The differential values for each discrimination index were applied as defined in the original published reports.

Statistical analysis

Continuous variables were expressed as mean ± standard deviation (SD). Categorical variables were presented as frequencies and percentages. Diagnostic statistics was assessed by computing sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR). The association was judged by Yates' Chi-square test. Agreement or concordance was assessed by percent agreement and kappa measurement of the agreement. Receiver-operating characteristic (ROC) curve was analyzed to evaluate the accuracy of an index to discriminate BTT from others, to compare the diagnostic performance of six indices, and to find out best cut-off values for each discrimination index. P value of 0.05 or less was considered for the statistical significance. All the analyzes were done using IBM SPSS statistics software, version 19 and MedCalc software, version

  Results Top

A total of 10,407 subjects were screened for BTT and other hemoglobinopathies during 3 years and 5 months, of which 3378 (32.5%) were males and 7029 (67.5%) were females. Out of 10,407 subjects, 8898 (85.5%) were diagnosed as normal, 579 (5.6%) were detected as BTT, and 522 (5.0%) were detected as HbE carrier on HPLC study. Apart from normal, BTT and HbE carrier, 10 additional variants were encountered.[10] The patients with borderline HbA2 levels (3.5–4%) that could not be explained by iron status, family history, HPLC study of parents, and other siblings, RBC morphology and indices as wells as the patients with unknown HPLC peaks, and suspected variants requiring molecular analyzes were included in the inconclusive category. Mean values with SDs of six discrimination indices in normal subjects, BTT cases, and other hemoglobinopathies were clearly displayed in [Table 1]. Considering specificity PLR, NLR, Yates Chi-square value, percent agreement, and Kappa value, SI is the best index followed by MI and SLI [Table 2]. However, sensitivity, Youden's index (YI) ([sensitivity + specificity] − 100) and area under ROC curve (AUC) value were best in SLI [Figure 1]. MI and SI displayed very close values on statistical analysis. On ROC analysis, optimum cut-off values for all the indices were relatively higher than published cut-off value except in SLI [Table 3]. There was a maximum increase in YI with optimum cut-off value in case of SI (from 50.9 to 76.0) followed MI (from 55.1 to 73.0). EFI, RDWI, and GKI revealed more poor accuracy in terms of, AUC value and YI, which remained around 50 even with optimum cut-off value.
Table 1: Evaluation of discrimination indices in normal subjects, cases of BTT, and all other HPLC abnormalities

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Table 2: Diagnostic statistics, association study, and agreement analysis of six discrimination indices in the differentiation of BTT from normal subjects and cases of other hemoglobinopathies

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Figure 1: Receiver-operator characteristic curve representing the diagnostic statistics of six discrimination indices

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Table 3: Analysis of ROC curve to compare different indices

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  Discussion Top

Discrimination indices based on simple hematological parameters are useful tool for separating uncomplicated cases of BTT from IDA, but they are not generally applicable to pregnant women or children and are not useful in patients, who have both iron deficiency and thalassemia trait.[17] We have studied the predictive power of these indices to screen cases of BTT from others without considering the iron status, so that we can use it as very simple and easy screening tool to find out BTT cases, where HPLC is not available as a first screening tool and refer the subjects for HPLC study.

However, none of these indices aimed to discriminate IDA, and BTT have 100% sensitivity and specificity in any study. YI provides an appropriate measure of the validity of a particular technique or question by taking into account both sensitivity and specificity.[18]

Sirdah et al.[7] and Matos et al.[19] found that GKI and RDWI as most reliable indicators in Palestinian and Brazilian population, respectively, whereas Demir et al.[20] observed RBC count and RDWI as the most dependable indices in Turkish people. Vehapoglu et al.[21] discovered MI as the most useful one in Turkish people. Shen et al.[22] found GKI, EFI, and Ricerca index as the reliable formulations in Chinese children. Ntaios et al.[8] discovered GKI, and Okan et al.[23] noticed GKI and SLI as the best index of Greek and Turkish population, respectively, but Rathod et al.[24] observed better discriminative power in SLI, SI, and MI than RDWI or GKI on Indian population similar to our observations, but the diagnostic power can be improved by revising the cut-off values of these indices. Similarly, Sahli et al.[25] found SI and MI as the most reliable indices to discriminate BTT from IDA with new cut-off values. On the contrary Nalbantoglu et al.,[26] Ferrara et al.,[5] and Beyan et al.[18] observed that none of these different formulations were useful to differentiate BTT from IDA.

In countries with a high prevalence of iron deficiency with co-existence of other factors that can influence the MCV, the cut-off values used for various red cell indices for BTT screening should be recalculated by ROC curves since they may be different from those in the West, where iron deficiency is less common.[9] Shen et al.[22] and Miri-Moghaddam and Sargolzaie [27] concluded that the spectrum beta-thalassemia mutations in each population can affect various RBC indices; therefore, it is suggested to determine the cut-off value for every formula in different populations. The inter-population differences in the effectiveness of formulas in discrimination of BTT from IDA could be due to the differences of molecular spectrum of beta-thalassemic disorders in various countries, the degree of anemia in iron deficient subjects, sample size, and the mean age of subjects.[6]

  Conclusion Top

Discrimination indices depending on automated cell counter–based parameters are rapid, reliable, and easy tools to suspect a case of BTT, and send the subject for further HPLC evaluation. SLI, MI, and SI have good discriminative function compared to EFI, RDWI, and GKI. However, the cut-off value for these indices needs to be revised to achieve the best combination of sensitivity and specificity in this population.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3]

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