Granulocyte radiolabeling using Leukokit® with introduction of a density gradient medium as ancillary material.

BACKGROUND

Radiolabeled white blood cells (WBCs) prepared in radiopharmacies are used to detect infectious or inflammatory sites with scintigraphy. Radiolabeling can be performed by using a disposable closed device, Leukokit®. Nevertheless, owing to the high radiosensitivity of lymphocytes, the question of eliminating lymphocytes before granulocyte radiolabeling is still a controversial step. The aim of this study was to assess a new modified Leukokit® with a protocol that allows granulocyte radiolabeling only.

METHODS

Seventy patients (male/female: 40/30, mean age: 61 years) with suspected infectious diseases underwent labeled leukocyte scintigraphy by radiolabeling with a density gradient medium in addition to Leukokit®. Compliance and quality of radiolabeling were checked according to the following criteria: visual inspection, labeling efficiency, cell viability (Trypan blue exclusion test), cell subset recovery test, lymphocyte elimination rate (granulocyte/WBC rate) and sterility test using media fills.

RESULTS

Visual inspection showed that all cell preparations were free of residual cell clumps or fibrin clots. Mean labeling efficiency was 70.4±9.4% compliant with EANM Guidelines for leukocyte labeling. The mean cell viability was 97.7±1.4% (>96%). The mean number of leucocytes injected was 116x106 ±62x106 (>50x106). The mean erythrocyte/WBC ratio was 2.1 ±0.9 (<3) and the removed lymphocyte rate was 97.4±1.6% (>90%). Finally, the three sterility tests were negative and therefore successful.

CONCLUSIONS

Purification of granulocytes with Leukokit® can safely, easily and effectively be performed using a density gradient medium. Moreover, clarification regarding the status of density gradient medium could provide support for its clinical use even if further studies are needed. Since all technical obstacles have been removed, the precautionary principle should apply and lead users to eliminate lymphocytes that are highly radiosensitive cells and whose in vivo fate is uncertain.