Overview.
This syndrome is characterized by decreased reabsorption of bicarbonate in the proximal tubule, resulting in a decrease of this salt in the blood and a hyperchloremic acidosis. As the reabsorption of bicarbonate by the proximal tubule decreases, the bicarbonate reaching the distal renal tubule increases, and if the absorption threshold of the latter is exceeded, the urinary bicarbonate increases and the urinary pH rises; if the blood bicarbonate decreases to a certain degree, and the tubule is able to completely absorb the bicarbonate in the glomerular filtrate, the urine can be restored to be acidic, and the urinary pH can decrease. In addition, the proximal renal tubules can also decrease glucose, phosphate, uric acid, amino acid reabsorption, and manifest as Fanconi syndrome.
Etiology
1. Primary
Familial or sporadic.
2.Other hereditary diseases
Hepatomegaly, carbonic anhydrase deficiency, cystinosis and lowe’s syndrome (brain-eye-kidney syndrome).
3. Drugs and poisons
Such as lead, cadmium, mercury, copper and other poisoning, long-term application of carbonic anhydrase inhibitors, failure of tetracycline, injection of arginine, lysine and so on.
4. Other diseases
Such as hyperparathyroidism, multiple myeloma, dry syndrome, autoimmune hepatitis, transplantation of kidney rejection reaction, vitamin D excess.
Symptoms
The lesions are mostly in male children, often with hyperchloremic metabolic acidosis, mostly accompanied by hypokalemia, with muscle weakness, polyuria, irritable thirst, and polydipsia. Long-term chronic hyperchloremic metabolic acidosis can lead to pediatric malnutrition and growth retardation. Due to the normal function of distal renal tubules, urine acidification function is good, and urine pH can be reduced to below 5.5. Type II hypocalcemia and hypophosphatemia are much milder than type I, so the incidence of renal stones or renal calcification is low. Secondary individuals often have renal glycosuria and renal aminoaciduria, manifesting as Fanconi syndrome.
Examination
1. Urine PH value measurement
2.X-ray examination
To detect osteoporosis, pathologic fracture or urinary stones.
3. Urinary H2CO3-excretion rate measurement (sodium carbonate loading test)
Urinary H2CO3-excretion rate measurement (sodium carbonate loading test) is required to confirm the diagnosis. Oral method: daily oral sodium bicarbonate until plasma CO2 binding capacity is normalized, then plasma and urine H2CO3- and creatinine (Cr) are measured.
Diagnosis.
Renal tubular acidosis can be diagnosed if the urinary pH is >6 based on the above typical clinical manifestations, excluding other causes of metabolic acidosis, and the diagnosis should be established by: ① the urinary pH will not be lower than 5.5 even in severe acidosis, ② there are significant disturbances in calcium and phosphorus metabolism as well as skeletal alterations, ③ there is a significant decrease in urinary ammonium, ④ the fractional excretion of HCO3- by filtration (FEHCO3-) is <5%, and ⑤ the Positive ammonium chloride loading test. Most common in children, often accompanied by low blood phosphorus, low uric acid, amino aciduria and nephrogenic glycosuria. The diagnosis is confirmed by low blood pH and urinary excretion of large amounts of bicarbonate even after sodium bicarbonate infusion.
Treatment
1. Prevent the factors that induce the exacerbation of the disease.
2. Correct acidosis; sodium bicarbonate can be given orally or by IV. Sodium bicarbonate can be given orally or intravenously. Compound sodium citrate can also be given.
3. If there is hypokalemia, 10% potassium citrate can be given.
4. Calcitriol can be given to those with severe bone disease, and changes in blood calcium should be noted.