Venous-capillary blood agreement for routine chemistry analytes: effects of collection site and sample matrix

Capillary blood sampling enables minimally invasive testing and decentralized workflows, but interchangeability with venous specimens may depend on collection site, device, and matrix.

We conducted a single-center, paired clinical study of 480 adults yielding 960 capillary specimens (fingertip lancet and upper-arm microneedle device) together with matched venous samples. We evaluated three capillary matrices (serum, heparin plasma, K₂EDTA plasma). Routine analytes (n=18) spanning lipid, kidney, thyroid, and cardiac panels were measured on a single integrated platform (Cobas^® Pro c503/e801/ISE). HIL (hemolysis, icterus, lipemia) indices governed sample acceptance. Method comparability followed Clinical and Laboratory Standards Institute (CLSI) EP09 and EP35 and clinical relevance was assessed using the desirable total allowable error (TEa) specifications from the EFLM Biological Variation Database.

Capillary and venous results were clinically comparable for 16/18 analytes when specified HIL cutoffs were applied, although potassium and chloride showed limited interchangeability. Agreement was strong for most measurands across matrices and sites; small, collection site-dependent offsets were observed for selected analytes (e.g., albumin [method-dependent], creatinine [method-dependent], triglycerides, C-reactive protein (CRP), N-terminal pro B-type natriuretic peptide (NT-proBNP), HDL-cholesterol) yet remained within TEa. Fingertip collections yielded larger volumes and fewer collection failures than TAP Micro Select but showed higher hemolysis.

Under routine acceptance criteria, capillary testing demonstrates acceptable performance for most clinical chemistry analytes across matrices. For potassium and chloride, device- and collection-site-related effects warrant further evaluation. This protocol integrates collection-site and matrix assessment and constitutes one of the largest evaluations of venous-capillary interchangeability and supports adoption of decentralized testing workflows.