The pH of urine—its alkalinity or acidity—reflects the kidneys’ ability to maintain a normal hydrogen ion concentration in plasma and extracellular fluids. The normal hydrogen ion concentration in urine varies, ranging from pH 4.6 to 8.0, but it usually averages around pH 6.0.

The simplest procedure for testing the pH of urine consists of dipping a reagent strip (such as Combistix) into a fresh specimen of the patient’s urine and comparing the resultant color change with a standardized color chart.

An alkaline pH (above 7.0), resulting from a diet low in meat but high in vegetables, dairy products, and citrus fruits, causes turbidity and the formation of phosphate, carbonate, and amorphous crystals. Alkaline urine may also result from urinary tract infection and from metabolic or respiratory alkalosis.

An acid pH (below 7.0), resulting from a high-protein diet, also causes turbidity as well as the formation of oxalate, cystine, amorphous urate, and uric acid crystals. Acid urine may also result from renal tuberculosis, phenylketonuria, alkaptonuria, pyrexia, diarrhea, starvation, renal failure, and all forms of acidosis. Low urine pH is also associated with insulin resistance and metabolic syndrome.¹

Measuring urine pH can also help monitor some medications—such as methenamine, ammonium chloride, and some diuretics—that are active only at certain pH levels.