Renal injury in pediatric anorexia nervosa: a retrospective study

Abstract

Purpose

Although primarily a mental health disorder, anorexia nervosa (AN) has many physical consequences. Among them, the consequences on kidney function are often underestimated. We evaluated renal function in adolescent AN inpatients and investigated the correlation between the GFR and intrinsic patient characteristics.

Methods

A single-center retrospective study was conducted on 51 patients hospitalized for the restrictive type of AN in 2013. Data were divided into: (1) medical history of AN; (2) growth parameters and vital signs upon admission; and (3) blood tests. The glomerular filtration rate (GFR) was calculated using the Cockroft–Gault, MAYO Clinical Quadratic (MCQ), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), the Modification of Diet in Renal Disease (MDRD), and Schwartz equations.

Results

The calculated percentages of patients with a GFR below 90 mL/min/1.73 m² according to the different equations were as follows: Cockroft–Gault, 45%; MDRD, 28%; CKD-EPI, 14%; MCQ, 12%, and Schwartz, 4%. There was a strong association between the body mass index (BMI) and the GFR according to all equations (p < 0.0001). The lowest heart rate was significantly associated with a reduced GFR according to the Cockroft–Gault equation (p = 0.03). The GFR values did not differ significantly after rehydration.

Conclusion

Clinicians should evaluate AN patients for renal complications, especially when the BMI and heart rate are very low. Dehydration was not solely responsible for renal impairment.

Level of evidence

Level III, single-center retrospective cohort study.

Annex 1

Cockcroft–Gault formula:

$$ {\text{eCcr }} = \, \left( { 1 40 - {\text{ age}}} \right) \, \times {\text{ mass }}\left( {\text{in kg}} \right) \, \times \, \left[ {0. 8 5 {\text{ if female}}} \right] \, /{ 72 } \times {\text{ serum creatinine }}\left( {{\text{in mg}}/{\text{dL}}} \right). $$

Modification of diet in renal disease (MDRD) formula:

For creatinine in mg/dL:

$$ {\text{eGFR }} = { 186 } \times {\text{ serum creatinine}}^{ - 1. 1 5 4} \times {\text{ age}}^{ - 0. 20 3} \times \, \left[ { 1. 2 10{\text{ if black}}} \right] \, \times \, \left[ {0. 7 4 2 {\text{ if female}}} \right]. $$

Chronic kidney disease-epidemiology collaboration (CKD-EPI) formula:

$$ {\text{eGFR }} = { 141 } \times { \hbox{min} }\left( {{\text{SCr}}/{\text{k}}, 1} \right)^{\text{a}} \times { \hbox{max} }\left( {{\text{SCr}}/{\text{k}}, 1} \right)^{ - 1. 20 9} \times \, 0. 9 9 3^{\text{age}} \times \, \left[ { 1.0 1 8 {\text{ if female}}} \right] \, \times \, \left[ { 1. 1 5 9 {\text{ if black}}} \right], $$

where SCr is serum creatinine (mg/dL), k is 0.7 for females and 0.9 for males, a is −0.329 for females and −0.411 for males, min indicates the minimum of SCr/k or 1, and max indicates the maximum of SCr/k or 1.

MAYO clinic quadratic (MCQ) equation:

$$ {\text{eGFR }} = { \exp }\left( { 1. 9 1 1 { } + { 5}. 2 4 9/{\text{serum creatinine }}{-}{ 2}. 1 1 4/{\text{serum creatinine}}^{ 2} {-} \, 0.00 6 8 6 { } \times {\text{ age}}{-}\left[ {0. 20 5 {\text{ if Female}}} \right]} \right), $$

If serum creatinine <0.8 mg/dL, use 0.8 mg/dL for serum creatinine. eGFR estimated glomerular filtration, eCcr estimated creatinine clearance rate

Schwartz equation:

$$ {\text{eGFR }} = {\text{ k }} \times {\text{ height }}/{\text{ serum creatinine}}, $$

where k = 0.55 for children 1–13 years. k = 0.55 for adolescent females 13–18 years. k = 0.7 for adolescent males 13–18 years