What are the key clinical features that suggest a diagnosis of renal tubular acidosis in a patient?

Key clinical features suggesting a diagnosis of renal tubular acidosis (RTA) include:

• Non-anion gap metabolic acidosis with a normal or near-normal glomerular filtration rate, indicating a primary tubular defect rather than glomerular disease NICE NG203 Maher & Scoble 1989.
• Persistent hyperchloraemia and a low serum bicarbonate level despite normal kidney function, reflecting impaired acid excretion or bicarbonate reabsorption NICE NG203 Laing & Unwin 2006.
• Urinary findings such as an inappropriately high urine pH (>5.5 in distal RTA) despite systemic acidosis, or low urine citrate, which predispose to nephrocalcinosis and kidney stones NICE NG203 Alonso-Varela et al. 2020.
• Clinical manifestations including growth retardation in children, muscle weakness, polyuria, and symptoms related to hypokalaemia (e.g., muscle cramps, arrhythmias) especially in distal RTA NICE NG203 Laing & Unwin 2006.
• Recurrent nephrolithiasis or nephrocalcinosis on imaging, often associated with distal RTA due to impaired acidification of urine NICE NG203 Maher & Scoble 1989.
• In children, incomplete distal RTA may present subtly with failure to thrive or mild metabolic acidosis without overt systemic symptoms, requiring a high index of suspicion Alonso-Varela et al. 2020.

Overall, the diagnosis is suggested by a combination of biochemical evidence of a normal anion gap metabolic acidosis, characteristic urinary abnormalities, and clinical features such as growth failure, hypokalaemia symptoms, and nephrocalcinosis NICE NG203 Maher & Scoble 1989Laing & Unwin 2006Alonso-Varela et al. 2020.