Laying the foundation for enhancing safety of desmopressin in older people: Validation of capillary blood sodium levels

Purpose: We aim to make desmopressin a safe treatment option for (older) patients at risk for hyponatremia, by introducing a new way of sodium monitoring. The goal is to reduce the risk of hyponatremia, enhance patient safety and ultimately introduce self-monitoring of sodium levels. The first step in the aforementioned is to validate capillary sodium. Materials and Methods: 100 randomly selected patients admitted to the urology department received a single finger prick to collect capillary blood (250 µl) in a lithium-heparin tube. Each patient acted as its own control for the capillary and venous blood sample. Venous and capillary plasma sodium were analyzed by indirect ion-selective electrode measurement. The primary outcome was the agreement between capillary and venous sodium measurements, measured by the intra-class correlation coefficient (ICC). Results: One hundred paired blood samples were obtained of which four were excluded. There was no significant statistical difference observed between venous and capillary sodium (−0.23 mmol/L, p = 0.374). The ICC for single measures between capillary and venous sodium was 0.82 (95% confidence interval 0.75–0.88). Inter-method differences analyzed by a Bland–Altman plot and a Passing–Bablock regression did not reveal a statistically significant difference between both groups. Conclusions: We demonstrated that venous and capillary sodium levels are interchangeable, taken into account the inter- and intravariability between analyses. We provided the first step towards a simple and safe solution for frequent sodium monitoring through a minimal invasive capillary blood collection. The results are of direct clinical relevance to safely use desmopressin in (older) patients at risk.