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.