One time genotypic or phenotypic analysis of thiopurine methyltransferase (TPMT) and nudix hydrolase (NUDT15) may be considered medically necessary in patients beginning therapy with azathioprine, mercaptopurine, or thioguanine OR in individuals on thiopurine therapy with abnormal complete blood count results that do not respond to dose reduction.
Genotypic and/or phenotypic analysis of the TPMT and NUDT15 genes is considered investigational in all other situations.
Analysis of the metabolite markers of azathioprine and mercaptopurine, including 6-methyl-mercaptopurine ribonucleotides and 6-thioguanine nucleotides, is considered investigational.
