Estimation of the uncertainty of values assigned to calibration materials prepared in-house: An example for hydroxychloroquine calibrators in blood-hemolysate-based matrix

BACKGROUND: Hydroxychloroquine is an antimalarial drug that has been prescribed for the treatment of patients with COVID-19 infection. To assist in clinician decision-making, several clinical laboratories have developed and validated measurement procedures in-house based on HPLC or HPLC-MS/MS to measure the mass concentration of hydroxychloroquine in different biological fluids. In these cases, laboratories produce their calibration materials but rarely estimate the measurement uncertainty of their assigned values. Thus, we aimed to show how this uncertainty can be calculated, using the preparation of hydroxychloroquine calibrators in blood-hemolysate-based matrix as an example. METHODS: A bottom-up approach was used to estimate the uncertainty related to the values assigned to end-user calibration materials prepared in-house. First, a specification of the measurand and a measurement equation were proposed. Then, different sources of uncertainty related to the preparation of hydroxychloroquine calibration materials were identified and quantified. Afterwards, the combined uncertainty was calculated using the law for the propagation of uncertainty resulting in the final expanded uncertainty. RESULTS: In this study, the most significant source of uncertainty was that associated with the hydroxychloroquine’s reference material mass obtained via balance, while the smallest contribution was from the uncertainty associated with the hydroxychloroquine reference material purity. CONCLUSIONS: A simple procedure to estimate the measurement uncertainty of values assigned to calibration materials is presented here, which would be easy to implement in clinical laboratories. Also, it could be put into practice for other pharmacological quantities measured by in-house HPLC or HPLC-MS/MS procedures commonly used in clinical laboratories.