Fig. 1.

Decision tree for labelling clinical validation quality of the bioanalytical assays. The study label is based on the sum scores of all quality criteria (scores of: 4 = blue, 3 = green, 2 = yellow, and 0–1 = red), except the black label, which refers to the conclusion of the authors of the included studies (“author’s opinion”) that the assay is not applicable for MAM and/or TDM regardless of other criteria. Each study label therefore represents the degree of method validity and clinical applicability. The “author’s opinion” refers to the original authors of the included studies. MAM medication adherence monitoring, NS not sure (maybe, possibly) or no statements made, TDM therapeutic drug monitoring