Screening criteria for beta thalassaemia trait in pregnant women.

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Abstract
AIMS--To establish suitable screening criteria for beta thalassaemia trait during pregnancy using an automated blood counter incorporating light scattering technology. METHODS--Pregnant women (n = 857) at a London antenatal clinic were investigated for beta thalassaemia trait if the Technicon H.2 full blood count showed either a mean corpuscular volume (MCV) < 85 fl or a mean corpuscular haemoglobin (MCH) < 27 pg. Results were then analysed to establish which of these variables was more suitable for screening and to determine suitable cut off points for calculating the haemoglobin A2 percentage. RESULTS--The MCH was superior to the MCV for thalassaemia screening as it was a more stable measurement and fewer unnecessary tests were performed. A MCH less than 27 pg is a suitable cut off point for screening. This screening criterion was equally applicable to a Coulter impedance counter. CONCLUSIONS--Pregnant women presenting at an antenatal clinic with a MCH < 27 pg should be investigated further to confirm or exclude a diagnosis of beta thalassaemia trait.