The laboratory diagnosis of haemoglobinopathies
The laboratory diagnosis of haemoglobinopathies, including the thalassaemias, is of growing importance, particularly because of an increasing requirement for antenatal diagnosis of significant disorders of globin chain synthesis. This guideline discusses the laboratory tests which are most useful in the diagnosis of haemoglobinopathies and describes their role in specific clinical circumstances. Of the newer technical methods, high-performance liquid chromatography (HPLC) is of considerable importance whereas isoelectric focusing (IEF) and immunoassay for variant haemoglobins have a more minor role. Specific recommendations have been formulated for testing in relation to genetic counselling and for neonatal diagnosis. Methods used in specialized laboratories for fetal diagnosis have been tabulated. Genetic counselling requires: (i) identification of haemoglobins S, C, D-Punjab, O-Arab, E, Lepore and H, and (ii) the detection of carriers of alpha(0) and beta thalassaemia. It is recommended that subjects of all ethnic groups be screened for beta-thalassaemia trait, all except Northern European Caucasians for variant haemoglobins, and selected ethnic groups for alpha(0)-thalassaemia trait. Testing for beta-thalassaemia trait should be carried out when the mean cellular haemoglobin (MCH) is < 27 pg and testing for alpha(0)-thalassaemia trait should be considered when the MCH is < 25 pg. Appropriate methods include HPLC or haemoglobin electrophoresis for identification of variant haemoglobins and HPLC or microcolumn chromatography for quantification of haemoglobin A2.