Should platelets be radiolabelled in plasma medium?

Because of the low labelling efficiency of platelets with In-111 oxine in plasma containing media, most investigators have labelled platelets in plasma-free media. However, labelling of platelets with In-111 oxine in plasma-free media may result in either: irreversible damage leading to rapid clearance from the circulation and permanent hepatic sequestration; or reversible damage with transient hepatic sequestration without affecting the in vivo survival. Since human platelets can be labelled with In-111 oxine in plasma in sufficient efficiency for routine clinical use, they should be labelled in plasma whenever possible. The use of newer In-111 chelates, tropolone and mercaptopyridine-N-oxide, which label platelets with high efficiency in plasma as well as in plasma-free media, may offer another alternative.