Early diagnosis of severe combined immunodeficiency syndrome.

Infants with severe combined immunodeficiency syndrome (SCIDS) have a greatly improved prognosis if diagnosed and treated before they develop overwhelming infection. Clinical and laboratory data on 45 patients with SCIDS were retrospectively reviewed to assess the value of absolute lymphocyte counts in making an early diagnosis. Ninety infants matched for age, sex, and presenting symptoms were used as controls. Thirteen (29%) infants with SCIDS were diagnosed at birth as previous siblings had been affected; 32 (71%) were diagnosed after the development of symptoms. Eighteen (56%) of these remained undiagnosed until after 6 months of age. The first symptoms occurred at a median of 5 weeks (range 1 day to 8 months) and the first admission to hospital was at 4 months (range 1 week to 16 months). Symptoms included respiratory infection (91%), vomiting and diarrhoea (81%), failure to thrive (88%), candidiasis (50%), and skin lesions (28%). The mean lymphocyte count was 1.71 x 10(9)/l compared with 7.2 x 10(9)/l in controls. Excluding one child with Omenn's syndrome (lymphocyte count 23.3 x 10(9)/l, all symptomatic infants with SCIDS had lymphocyte counts less than 2.8 x 10(9)/l at presentation. The median delay between the first abnormal lymphocyte count and diagnosis was seven weeks (range one day to 13 months). Twenty eight (88%) of 32 infants would have been diagnosed before 6 months of age if investigated after the first low lymphocyte count. These data indicate that low lymphocyte counts are predictive of SCIDS. Paediatricians are urged to pay attention to the absolute lymphocyte counts in all infants in whom a full blood count is performed. Those with lymphocyte counts persistently less than 2.8 x 10(9)l should be investigated for SCIDS.