Acidic Urine pH in Gout Patients Associated With Increased Risk of Kidney Stones

Nephrolithiasis, otherwise known as kidney stones, are crystal concretions typically formed in the kidney. The formation of kidney stones has been shown to be strongly influenced by urinary pH levels. Urine pH levels that are more alkaline (pH >8) favor the crystallization of calcium- and phosphate-containing stones, while acidic urine pH (pH <5.5) promote uric acid or cystine stones.

Gout, the highly prevalent form of inflammatory arthritis, is commonly associated with elevated levels of uric acid, low urinary pH, chronic kidney disease (CKD), and increased risk of CKD progression.

Despite the extensive research conducted on gout, the potential relationship of acidic urine pH to broader manifestations of kidney disease in gout is still poorly understood. A study, published in Arthritis Research & Therapy, sought “to identify the distribution of urine pH values in gout patients and to test the hypothesis that acidic urine pH is an independent risk factor for renal alterations in gout patients.”

Conducting a population-based cross-sectional study, researchers examined 3,565 gout patients to investigate the association between low urinary pH and kidney disease. Patients were sorted into subgroups based on urine pH levels (≤5.0, >5.0-5.5, >5.5-6.2, >6.2-6.9, and >6.9). Following an assessment from their primary clinicians to determine the safety, all patients underwent 2 weeks of medication cessation and a 3-day standardized metabolic diet. Urine pH, estimated glomerular filtration rate (eGFR), nephrolithiasis, renal cysts, microhematuria (blood in the urine), and proteinuria (elevated levels of protein in the urine) were measured and compared between groups.

Overall, 46.5% of patients had acidic urine. The median urine pH and eGFR of all patients was 5.63 and 98.32, respectively. The prevalence of nephrolithiasis, microhematuria, and proteinuria were 16.9%, 49.5%, and 6.9%, respectively.

Multivariable analysis showed that eGFR was associated with age, sex, diastolic blood pressure, serum uric acid, hypertension, diabetes, and urine pH. Additionally, acidic urine pH, particularly urine pH <5.0, was significantly associated with the prevalence of kidney disease, nephrolithiasis, kidney cyst, and microhematuria.  Patients with a pH level between 6.2 and 6.9 had the highest eGFR and lowest prevalence of nephrolithiasis, microhematuria, and proteinuria.

“Our results support further, prospective clinical investigations into the potential benefits of urine alkalization in gout patients with acid urine and hyperuricemia,” the researchers wrote.