Renal tubular acidosis (RTA) and kidney stones: Diagnosis and management.

Renal tubular acidosis (RTA) is a set of raredis orders in which the renal tubule is unable to excreteacid normally and there by maintain normal acid-basebalance, resulting in a complete or incomplete metabolicacidosis. In distal RTA (dRTA, also known as classicalor type 1 RTA), there is a defect in excreting H+ ionsalong the distal nephron (distal tubule and collectingduct), leading to an alkaline urinary pH with calcium phosphate precipitation and stones. Causes of dRTAinclude genetic mutations, autoimmune disease, and some drugs.Clinical manifestations of the genetic forms of dRTA typically occur during childhood and may vary from mildclinical symptoms, such as a mild metabolic acidosis, hypokalaemia,and incidental detection of kidney stones, to more serious manifestations such as failure to thrive,severe metabolic acidosis, rickets and nephrocalcinosis.Progressive hearing loss may develop in patients withrecessive dRTA, which, depending the causative genemutation, can be present at birth or develop later in adolescence or early adulthood. Diagnosis of dRTA can be challenging, since it requires a high index of suspicion and/or measurement of urinary pH after an acid load, usually in the form of oral ammonium chloride; this should normally acidify the urine to pH below 5.3. In dRTA, urinary citrate levels a real so low and patients are at increased risk of for mingkidney stones from a combination of alkaline urine and low citrate. Ideally, affected patients need regular outpatient follow-up by a urologist and nephrologist. Thus, any patient found to have a calcium phosphate kidney stone, low urinary citrate, and raised urinary pH, especially with an early morning pH >5.5, should be evaluated for underlying dRTA. Patients with complete dRTA will have a low (<20 mmol/L) plasma or serum bicarbonate concentration, whereas in those with incomplete dRTA, bicarbonate levels are usually normal. Oral alkali as potassiumcitrate is still the mainstay of treatment in dRTA.