HL-A 27 and the diagnosis of back problems.

Too much of the information required for rigorous assessment of the diagnostic value of a positive HL-A 27 test is not available. Certainly there would seem to be no case for population screening, not least because effective prophylaxis is not possible. At present sacroiliac radiographs have greater value in the clinical situation, and it seems unlikely that the contribution they make to diagnosis will be challenged. The absence of the HL-A 27 antigen may have some value as an exclusion test, but careful prospective studies are required, as well as a more detailed cost-benefit appraisal of this test.