Type II renal tubular acidosis

　　The etiology of type II renal tubular acidosis mainly includes:
　　Primary:Familial or sporadic.
　　Other genetic diseases:Hemochromatosis, carbonic anhydrase deficiency, cystinosis, and Lowe syndrome (brain-eye-kidney syndrome).
　　Drugs and toxins:Such as lead, cadmium, mercury, copper, and other poisoning, long-term use of carbonic anhydrase inhibitors, expired tetracycline, injection of amino acids, lysine, and others.
　　Other diseases:Such as hyperparathyroidism, multiple myeloma, Sjogren's syndrome, autoimmune hepatitis, rejection reaction of transplanted kidney, vitamin D overdose, and others.

　　Due to the prolonged time of glucose, phosphate, uric acid, and amino acid reabsorption in the proximal renal tubules being below normal levels, the complications of type II renal tubular acidosis mainly include systemic malnutrition, hypokalemia, osteomalacia, and growth and development delay.

　　The symptoms of this disease are usually mild, manifested as growth delay, malnutrition, fatigue, weakness, anorexia, polyuria, thirst, or hypokalemia. Typical cases have hyperchloremia; but the acidification function of the distal renal tubules is normal, and urine pH can drop below 5.5, or be accompanied by bone damage (osteomalacia, osteoporosis), diabetes, aminoaciduria, and other symptoms. The main clinical characteristics are:
　　Primary PRTA (Renal tubular acidosis. ）It is mainly seen in male infants, often accompanied by other proximal renal tubular reabsorption dysfunction, such as diabetes and phosphaturia, which can spontaneously disappear at 1 to 2 years of age. Children may experience growth and development delay, nausea, vomiting, and other symptoms of acidosis, as well as weakness, fatigue, muscle weakness, constipation, and other symptoms of hyponatremia and hypokalemia due to metabolic acidosis and hyponatremia and hypokalemia. Severe acidosis is rare.
　　In addition, without proximal tubular phosphorus absorption disorder, there is no hyperphosphatemia, and metabolic bone disease, renal calcification, and renal calculi are rarely seen. Non-selective patients may present with increased urinary phosphorus, glucosuria, aminoaciduria, and other symptoms.
　　Secondary PRTA, in addition to the above symptoms, also has symptoms of the primary disease, and is often masked by the symptoms of the primary disease.

　　Primary cases due to unknown causes have no reliable preventive methods. Clinically, primary prevention and treatment are mainly given to those with secondary renal damage due to drugs and toxins, and other diseases such as malabsorption of the intestines and hyperthyroidism, in order to prevent metabolic acidosis from extending and causing systemic metabolic disorder and renal damage. Active treatment of the primary disease and complications is carried out, and calcium and active vitamin D preparations can be given when bone disease or severe calcium deficiency occurs.

　　The main laboratory examinations for type II renal tubular acidosis are:
　　Laboratory examination
　　1. Blood biochemical examination Plasma HCO3- and pH decrease, hyperchloremia, sodium and potassium are normal or decreased.
　　2. Urinalysis Urine pH can be alkaline or acidic according to the blood HCO3- level. 24-hour urine HCO4- can only be titrated with normal acid, and urinary calcium can be increased or normal (NaHCO3 can be injected into the urine to alkalinize it when measuring urinary PCO2, when urine pH is higher than blood pH, urine PCO2 is higher than blood PCO2, 2.66 kPa or more has diagnostic significance).
　　3. Urinary cystine examination Cystinuria often exists in proximal tubular diseases, and if positive, it is helpful for diagnosis (cyanide nitroprusside test: take 5 ml of urine and add 1 drop of concentrated ammonia water, 3 drops of 5% sodium cyanide, and a purple-red reaction is positive).
　　4. Acid load test In the acid load test, if the urine pH　　5. Alkaline load test Oral sodium bicarbonate method: Starting from 1 mmol/(kg·d), the dose is increased day by day to 10 mmol/(kg·d). After the acidosis is corrected, measure the blood and urine HCO3- concentrations and glomerular filtration rate, and calculate the percentage of urinary HCO3-: Urinary HCO3- amount = Urinary HCO3- (mmol/L) × Urine volume (ml/min) / Plasma HCO3- (mmol/L) × GFR. Normal urine HCO3- is zero; type II, mixed PRTA > 15%, type I PRTA　　Other auxiliary examinations
　　Routine electrocardiogram, imaging examination and B-ultrasound examination.

　　The diet of patients with type II renal tubular acidosis should mainly be light, to a certain extent reducing the burden on the kidneys; alkaline foods, potassium-rich foods (watermelon, oranges), and foods containing vitamin D (cod liver oil) are preferred.

　　Drug treatment for type II renal tubular acidosis:
　　1. Eliminate the primary factors.
　　2. Correct acidosis with NaHCO3: Due to the increased concentration of blood HCO3- after taking the medicine, the excretion of HCO3- in urine also increases, so a larger dose of Na is required.
　　HCO3, generally 5-10 mEq/kg per day, and some may reach 15 mEq/kg or more per day. In severe cases, diuretics such as hydrochlorothiazide and restriction of sodium intake can be used to reduce the excretion of urinary HCO3-.
　　3. Potassium supplementation: The increase in the excretion of HCO3- in urine will exacerbate the loss of urinary K+, so attention should be paid to potassium supplementation.
　　4. Supplement should also be given when there are signs of vitamin D deficiency.