Capillary UCH-L1 protein blood measurement is affected by sample hemolysis

Glial fibrillary acidic protein (GFAP) and ubiquitin C-terminal hydrolase L1 (UCH-L1) are internationally validated blood biomarkers for the management of mild traumatic brain injury (mTBI). Capillary blood sampling would facilitate point-of-care testing for dual GFAP/UCH-L1 determination, but it is more sensitive to pre-analytical variables such as hemolysis than venous blood measurements. The aim of this study was to compare capillary and venous assays and assess the impact of hemolysis on them.

Paired venous and capillary samples were collected from healthy volunteers and neurocritical care unit patients. GFAP and UCH-L1 were measured using the i-STAT^® Alinity system. Red blood cell hemolysate spiking experiments were performed on different analytical platforms able to measure GFAP/UCH-L1. A human albumin matrix experiment was also conducted to look for intra-erythrocytic presence of GFAP and UCHL-1.

GFAP showed excellent correlation between capillary and venous samples (r=0.99; 95 % CI 0.98-1.0; p<0.001) with no potential clinically relevant impact on diagnostic thresholds. By contrast, UCH-L1 showed poor correlation (r=0.28; 95 % CI 0-0.57; p=0.058) and wide limits of agreement. Hemolysis caused marked overestimation of UCH-L1 using different analytical platforms, whereas GFAP remained stable. Spiking experiments confirmed that UCH-L1 overestimation was related to its presence in red blood cells.

Capillary UCH-L1 is highly sensitive to hemolysis, limiting the reliability of its assay in capillary samples. By contrast, capillary GFAP assay displays robust analytical performance for mTBI management.