Renal tubular acidosis

Renal tubular acidosis - metabolic, GFR, as a rule, is not changed.

[1], [2], [3], [4], [5], [6], [7]

Causes of the renal tubular acidosis

Proximal renal tubular acidosis is formed with a decrease in the ability of epithelial cells to reabsorb bicarbonates. Observed isolated or in the framework of Fanconi syndrome (primary and secondary) proximal renal tubular acidosis.

Isolated proximal renal tubular acidosis is due to a genetically determined decrease in the activity of carbonic anhydrase or is associated with a prolonged intake of acetazolamide.

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

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.

Perhaps the inheritance of distal renal tubular acidosis in an autosomal dominant type (Albright-Butler syndrome).

With many diseases, secondary distal tubular acidosis develops. As a rule, hypercalciuria and hypokalemia do not occur.

Secondary distal tubular acidosis is observed with:

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

Possible development of distal renal tubular acidosis with hyperkalemia. Most of its variants are associated with absolute or relative deficiency of aldosterone.

[8], [9], [10], [11],

Symptoms of the renal tubular acidosis

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

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

Symptoms of Albright-Butler syndrome - lag in growth, severe muscle weakness,  polyuria, rickets (in adults - osteomalacia), nephrocalcinosis and nephrolithiasis. The first symptoms of the disease, as a rule, develop in early childhood, but the cases of its debut in adults are described.

Forms

Isolate the proximal and distal variants of renal tubular acidosis.

Variants of distal renal tubular acidosis with hyperkalemia

Cause of acidosis	Disease
Deficiency of mineralocorticoids	Combined mineral and glucocorticosteroid insufficiency Addison's disease Bilateral adrenalectomy Destruction of adrenal tissue (hemorrhage, swelling) Congenital defects of adrenal enzymes Deficiency of 21-hydroxylase Deficiency of 3b-hydroxydihydrogenase Deficiency of cholesterol-monooxygenase Isolated aldosterone insufficiency Family deficiency of methyloxidase Chronic idiopathic hypoaldosteronism Transient hypoaldosteronism of childhood Drugs (heparin sodium, ACE inhibitors)
Giporeninemic hypoalldosteronism	Diabetic Nephropathy Tubulo-interstitial nephropathies Obstructive uropathy Sickle cell anemia Nonsteroidal anti-inflammatory drugs
Pseudohypoaldosteronism	Primary pseudohyperdosteronism Receiving spironolactone

[12], [13], [14]

Diagnostics of the renal tubular acidosis

Laboratory diagnostics of renal tubular acidosis

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

In connection with the increase in sodium excretion (in the 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, hypercalciuria is observed.

Diagnosis of renal tubular acidosis (distal form) consists in using a test with ammonium chloride or calcium chloride - urine pH is not lower than 6.0. At pH values <5,5 distal tubular acidosis should be excluded.

[15], [16], [17], [18], [19], [20]

Treatment of the renal tubular acidosis

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

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