From the Guidelines
The workup for renal tubular acidosis (RTA) should include a comprehensive evaluation starting with basic laboratory tests to confirm metabolic acidosis, including serum electrolytes, arterial blood gas, and urinalysis, as well as urine studies, imaging, and genetic testing as needed, as recommended by the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders 1. The initial assessment should measure serum bicarbonate, anion gap, potassium, chloride, and pH to establish the presence of a non-anion gap metabolic acidosis.
- Urine studies are essential, particularly:
- Urine pH
- Urinary anion gap, which help differentiate between the various types of RTA
- Additional tests include:
- Urine calcium and citrate levels
- Serum calcium, phosphorus, and parathyroid hormone to assess for associated mineral abnormalities
- Imaging studies like ultrasound or CT scan may be indicated to identify nephrocalcinosis or nephrolithiasis, which are common complications of certain RTA types.
- Genetic testing can be valuable in suspected hereditary forms of RTA, as recommended by the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders 1. The diagnosis and management of RTA should be guided by the latest consensus and recommendations from the European Rare Kidney Disease Reference Network Working Group for Tubular Disorders, which emphasizes the importance of a comprehensive evaluation and individualized management plan 1.
- The workup should also consider the patient's medical history, including polyhydramnios, premature birth, growth failure, and family history, as well as biochemical parameters such as serum electrolytes, acid-base status, renin, aldosterone, creatinine, and fractional excretion of chloride 1.
- Renal ultrasound should be performed to detect medullary nephrocalcinosis and/or kidney stones, and genetic counseling should be offered to families with probands with confirmed clinical and/or genetic diagnosis of RTA 1.
From the Research
Diagnosis of Renal Tubular Acidosis
The diagnosis of renal tubular acidosis (RTA) involves assessing urinary acid and bicarbonate secretion to distinguish between distal and proximal RTA 2. In hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia 2.
- The diagnosis of RTA is essentially characterized by normal anion gap and hyperchloremic metabolic acidosis 3.
- RTA can be a primary or secondary defect and results either due to abnormality in bicarbonate ion absorption or hydrogen ion secretion 3.
- Primary defects are common in children due to gene mutation or idiopathic nature while secondary forms are more common in adults 3.
Laboratory Parameters
The following laboratory parameters are essential for making the diagnosis of RTA and excluding the extrarenal causes of hyperchloremic, normal anion gap metabolic acidosis:
- Urinary acid and bicarbonate secretion 2
- Serum potassium concentrations 2
- Urine citrate excretion to determine the risk of nephrolithiasis and calcinosis 4
- Blood reports in correlation with the clinical condition 3
Clinical Approach
A step-wise approach to RTA is necessary, with some understanding of its basic etiopathogenesis 3. This approach helps to have an accurate interpretation of urine and blood reports in correlation with the clinical condition 3.
- Renal tubular acidosis should be suspected in poorly thriving young children with hyperchloremic and hypokalemic normal anion gap metabolic acidosis, with/without syndromic features 4.
- Further workup is needed to determine the type of renal tubular acidosis and the presumed etiopathogenesis, which informs treatment choices and prognosis 4.