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 ¹ (Maher and Scoble, 1989).
• Persistent hyperchloraemia and a low serum bicarbonate level despite normal kidney function, reflecting impaired acid excretion or bicarbonate reabsorption ¹ (Laing and 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 ¹ (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 ¹ (Laing and Unwin, 2006).
• Recurrent nephrolithiasis or nephrocalcinosis on imaging, often associated with distal RTA due to impaired acidification of urine ¹ (Maher and 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 ¹ (Maher and Scoble, 1989; Laing and Unwin, 2006; Alonso-Varela et al., 2020).