Does Heparin Affect ^99mTc-MAA In Vitro Stability?

Introduction: Pulmonary embolism (PE) can be diagnosed by perfusion lung scintigraphy 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. Methods: The reconstitution of MAA kit was performed according to the manufacturer'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 differences 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 radiochemical 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.