Blood Micro-sampling: An alternative blood collection method for radioiodine therapy dosimetry.

PURPOSE: Collecting venous blood samples from patients post administration of high therapeutic activities results in radiation exposure to staff collecting the blood. This study investigated the use of finger-tip capillary-blood collection as an alternative to the venous-blood collection method recommended by the European Association of Nuclear Medicine (EANM) dosimetry protocol for quantifying 131I concentration in the critical organ after therapeutic dose of 131I.

METHODS

The study included differentiated thyroid cancer patients referred to a thyroid cancer centre at St James's Hospital, Ireland, for therapeutic and diagnostic oral administration of 131I. The 15 patients recruited for this study provided 30 venous and capillary paired-blood samples. The activity concentration of the blood samples was compared between the type of blood (venous vs capillary) and the geometry/volume of the blood (1.0 ml versus 0.03 ml). Other variables were also investigated including administered activities, dose to staff performing the sampling, duration of sampling and time since administration.

RESULTS

Blood samples were taken at 2.0-91.9 h post administration using 0.2 ± 0.0 GBq (n = 2) or 4.0 ± 0.1 GBq (n = 28) 131I activities. There was no significant difference found between different blood sampling types (-1.0 ± 4.3 %, p = 0.223), different blood volumes (-3.2 ± 10.0 %, p = 0.070), or between their combination. No significant correlation was found between the percentage differences and investigated parameters.

CONCLUSION

A high degree of accuracy was achieved with blood radioactivity quantified using capillary blood collection using the finger-prick method. Further validation of the method would be required prior to implementation, to investigate patient specific factors which may affect accuracy.