To Convert or Not to Convert? Official IATDMCT Guideline on Converting Capillary-Blood Microsampling Concentrations to Plasma Concentrations
Boffel et al.
The finding, in our words
Guidance on capillary-to-plasma conversion: method- and analyte-specific clinical validation with paired capillary–venous samples before reporting plasma-equivalent results.
A paraphrase to the Library’s standard, never the abstract. The source is one link away and is always the authority.
In AML and CLL, 91% of VAMS venetoclax results fell within 20% of plasma after individualised haematocrit correction; in home sampling, 18 of 21 patients self-sampled independently and 76% of returned samples were analysable, which shows home microsampling is workable, though the authors ask for multicentre validation.
Volumetric microsampling can enable patient-centred therapeutic drug monitoring with high patient preference and acceptable method validation for many drugs, but conversion from capillary to plasma and agreement with venous sampling varies by analyte and requires careful validation.
Home DBS sampling gave testosterone results that agreed well with venous blood in men on intramuscular testosterone undecanoate, but showed falsely high values in those using topical gel, likely from skin contamination. Patients preferred home collection for its convenience, suggesting DBS is viable for decentralised monitoring of injectable testosterone if patients are taught proper technique.
In matched clinical samples from rheumatoid arthritis, VAMS and DBS showed strong agreement for methotrexate polyglutamates (slopes 0.95-1.07; bias within -4.21% to 0.36%; SRCC ≥ 0.969), with up to 100% of total MTXPG results within ±20% limits; capillary microsampling agreed closely with whole blood but differed from red blood cells, indicating matrix-specific differences that must be accounted for when interpreting against RBC-based reference values.
A UPLC-MS/MS method for linezolid and metabolites in oral fluid and VAMS capillary blood satisfied ICH M10 validation requirements. Linezolid concentrations correlated strongly with venous plasma in both matrices, offering a non‑invasive option for therapeutic drug monitoring, whereas metabolites were systematically underestimated in VAMS and seldom detectable in oral fluid, restricting metabolite measurement.