Abnormal Kidney Function in Anorexia Nervosa

Abstract

Source: Gurevich E, Steiling S, Landau D. Incidence of impaired kidney function among adolescent patients hospitalized with anorexia nervosa. JAMA Netw Open. 2021;4(11):e2134908. doi:10.1001/jamanetworkopen.2021.34908Investigators from Schneider’s Children’s Medical Center of Israel, Petach Tikva, Israel, and Sackler School of Medicine, Tel Aviv, Israel, conducted a retrospective study to assess kidney function in children and adolescents hospitalized with anorexia nervosa (AN) and identify predictors of impaired kidney function (IKF) in these patients. For the study, discharge diagnoses were used to identify youths, 9-18 years old, hospitalized at Schneider’s Children’s Medical Center of Israel for AN between 2010 and 2019. Only youths with a first-time hospitalization for AN were included in the study. Patients with AN were age- and sex-matched to a random sample of control children with normal serum creatinine (SCr) levels, hospitalized for other reasons during the same period. The medical records of study participants were reviewed and data on demographics, BMI, and SCr abstracted. In patients with AN, data on free triiodothyronine (FT3) level and minimal heart rate (HR) also were collected. Kidney function was assessed in study participants using maximal SCr levels, minimal estimated glomerular filtration rate (eGFR) and SCr/BMI ratio during the hospitalizations. These parameters were compared in AN patients and controls using chi-square or Fisher exact tests. AN patients were classified as having IKF if their minimal eGFR during the hospitalization was <90 mL/min/1.73 m2. Stepwise regression was used to identify predictors of IKF in AN patients.A total of 395 youths with AN and 495 controls were included in the analyses. The mean age of AN patients was 14.6 ± 2.2 years, and 298 (81.6%) were female. The median BMI percentile in those with AN was 12.3, compared to 49 in controls (P <0.001). Parameters of kidney function were significantly different between AN patients and controls including maximal SCr (mean values, 0.68 ± 0.15 mg/dL and 0.54 ± 0.14 mg/dL, respectively; P <0.001), SCr/BMI (mean values, 4% ± 1.2% and 2.8% ± 1.1%, respectively; P <0.001), and minimal eGFR (mean values, 99.8 ± 22.0 mL/min/1.73 m2 and 124 ± 26.5 mL/min/1.73 m2, respectively; P <0.001). Among those with AN, 146 (37%) met criteria for IKF compared to 0 control patients. In the group of AN patients, those with IKF had a significantly lower minimal HR than those without IKF (mean, 44 vs 56 beats per minute; P = 0.001) and lower FT3 levels (mean, 3.5 vs 4.1 pmol/L; P = 0.001); there was no significant difference between groups for mean BMI. Independent predictors of IKF in AN patients included SCr/BMI ratio, minimal HR, and systolic and diastolic blood pressure.The authors conclude that IKF is common in youths hospitalized with AN.Dr Sanchez-Kazi has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.AN has a prevalence rate between 0.1% and 2.2%.1 As previously reported, IKF is a known complication of AN with multifactorial etiologies including chronic dehydration, electrolyte derangements, and abuse of certain medications.2 Chronic hypokalemia has been associated with acute kidney injury (AKI) and chronic kidney disease.2 Other electrolyte abnormalities reported with AN and during refeeding include hypophosphatemia, hypomagnesemia, and hyponatremia. (See AAP Grand Rounds. 2021;45(2):16.)2,3 Kidney biopsy has shown interstitial fibrosis, evidence of ischemic injury, and hypokalemic nephropathy.2The biggest limitation of the current study, and all studies of AN, is the inability to accurately determine eGFR. Using creatinine and correction of eGFR per body surface is likely inaccurate due to low muscle mass. The prevalence of IKF in AN may increase or decline depending on the accuracy of eGFR. Using nuclear GFR may be more precise, although cumbersome, or perhaps measurement of serum cystatin C.4,5 Cystatin C, a low molecular weight protein secreted by all nucleated cells, is independent of muscle mass.4,5 BMI was used to correct for low muscle mass in the current study, although this method has not been verified. It is interesting to note that admission BMI did not correlate with eGFR, but minimal heart rate did. Does this suggest that cardiac abnormalities may contribute to reduction in kidney perfusion in AN?Although the current study was performed in Israel, AN is universal. AKI has been associated with longer hospitalization and increased morbidity not only in AN but also in other non-AN conditions.6In adolescent patients hospitalized with recently diagnosed AN, kidney function often is impaired and needs to be followed closely.The global pandemic of COVID-19 has been associated with a marked increase incidence of eating disorders.7 Social distancing, changes in food access and habits, and social pressure exerted through the internet appear to be contributory. Recent AAP guidelines outline the pediatrician’s role in detection and management of children and adolescents with disordered eating.8