Effects of different chelates and labeling media on platelet labeling with In-111

Recently, many variations of In-111 platelet labeling have been introduced with no consistent method currently being used. In an effort to determine optimal In-111 labeling conditions. The authors have studied the effects of different chelates and labeling media on In-111 platelet labeling efficiency (LE). Labeling of human platelets in plasma with In-111-oxine, resulted in a mean LE of 27% at 3 min, 37% at 10 min, increasing to 57% by 60 min. The mean LE using the chelates, tropolone (TROP) and mercaptopyridine-N-oxide (MERC) were 82% and 67%, respectively, at 3 min, with both reaching maximum LE of 89% and 81%, respectively, by 10 min. Oxine sulfate was also evaluated and found to be a poor platelet label due to inconsistent labeling and a maximum LE of only 22%. Labeling in plasma was compared to labeling in non-plasma media, such as, saline, modified Tyrodes, TRIS, and HEPES at pH 6.5 and 7.4. Consistently, LE of 90% could be obtained by 3 min for all In-111 chelates using non-plasma media. Similar results were seen when the different chelates and labeling media were evaluated using rabbit platelets. The results suggest that, although, a moderate LE can be achieved using In-111-oxine in plasma, ifmore » incubated for one hour, the use of non-plasma labeling media, or TROP or MERC as the In-111 chelate, can result in high LE within short incubation times. The authors are currently evaluating the viability of rabbit platelets labeled under those conditions which yielded high LE using kinetic studies to ascertain which of these methods maintains the viability of the In-111 labeled platelets to the greatest degree.« less