The Use of NESTROFT for Screening Pregnant Women for Detection of β-Thalassemia Carriers

Abstract

The thalassemias and sickle cell disorders are widely distributed in India and cause a significant health burden [1, 2]. Community control programmes are the only way to reduce this burden. Screening for identification of carriers forms an integral component of a prevention programme [1, 2]. The often-debated questions are whom to screen and which would be the most appropriate technology to be used. The individuals targeted for screening in most studies include school or university students, newly-married couples, pregnant women, extended family members of a thalassemia major child, or members of communities where the prevalence of b-thalassemia carriers is higher than the average of 3 %–4 % in the Indian population. Pregnant women would be the most appropriate group as they are the ones at immediate risk but they often come late in the second trimester of pregnancy to the antenatal clinic for their first visit, especially in public hospitals, and it is often difficult to get their husbands for testing [3]. All these target groups have been screened in India by different centers [4–7]. Premarital screening is largely not acceptable due to fear of stigmatization. The technologies used for screening and diagnosis, include the following: Naked eye single tube red cell osmotic fragility test (NESTROFT); red cell indices; discriminant functions; flow cytometric osmotic fragility; and hemoglobin analysis by high-performance liquid chromatography (HPLC), capillary electrophoresis, or cellulose acetate electrophoresis for estimation of Hb A2, Hb F or other hemoglobin variants. A combination of these methods has been used by different investigators and each one has its advantages and limitations [8–13]. NESTROFT has been used as a primary screening test for population screening in many studies after Kattamis et al. first showed that a 0.36 % saline solution was sensitive and effectively detected more than 96 % of b-thalassemia carriers on screening [14]. The ideal approach would be to measure the red cell indices and quantitate Hb A2, Hb F, and any other hemoglobin variant by HPLC or capillary electrophoresis in every individual to ensure that all b-thalassemia heterozygotes as well as carriers of abnormal hemoglobins are identified. However, this is not a cost-effective strategy for massscreening programmes in a large country. Moreover, even with this ideal strategy, around 2 % of b-thalassemia heterozygotes who have normal red cell indices, and/or normal or borderline Hb A2 levels will be missed. NESTROFT has a high sensitivity but lower specificity as shown in several studies [8–13]. Using NESTROFT as a single first-line screening test has some limitations. Although it has a high negative predictive value, few bthalassemia carriers have been missed in different studies. In a quality control evaluation done during the large multicenter study of Indian Council of Medical Research (ICMR) under the Jai Vigyan programme, the main reasons for higher number of false negatives at some centers were the quality of water used, inaccurate dilution of the buffer, and frequent change of technicians. It was also shown that if NESTROFT was combined with measuring red cell indices in the first step itself using mean corpuscular volume (MCV) \80 fL and mean corpuscular hemoglobin (MHC)\27 pg as cut-off values, the b-thalassemia carriers & Roshan B. Colah colahrb@gmail.com