[Frequency of HIV positivity in donors. Follow-up of ambiguous Western blots (letter)]

This work reviews the incidence of indeterminant or false positive results of HIV screening for potential blood donors in Spain who reported no risk factors for HIV transmission and reports the results of follow-up of such cases. During 1987-90 29334 samples were screened. Samples reactive to the ELISA test were retested with the same technique. Results positive on repetition or with absorbencies situated at 10% of the cutoff value were confirmed simultaneously with Western blot and an ELISA test using recombinant antigens of the HIV core and envelope (Envacore). In cases with indeterminant results follow-up and repeat analysis 1-8 months later were advised. Criteria of positivity were those proposed by the World Health organization. 119 reactive samples were those proposed by the World Health Organization. 119 reactive samples were detected in the 1st ELISA screening representing .41% of the samples processed. 108 of these were negative when the ELISA was repeated. The remaining 11 samples demonstrated reactive or indeterminant results. 4 of the 11 samples were from persons with risk factors whose seropositivity was confirmed with Western blot and recombinant ELISA. In the other 7 accounting for .02% of all samples analyzed the results of confirmation tests were indeterminate. All 7 showed reactivity to various proteins without fulfilling the Western blot criteria for positivity. Follow-up was possible for 6 of the 7 donors with indeterminant Western blots. In 5 cases the bands disappeared completely in an average time of 5.2 +or- 1.7 months. Additional reactivity appeared in only 1 case. Recent results of positive tests for HIV antibody screening among Spanish blood donors have ranged from 0 to 2.1% with the national average rate of confirmed positives at .24%. The rate of indeterminate Western blots was similar to that in foreign series from areas of low incidence of AIDS. In cases of indeterminate Western blots a system of reporting the results is needed to assure that the blood bank is fully informed and that reliable evaluation is possible during follow-up. This work suggests that donors with indeterminate results should be followed for at least 6 months.