Reliability of the current newborn screening action value for beta thalassaemia disease detection in England: A prospective study

Objective: Beta thalassaemias are a group of hereditary red cell disorders resulting in a reduced or absent production of the main adult haemoglobin, adult haemoglobin. In England, the NHS Sickle Cell & Thalassaemia Screening Programme recommends reporting newborn beta thalassaemia disease as an incidental finding when detected whilst screening for sickle cell disease. The current action value to initiate further investigations is 1.5% adult haemoglobin, using high-performance liquid chromatography or capillary electrophoresis. We examined the reliability of this action value. Methods: A 44-month country-wide prospective study using data from 13 newborn screening laboratories in England. Results: There were 81 cases reported with an adult haemoglobin of 1.5% or less at first-line screen, of which nine were lost to follow-up. The six false-positive results were all of 32 weeks’ gestation or less. Of the 66 true-positives, 36 had confirmatory molecular results (11 of these cases also have results from tandem mass spectrometry), 19 had clinical confirmation and 11 had the results of both parents available which were consistent with the screening result. There was one false-negative, a confirmed beta thalassaemia major case with an adult haemoglobin of 1.7%, above the action value at first-line screen but known to be at risk from parental results and therefore referred into clinical care by the laboratory. Conclusions: This study demonstrates a positive predictive value of 91.7%, with a specificity of 99.9% and a sensitivity of 98.5%. These results confirm the reliability of the current action value.