RESUMO
OBJECTIVE: To modify the method of labelling leukocytes with 99mTc HM-PAO by centrifuging 15 minutes at low gravity (g) instead of sedimentation at a variable time (30-90 minutes) to obtain leukocytic rich plasma (LRP). METHODS: The g number recovering the greatest number of leukocytes was determined. The cellular composition of LRP obtained by centrifugation and sedimentation was analyzed. Lastly, labelling results in two groups of patients (p) were compared: one group of 118 p using the traditional sedimentation method (SM) and another of 124 p using the proposed centrifugation alternative (CM). RESULTS: Centrifugation at 5xg produced the greatest recovery of leukocytes (93.1 5.1%). No significant difference was observed in leukocyte recovery in LRP obtained either by centrifugation or by sedimentation. However, red blood cell contamination was greater in centrifugation (12.8 4.9 x 108) than in sedimentation (7.7 3.5 x 108) (p < 0.0001). The comparison of the SM and the CM gave the following results:The number of leukocytes recovered in both methods was similar (73.9 15.1% vs 76.5 12.7%) with approximately the same platelet contamination (8.0 6.2 vs 8.4 6.5%). The number of red blood cell contaminants per leukocyte was 3.0 1.0 for the MS and 5.1 2.6 for the MC (p < 0.001). Labelling yield (LY) was somewhat higher for the CM (57.8 11.9%) than for the SM (50.8 12.6%) as a result of greater red blood cell contamination and superior radiochemical purity of the 99mTc HM-PAO used in the labelling by CM (90,9 5,9%) with regard to the SM (87.9 9.5%). No difference was observed in the scintigraphic images obtained with either of the methods, given the scarce uptake of the radiopharmaceutical by the red blood cells (3-7%) in comparison with the leukocyte uptake (70-90%). CONCLUSION: The proposed MC considerably reduces the labelling time of leukocytes with 99mTc HM-PAO without affecting the quality of scintigraphic images and represents an important labelling alternative of great interest to the Radiopharmacy Units of Nuclear Medicine Services.
