Genetic diagnosis in recently transfused patients

Analysis of recently transfused patients is usually postponed to avoid spurious results because of contamination with donor's cells. However, little is known about the extent of this influence in routine molecular diagnostic tests. To elucidate this question, we tested a mix of blood samples from 2 α-1-antitrypsin-deficient patients diagnosed as Pi*Z homozygous with 1 normal donor at 1:1, 1:10, 1:20, and 1:30 proportions. Human identification panel and Pi*Z allele detection were used to establish the detection limit of a blood mixture. Mixtures of 1:1 and 1:10 were easily detected with both techniques, whereas for 1:30, it was necessary to change the equipment settings to identify the mixture. Moreover, the heterozygous pattern observed for the mixtures on Pi*Z genotyping was weaker at this level of mixture. We further evaluated the degree of mixture detectable in 20 transfused patients who received 1 blood unit (concentrate of irradiated or nonirradiated red blood cells) using the human identification panel. Two days after the transfusion, the presence of the donor's markers was not detected, suggesting that after this time point the levels of admixture are below 1:30. The methods applied in the present study showed adequate sensitivity to identify alleles of the so-called "smaller population" of cells up to 3%, approximately. The same result was obtained in a "diagnostic situation," in which the blood mixture was submitted to a PCR-RFLP protocol to detect a mutation.