Comparative study of suggested reference values and observed distributions in daily routine of a medical laboratory

Introduction The Consensus Guidelines of the TDM-AGNP working group contains a comprehensive list of therapeutic reference ranges, often derived from clinical trials with strict predefined inclusion criteria [1]. The goal of this study is to analyze whether these ranges are reflected in routine patient care using samples from a medical laboratory.

Methods The drugs analyzed include aripiprazole (N= 9,640), olanzapine (N=6,074), venlafaxine (N=6,291) plus desmethylvenlafaxine (N=3,512), and lithium (N=9,640). Anonymized data was extracted from the routine archive, plotted as frequency histograms and data distributions were fitted. The observed distribution was compared with the published reference ranges.

Results Aripiprazole, olanzapine, and venlafaxine blood levels followed a lognormal distribution, whereas lithium blood levels were best described by a loglogistic curve. Frequency of samples in relation to current reference ranges varied widely across the four substances: 19.7-25.8% of values were lying below and 1.8-14.6% of values above the current ranges.

Conclusion Interquartile ranges of all substances were located within the lower left of the current reference ranges. Of note, the lower quartiles (25th) for lithium, aripiprazole, and olanzapine corresponded well with the lower values of the published reference ranges.

Conflict of interest

None

Publication History

Article published online:
08 November 2022