Kidney Failure and Eating Disorders
By Elissa Rosen, MD, CEDS-S
Kidneys are able to perform remarkably complex functions in order to maintain homeostasis in our bodies. One of the major functions of the kidneys is to filter our blood in order to balance electrolytes, maintain optimal fluid levels, and excrete toxins. While this process is exquisitely fine-tuned and complex, the kidneys also must be treated well in order to function well. Many things can disrupt kidney function including medications, dehydration, and imaging contrast materials to name a few. In certain types of eating disorders, kidney failure is more common. For purposes of this blog we are going to talk about acute kidney failure (now better known as acute kidney injury), generally defined as developing over 48 hours or less, and chronic kidney disease, which develops over greater than 48 hours and many times over a period of months to years.
Before we delve into this, let’s define a few more terms. Kidney function is measured through a blood test known as a serum creatinine. Creatinine is an amino acid byproduct of normal muscle breakdown. (1) Generally speaking, the higher one’s creatinine above normal lab values, the worse the kidney function, because it signifies the kidneys are filtering less blood and clearing less creatinine in the urine. A normal creatinine for an individual will vary based on body size (i.e., due to more or less muscle mass), age, and sex, but for general purposes labs often define a normal creatinine as 0.5-1.2 mg/dL. For a young male a creatinine of 1.2 mg/dL might be normal. However, for someone with active anorexia nervosa binge purge (AN-BP) type, a creatinine of 1.2 mg/dL might represent a significant degree of diminished kidney function. Therefore, interpretation of a creatinine has to be individualized and used in the context of prior creatinine values for that person.
Acute Kidney Injury
The most common cause of acute kidney injury (AKI) as it relates to eating disorders is due to dehydration or overall volume depletion. Eating disorders associated with purging behaviors such as laxative/diuretic use and vomiting will pose the greatest risk for volume depletion and subsequent AKI. Purging behaviors lead to loss of bodily fluids/salts that if not sufficiently replaced will cause a decreased volume of circulating fluid in the blood stream. While the kidneys respond to volume depletion by making changes to try to maximize hydration and maintain blood pressure, in the face of frequent or large enough losses of fluids/salts these adaptations are not enough. As a result, blood flow to the kidneys ultimately decreases, leading to kidney injury and a rise in serum creatinine. If the decreased blood flow is prolonged, it can lead to more severe damage of the kidneys by a process called acute tubular necrosis (ATN). Some may be able to recover full kidney function after an episode of ATN, but others may develop permanent kidney damage leading to chronic kidney disease.
Treatment of acute kidney injury in the setting of volume depletion from purging involves cessation of purging and hydration either orally or with intravenous infusions of saline solution depending on the severity of volume depletion and kidney injury. Rarely, AKI can occur with purely restrictive eating disorders and this most often is in the setting of severely reduced fluid intake in conjunction with restricted food intake.
Chronic Kidney Disease
Chronic kidney disease (CKD) in relation to eating disorders generally develops over a period of years. While there is limited literature at this time exploring this, CKD in eating disorders most commonly develops in the setting of purging behaviors that lead to chronic low blood potassium (hypokalemia) and chronic volume depletion. (2) Both repeated bouts of volume depletion and chronic hypokalemia cause permanent kidney damage. With ongoing behaviors that promote these abnormalities, CKD can progress from stage I (mild) to stage V, or end stage renal disease requiring renal replacement therapy. In my experience, CKD in eating disorders usually develops over a period of years. When the kidney function is so poor that it can no longer balance electrolytes, fluid levels, and remove toxins, medical interventions called renal replacement therapy (because they literally replace the function of the kidneys) such as hemodialysis or peritoneal dialysis are required. Unless an individual receives a kidney transplant, dialysis will be needed for someone with CKD Stage V for the rest of their lives. CKD leading to end stage renal disease and dialysis is often one of the lesser known consequences of chronic purging behaviors, but certainly an important one to be aware of as requiring dialysis can be quite impactful on one’s day-to-day life and general health.
References
1. Gaudiani, JL. Sick Enough: A guide to the medical complications of eating disorders. New York, NY: Routledge, 2019.
2. Bouquegneau A, Dubois BE, Krzesinski JM, Delanaye P. Anorexia nervosa and the kidney. Am J Kidney Dis. 2012 Aug;60(2):299-307. doi: 10.1053/j.ajkd.2012.03.019. Epub 2012 May 19. Review. PubMed PMID: 22609034.