A clinical audit of changes in urine pH during the nutritional rehabilitation of adolescent and young adult patients hospitalised with a restrictive eating disorder

Background: Alkaline urine pH has previously been reported in patients with restrictive eating disorders (EDs) over 30 years ago, however its prevalence is not routinely reported. This study carries out a preliminary investigation of the change in urine pH in malnourished adolescent and young adult patients hospitalised with restrictive EDs during an initial two weeks of higher energy nutritional rehabilitation. Methods: A retrospective review was carried out of the medical charts of malnourished adolescent and young adult patients (aged 14–21) hospitalised with restrictive EDs for ≥ 14 days during a 2-year period (January 2018–December 2019) and provided with assertive nutritional rehabilitation. Linear mixed effects models were used to estimate weekly within patient change in urine pH and identify possible associations with degree of malnutrition, medical instability, and purging status. Results: Seventy-nine patients (75 female, 4 male) with mean age 17.3 ± 1.4 years were included. On admission, patients were commenced on mean 2179 ± 476 kcal/day. No incidence was recorded of clinical refeeding syndrome during nutritional rehabilitation. The average decrease in urine pH ≥ 7 from baseline to 1 week of medical refeeding was statistically significant (56.6% vs. 29.9%, p = 0.001). Urine pH decreased from a mean of 7.0 ± 0.9 at baseline to a mean of 6.6 ± 0.7 after one week of refeeding, and further decreased to a mean of 6.5 ± 0.7 by the end of two weeks. Compared with purging patients, for non-purging patients there was a stronger association between medical instability at admission, low percentage median body mass index, and urine pH ≥ 7. Conclusion: The findings of this study suggest a change in urine pH from ≥ 7 to < 7 can be observed after one week of assertive nutritional rehabilitation in adolescent and young adults hospitalised with restrictive EDs. Further research is required to investigate potential mechanisms underlying elevated urine pH observed in patients with restrictive EDs, and the change that is observed during nutritional rehabilitation.