Does Heparin Affect 99mTc-MAA In Vitro Stability?

Abstract

Introduction: Pulmonary embolism (PE) can be diagnosed by perfusion lung scintigra-phy using human albumin macroaggregates labelled 99mTc (99mTc-MAA). When PE is suspected, subcutaneous Low Molecular Weight Heparin (LMWH) should be administered even before the results of the PE diagnostic flowchart. In our study, we aimed to evaluate a possible interaction (in vitro interference) between 99mTc-MAA and LMWH. Materials and Methods: The reconstitution of MAA kit was performed according to the manufac-turer's instruction. After labelling, we carried out the following preparations: a standard dose of 99mTc-MAA alone, as control; 99mTc-MAA and enoxaparin at different ratios. According to the manufacturer's instruction, the radiochemical purity was performed and evaluated immediately (T0), after 15 and 30 minutes after incubation (T15 and T30). Results: We compared the radiochemical purity of 99mTc-MAA with: (i) radiochemical purity of 99mTc-MAA and enoxaparin (11 ratio), (ii) radiochemical purity of 99mTc-MAA and enoxaparin (0.5 ratio), and (iii) radiochemical purity of 99mTc-MAA and enoxaparin (ratio 2). No significant differ-ences were found between all the measured parameters at each time point for each ratio. We also tested the stability of 99mTc-MAA in physiological conditions (at 37°C in PBS): the initial radio-chemical purity of 99mTc-MAA was 99.78%. The values of 99mTc-MAA radiochemical purity were high in all conditions of possible interaction with LMWH, with values ranging from 98.00% at T0 to 95% at T30. Conclusion: We found no statistically significant change in the in vitro stability of 99mTc-MAA in the presence of enoxaparin, excluding a possible direct interference. Future studies will be needed to check the 99mTc-MAA stability under physiological conditions.