Blood volumes study: development and application of a challenged aseptic simulation test

Introduction
In nuclear medicine, the blood volumes measurement is based on radioisotopic cell labelling. Indeed, a preparation of autologous red cells labelled with technetium 99m (^99mTc-RC) is carried out to determine the globular volume. It comes with a preparation of serum albumin radiolabelled with iodine 125 (¹²⁵I-SA) which allows the determination of the plasma volume.
The preparation of ^99mTc-RC is a complex, multi-stage aseptic process, carried out in an open system. There is therefore a high-risk level of microbiological contamination.
The objective of this work is to ensure the asepsis of our process through an challenged aseptic simulation test (AST).

Method
2 ASTs were developed: one to simulate the preparation of 3 doses of ¹²⁵I-SA (29 steps, 4 samples) and one to simulate the preparation of 99mTc-RC and the syringe filling of ¹²⁵I-SA (129 steps, 18 samples).
The culture medium used was tryptic soy broth (TSB). Fluorescein was added to simulate radiopharmaceutical drugs and be able to trace any radioactive contamination. The septa of all the vials used were intentionally contaminated with a solution of Staphylococcus epidermidis.
Based on the chapter 2.6.1 of the European Pharmacopoeia, the AST method was tested with 5 microbiological strains by performing a fertility test on TSB. The fluorescein’s fertility was previously validated.
Then the asepsis of the preparation processes for ^99mTc-RC and ¹²⁵I-SA was tested. Each AST was carried out 6 times: 3 times respecting the aseptic technique rules (“clean” ASTs) and 3 times not respecting them (“dirty” ASTs).

Results
The AST method was validated since microbiological growth was observed within the time allowed during fertility and applicability tests.
The asepsis of the ^99mTc-RC and ¹²⁵I-SA preparation processes was also validated because the samples from the 3 “clean” ASTs remained clear while a turbidity was observed for those from the 3 “dirty” ASTs.

Discussion-conclusion
Conventional ASTs are not suitable for hospital pharmacies since, due to the small number of units produced, their sensitivity is too low. Therefore, they need to be optimised, for example by contaminating the septa of the vials with a bacterial solution. This allowed us to significantly improve the sensitivity of our ASTs. In addition, the use of fluorescein enabled us to observe possible radioactive contaminations.
The asepsis of the preparation processes involved in the study of blood volumes was therefore verified.
The developed ASTs will allow us to carry out the qualification of our operators.