Spot urine is a suitable matrix for measurement of copeptin

To validate urine as a suitable matrix for copeptin measurements, derive a urinary copeptin/creatinine ratio in an apparently healthy sample of the population, and assess pre-analytical conditions such as collection type and storage temperatures that affect stability and recovery.

Matrix effect was determined by spiking the manufacturer's calibrator F simultaneously into pooled serum and aliquots of spot urine sample donated by a single volunteer. Stability was assessed without preservatives as well as 0.0032×g of thymol or 1 mL of 5 M hydrochloric acid. The urinary copeptin-to-creatinine ratio reference limit was derived from random spot urines collected from 120 apparently healthy volunteers who met the selection criteria.

Our in-house derived urinary copeptin-to-creatinine ratio was<2.5 pmol/mmol creatinine, and there was a statistically significant difference in urinary copeptin concentration between males and females, but this was eliminated when corrected for urine creatinine. 24-h and spot urine with and without preservatives were stable for 7 days at 4-8 °C, 23-25 °C, and -20 °C. Limits of blank, limits of detection, and limit of quantitation were 1.1 pmol/L, and 1.81 pmol/L, respectively.

Urine matrix does not distort the kinetics of the BRAHMS Thermo Fisher Copeptin assay and therefore could be measured with high accuracy. The clinical utility of urinary copeptin is still unknown, however, there is growing interest in this area in patient with autosomal polycystic kidney disease.