Electronic urine output (UO) measurements are significantly more accurate and reliable than manual measurements

Electronic urine output measurements

A paper recently published in Nature Scientific Reports describes a prospective study conducted with the Clarity RMS at the University of Pittsburgh Medical Center (UPMC).

The study

Hourly urine output (UO) was measured in 44 cardiothoracic surgery intensive care unit (ICU) patients in the first 24 hours post-op.

Three different methods were compared: Hourly weighing of the urine collection bag via a digital scale, hourly UO recordings obtained by the nursing staff, and hourly electronic urine output measurements recorded by the Clarity RMS system.

The results

Accuracy: The mean measurement bias between the Clarity RMS electronic urine output measurements and the scale was significantly lower than the mean bias between the nursing staff recordings and the scale (>17 ml/hr).

For a 70 kg patient, the criteria for AKI by UO is 35 ml/hr, thus a bias of 17 ml approaches 50% of the threshold value, indicating that the accuracy of manual UO monitoring may be insufficient to detect AKI in some patients.

Missed measurements: Compared to only 8.6% missed measurements with the Clarity RMS, 39% of manual hourly recordings were missed by the nursing staff. In addition, these were reported an average of 47 minutes late.  

Furthermore, 6 cases of oliguria (< 0.5 ml/kg/hr) for at least one hour were missed by the nursing staff but detected by the Clarity RMS, including one patient who met UO criteria for AKI.

Risk of infection: The authors comment on the added benefit of real-time contact-less electronic monitoring providing additional protection from contact with patient body fluids and reducing the risk of infection.


Minor J, Smith A, Deutsch F, Kellum JA. Automated versus manual urine output monitoring in the intensive care unit. Sci Rep 11, 17429 (2021). https://doi.org/10.1038/s41598-021-97026-8

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