Accurate urine sodium measurements at home using point of care testing in patients with short bowel syndrome

Background and aims

Measurement of the urine sodium concentration (USC) is a simple procedure that in many patients adequately indicates their hydration status. This is of particular importance in patients suffering from short bowel syndrome (SBS), who may very rapidly dehydrate and are at risk for permanently compromising their kidney function. A point of care testing (POCT) that allows reliable measurement of USC would enable these patients to effectively evaluate their sodium- and water balance in the at home setting, thereby avoiding hospital visits and delayed test results. In this study, a POCT device to assess USC was first analytically validated after which it was applied for the at home evaluation of the hydration status in patients with SBS.

Methods

First, we validated the imprecision, bias and limit of quantification of USC as measured with the Fisic Medimate POCT device in comparison to an automated routine chemistry system. Next, the device was used for monitoring USC at home in 21 patients with SBS, including an evaluation of user friendliness System Usability Scale (SUS) and accuracy for detecting low sodium levels as compared to the routine chemistry system.

Results

The imprecision of the POCT device at low USC was 6.1 %. In samples at the clinical decision threshold to identify patients at the verge of dehydration of 20 mmol/l as measured by routine chemistry USC, the POCT device demonstrated a mean estimation of USC of 20.6 mmol/l (95 % CI 18.8–22.4). Dehydration was detected with a sensitivity of 95 % when the medical decision limit for urinary sodium on the POCT device was set at a safe concentration of 30 mmol/l. Using the device was straightforward and easy to learn for patients with an overall System Usability Scale (SUS) score of 86.

Conclusion

USC measurements using this POCT device can be safely integrated into daily practice for early detection of dehydration in patients with SBS. Clear patient instructions to ensure accurate drop dispensing and a higher clinical decision threshold of USC of 30 mmol/l will allow a high sensitivity for detecting dehydration in patients with short bowel syndrome.