Renal tubular acidosis.

Renal tubular acidosis is metabolic, the SCF is usually unchanged.

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Causes renal tubular acidosis.

Proximal renal tubular acidosis develops when the ability of epithelial cells to reabsorb bicarbonates decreases. Isolated proximal renal tubular acidosis or proximal renal tubular acidosis is observed within the Fanconi syndrome (primary and secondary).

Isolated proximal renal tubular acidosis is caused by a genetically determined decrease in carbonic anhydrase activity or is associated with long-term use of acetazolamide.

Distal renal tubular acidosis develops in the absence of secretion of hydrogen ions into the lumen of the distal tubule or an increase in their uptake by the epithelial cells of this segment of the nephron.

Another mechanism of formation is a decrease in the availability of urinary buffers, primarily ammonium ions, with a decrease in their formation or excessive accumulation in the interstitium.

Distal renal tubular acidosis may be inherited in an autosomal dominant manner (Albright-Butler syndrome).

In many diseases, secondary distal renal tubular acidosis develops. Hypercalciuria and hypokalemia usually do not occur.

Secondary distal renal tubular acidosis is observed in:

• hypergammaglobulinemia;
• cryoglobulinemia;
• Sjogren's disease and syndrome;
• thyroiditis;
• idiopathic fibrosing alveolitis;
• primary biliary cirrhosis;
• systemic lupus erythematosus;
• chronic active hepatitis;
• primary hyperparathyroidism;
• vitamin D intoxication;
• Wilson-Konovalov disease;
• Fabry disease;
• idiopathic hypercalciuria;
• hyperthyroidism;
• taking medications (amphotericin B);
• tubulointerstitial nephropathy (endemic Balkan nephropathy, obstructive uropathy);
• renal transplant nephropathy;
• cystic kidney diseases (medullary sponge kidney, medullary cystic kidney disease);
• hereditary diseases (Ehlers-Danlos syndrome, sickle cell anemia).

Distal renal tubular acidosis with hyperkalemia may develop. Most of its variants are associated with absolute or relative aldosterone deficiency.

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Symptoms renal tubular acidosis.

Symptoms of renal tubular acidosis (proximal form) are often absent.

Symptoms of renal tubular acidosis (distal form) are caused by loss of calcium in the urine, often accompanied by rickets-like changes in bones, osteomalacia, pathological fractures are possible. Alkaline urine reaction with increased calcium concentration in it predisposes to calcium nephrolithiasis.

Signs of Albright-Butler syndrome are growth retardation, severe muscle weakness, polyuria, rickets (osteomalacia in adults), nephrocalcinosis and nephrolithiasis. The first symptoms of the disease usually develop in early childhood, but cases of its debut in adults have also been described.

Forms

There are proximal and distal variants of renal tubular acidosis.

Variants of distal renal tubular acidosis with hyperkalemia

Cause of acidosis	Disease
Mineralocorticoid deficiency	Combined mineralo- and glucocorticosteroid deficiency Addison's disease Bilateral adrenalectomy Destruction of adrenal tissue (hemorrhage, tumor) Congenital defects of adrenal enzymes 21-hydroxylase deficiency 3b-hydroxydihydrogenase deficiency Cholesterol monooxygenase deficiency Isolated aldosterone deficiency Familial methyl oxidase deficiency Chronic idiopathic hypoaldosteronism Transient hypoaldosteronism of childhood Medicines (sodium heparin, ACE inhibitors)
Hyporeninemic hypoaldosteronism	Diabetic nephropathy Tubulointerstitial nephropathy Obstructive uropathy Sickle cell anemia Nonsteroidal anti-inflammatory drugs
Pseudohypoaldosteronism	Primary pseudohypoaldosteronism Taking spironolactone

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Diagnostics renal tubular acidosis.

Laboratory diagnostics of renal tubular acidosis

In proximal renal tubular acidosis, significant bicarbonaturia, hyperchloremic acidosis, and an increase in urine pH are detected.

Due to the increased excretion of sodium (as part of sodium bicarbonate), secondary hyperaldosteronism with hypokalemia often develops.

In distal renal tubular acidosis, in addition to severe systemic acidosis, a significant increase in urine pH, hypokalemia, and hypercalciuria are observed.

Diagnosis of renal tubular acidosis (distal form) involves using a test with ammonium chloride or calcium chloride - urine pH is not lower than 6.0. At pH values <5.5, distal renal tubular acidosis should be excluded.

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Treatment renal tubular acidosis.

Treatment of renal tubular acidosis (proximal form) consists of using large doses of sodium bicarbonate. It is also possible to use citrate mixtures. It is advisable to combine sodium bicarbonate with thiazide-like diuretics, however, the latter sometimes aggravate hypokalemia - in these cases, simultaneous administration of potassium preparations is necessary.

Treatment of renal tubular acidosis (distal form) consists of administration of bicarbonates. Renal tubular acidosis with hyperkalemic variants requires administration of mineralocorticoids and loop diuretics.