Academic journal article Bulletin of the World Health Organization

A Simplified Screening Strategy for Thalassaemia and Haemoglobin E in Rural Communities in South-East Asia

Academic journal article Bulletin of the World Health Organization

A Simplified Screening Strategy for Thalassaemia and Haemoglobin E in Rural Communities in South-East Asia

Article excerpt

Introduction

Thalassaemia and haemoglobinopathy are the most common inherited disorders among humans, and they represent a major public health problem in many areas of the world, including south-east Asia (1). The most important disorders are [alpha]-thalassaemia and [beta]-thalassaemia. Among the structural haemoglobin (Hb) variants, Hb E ([[alpha].sub.2][[beta].sup.26glu-lys.sub.2]) is the most common, especially in the north-eastern part of Thailand, and in Cambodia and Laos (2, 3). A high incidence of Hb E (more than 50%) has been reported in many groups with a Mon-Khmer linguistic affiliation (4).

In these areas, the prime targets of prevention and control of severe thalassaemia are homozygous [[alpha].sup.0]-thalassaemia (Hb Bart's hydrops fetalis syndrome), homozygous [beta]-thalassaemia and [beta]-thalassaemia--Hb E disease (5, 6). The aim of screening for thalassaemia and Hb disorders is to offer carrier testing to every member of the population, ideally before they have children, in order to identify carrier couples and inform them of the risk and their options. The people targeted by screening are therefore carriers of [[alpha].sup.0]-thalassaemia, [beta]-thalassaemia and Hb E.

As a general guideline, primary screening for all forms of thalassaemia involves using an electronic blood-cell counter to provide accurate erythrocyte indices. Individuals who have hypo-chromic microcytosis with mean corpuscular volume (MCV) below 80 fl of mean corpuscular Hb (MCH) below 27 pg should bc investigated further using Hb electrophoresis or high-performance liquid chromatography (HPLC) (7, 8). This, however, can be problematic in rural areas in south-east Asia where the expense usually precludes the possibility of electronic blood-cell counting. We evaluated a cheaper alternative screening method using a combination of a modified one-tube osmotic fragility (OF) test (9, 10) and a modified dichlorophenolindophenol (DCIP) precipitation test (11). This method could be used in any primary health care setting where a programme of prevention and control is needed.

Methods

Participants and haematological analysis

One ml of peripheral blood anticoagulated with ethylenediaminetetraacetic acid (EDTA) was obtained from 301 healthy unrelated Thai-Khmer individuals (age range, 8-30 years) living in the provinces of Surin and Burirum in north-eastern Thailand. Informed consent was obtained, and each participant received a written report of the results of the screening tests.

After collection, all samples were immediately screened for thalassaemia using the modified one-tube OF test. They were screened for Hb E using the modified DCIP precipitation test. The modified DCIP test kit, which uses a clear reagent, was developed in out laboratory (12, 13). AU blood samples were put on ice and transferred within six hours to the Faculty of Associated Medical Sciences, Khon Kaen University, for determination of erythrocyte indices using the Coulter-STKS automated blood-cell counter (Coulter Electronics, Hialeah, FL, USA).

Screening test

The OF test was performed as described previously (9, 10) but with slight modification. Instead of using a 0.36% buffered saline solution, we used a 0.34% saline solution in the same buffer. This modification can significantly reduce the number of false-positive samples without changing the sensitivity to [[alpha].sup.0]-thalassaemia and [beta]-thalassaemia (13). In the reagent kit, the 0.34% buffered saline is prepared for each screening in a 13 mm x 75 mm capped plastic tube. A sample of 20 [micro]l whole blood is mixed with 2 ml of the saline solution in the test tube and left at room temperature for 15 minutes before being interpreted. For the DCIP precipitation test, 20 [micro]l whole blood is added to 2 ml of a modified DCIP reagent, and the tube is incubated at 37[degrees]C for 15 minutes before 20 [micro]l of stopping agent is added. …

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