Urate crystal in a soy-based formula-fed infant: An unusual clinical presentation

Soy-based infant formula may cause isolated hyperuricosuria in infants who consume it as their primary source of nutrition. Soy-based infant formula contains purine, which is converted to uric acid, and two-thirds of the uric acid is eliminated through the kidneys, resulting in hyperuricosuria, which can lead to nephrolithiasis if consumed in excess. A 7-month-old boy who had been consuming soy-based formula since birth presented with his first episode of red crystal during urination. He didn't have any other symptoms. The fractional excretion of uric acid was 35%, which was excessive, nevertheless his serum uric acid level was normal. The ultrasound of Kidney, Ureter and Bladder revealed no nephrolithiasis. He had been treated with potassium citrate to alkalinize his urine and was recommended to switch to cow-based formula milk. After a few weeks of consuming cow-based formula, his urine was clear. Soy-based infant formula can cause isolated hyperuricosuria without inducing nephrolithiasis. Nonetheless, it is critical to rule out secondary causes of hyperuricosuria in infants as soon as symptoms appear. Most of infants with isolated hyperuricosuria are asymptomatic but can cause long term effect of nephrolithiasis which need regular monitoring