What are the important characters of renal tubular acidosis (RTA) and the diagnostic modalities?

Disorders of renal tubular acidification are due to defects in the reabsorp-tion of bicarbonate (HCO3–), the excretion of hydrogen ion (H+), or both. All types of RTA present with a normal anion gap (hyperchloremic) metabolic acidosis.

They are broadly classified as:

• Proximal RTA or type 2

• Distal RTA or type 1

• Combined proximal and distal RTA or type 3

• Hyperkalemic RTA or type 4. The etiologies of RTA could be varied and result from primary intrinsic renal tubular defects or acquired secondary to other pathologies or drugs. The basic laboratory work-up in any case of suspected RTA would need to include.

• Serum electrolytes and serum bicarbonate, plasma anion gap [Na+–(Cl–+HCO3–)]

• Urinary pH, urinary calcium, urinary creatinine

• Ultrasonography of the kidney to rule out nephrocalcinosis or obstructive

uropathy. Based on these tests further advanced tests to assess renal tubular function may be required.

Osteitis fibrosa cystica, is the term used to describe the classic radiological manifestation of hyperparathyroidism.

• Generalized skeletal demineralization

• Subperiosteal bone resorption with cortical thinning

• Brown tumors (osteoclastomas)—lytic lesions and bone cysts that can disrupt the overlying cortex

• Salt and pepper appearance on skull radiographs