Pre-operative Waterlow score and outcomes after kidney transplantation.

BACKGROUND

Waterlow scoring was introduced in the 1980s as a nursing tool to risk stratify for development of decubitus ulcers (pressure sores) and is commonly used in UK hospitals. Recent interest has focussed on its value as a pre-op surrogate marker for adverse surgical outcomes, but utility after kidney transplantation has never been explored.

METHODS

In this single-centre observational study, data was extracted from hospital informatics systems for all kidney allograft recipients transplanted between 1 January 2007 and 30 June 2020. Waterlow scores were categorised as per national standards; 0-9 (low risk), 10-14 (at risk), 15-19 (high risk) and ≥ 20 (very high risk). Multiple imputation was used to replace missing data with substituted values. Primary outcomes of interest were post-operative length of stay, emergency re-admission within 90-days and mortality analysed by linear, logistic or Cox regression models respectively.

RESULTS

Data was available for 2,041 kidney transplant patients, with baseline demographics significantly different across Waterlow categories. As a continuous variable, the median Waterlow score across the study cohort was 10 (interquartile range 8-13). As a categorical variable, Waterlow scores pre-operatively were classified as low risk (n = 557), at risk (n = 543), high risk (n = 120), very high risk (n = 27) and a large proportion of missing data (n = 794). Median length of stay in days varied significantly with pre-op Waterlow category scores, progressively getting longer with increasing severity of Waterlow category. However, no difference was observed in risk for emergency readmission within 90-days of surgery with severity of Waterlow category. Patients with 'very high risk' Waterlow scores had increased risk for mortality at 41.9% versus high risk (23.7%), at risk (17.4%) and low risk (13.4%). In adjusted analyses, 'very high risk' Waterlow group (as a categorical variable) or Waterlow score (as a continuous variable) had an independent association with increase length of stay after transplant surgery only. No association was observed between any Waterlow risk group/score with emergency 90-day readmission rates or post-transplant mortality after adjustment.

CONCLUSIONS

Pre-operative Waterlow scoring is a poor surrogate marker to identify kidney transplant patients at risk of emergency readmission or death and should not be utilised outside its intended use.