The answer to whether dialysis removes uric acid is yes. Dialysis replaces the function of failing kidneys, which can no longer adequately remove waste products like uric acid from the bloodstream. Uric acid is a natural byproduct of purine metabolism, compounds found in many foods and produced by the body. When kidney function declines, this waste product accumulates, leading to hyperuricemia, which dialysis is designed to correct.
The Role of Kidneys in Uric Acid Regulation
Uric acid is the final product of purine breakdown, a process that occurs continuously in the body. Healthy kidneys maintain a stable concentration of uric acid in the blood by filtering and excreting it in the urine. Almost all serum urate is initially filtered by the glomeruli, but a significant portion (approximately 91–95%) is reabsorbed back into the blood in the proximal tubules.
Only a small fraction of the filtered urate (about 3–10%) is ultimately excreted. When a person develops chronic kidney disease (CKD) or end-stage renal disease (ESRD), the kidneys’ ability to filter and excrete this substance is severely compromised. This reduced renal clearance causes uric acid levels to rise in the blood, resulting in hyperuricemia. Intervention, often through dialysis, is necessary to prevent complications like gout.
How Dialysis Removes Uric Acid
Dialysis removes uric acid because it is a relatively small molecule (approximately 168 Daltons). The primary removal mechanism for small molecules is diffusion. During dialysis, the patient’s blood flows on one side of a semipermeable membrane, and a specialized fluid called dialysate flows on the other side.
The dialysate is formulated to have a zero or very low concentration of waste products, including uric acid, creating a concentration gradient. This gradient causes the uric acid, which is highly concentrated in the blood, to move across the membrane into the dialysate. This passive movement continues until the concentration gradient is reduced, effectively clearing the toxin from the blood. Convection, or solvent drag, also contributes to removal, especially in high-flux dialysis where fluid is pulled across the membrane.
Efficiency Differences Between Hemodialysis and Peritoneal Dialysis
The two main types of dialysis, hemodialysis (HD) and peritoneal dialysis (PD), both remove uric acid but at different rates. Hemodialysis, typically performed three times a week, is highly efficient at rapidly clearing small molecules. High blood flow rates and the large surface area of the dialyzer membrane allow for a substantial and immediate reduction in uric acid levels during each session. Rapid clearance via HD is often preferred to quickly lower dangerous levels, such as in acute uric acid nephropathy.
Peritoneal dialysis, in contrast, provides a continuous, slower form of clearance. This method uses the patient’s peritoneal membrane as the filter, with the dialysate remaining in the abdominal cavity for several hours. Although the total clearance rate per unit of time may be lower than HD, the continuous nature of PD often results in more stable uric acid levels overall.
Managing Uric Acid Levels Between Treatments
Since dialysis treatments are intermittent, uric acid levels inevitably rebound between sessions as the body continues production. Therefore, managing uric acid requires interventions beyond the treatment time itself. Dietary modifications, particularly adopting a low-purine diet, are an important component of this management plan.
Patients are advised to limit or avoid purine-rich foods, such as organ meats, certain seafood, and high-fructose corn syrup, as these metabolize into uric acid. Maintaining adequate hydration is also important, as sufficient fluid intake assists residual kidney function in excreting remaining waste. When hyperuricemia or gout is present, pharmacological agents are necessary to reduce production. Xanthine oxidase inhibitors like allopurinol or febuxostat are commonly prescribed to lower uric acid levels by blocking the enzyme responsible for its creation. These medications may require careful dosage adjustments in patients with impaired kidney function.