Stored plasma samples (paired - acidified and non-acidified) from the specimens collection ('Tumorbiobank') of the Charité Comprehensive Cancer Center will be analysed by HPLC/MS.~A total of 136 samples from patients post Voraxaze across 3 levels of MTX concentrations:~30 without additive, 10 with 0.9% NaCl, 30 with HCl (stored at -80C) 9 without additive, 9 with HCl (stored at +4C and analysed after 3-5 days) 9 without additive, 9 with HCl (stored at -20C and analysed after 3-5 days) 30 with HCl (stored at +4C versus ambient temperature)
Acidification (i.e., addition of hydrochloric acid) of plasma samples from patients who have received Glucarpidase post high-dose MTX treatment is regarded as a necessary preanalytic step to avoid further in vitro enzymatic cleavage of MTX. However, it is unclear whether this acidification step is essential. A comparative study, which evaluates concentrations of MTX and its metabolites in paired (acidified versus non-acidified) plasma samples, has not yet been performed. Processing plasma samples without acidification would facilitate quantification of MTX, including plasma samples from patients treated at centers without adequate laboratory facilities.