Proximal renal tubular acidosis

Introduction of proximal renal tubular acidosis Proximal renal acidosis (PRTA) is also known as type II RTA. The disease is due to the proximal renal tubular reabsorption HCO3-function is defective, renal HCO3-threshold value is reduced, and excessive urine loss of HCO3- causes a decrease in plasma HCO3- concentration resulting in hyperchloric acidosis. basic knowledge The proportion of illness: 0.001% Susceptible people: no special people Mode of infection: non-infectious Complications: metabolic acidosis hypokalemia

Cause of proximal renal tubular acidosis

Genetic (25%):

The cause is unknown, generally considered to be related to heredity, only manifested as HCO3-reabsorption disorder, without other renal tubular and glomerular dysfunction. (1) sporadic babies are temporary; (2) hereditary is persistent, autosomal dominant or autosomal recessive.

Pathogenesis (20%):

Under normal conditions, glomerular filtration of HCO3-99% is reabsorbed, with proximal tubules reabsorbing 80% to 90%, the remaining 2% in the medullary ridge, and 8% in the distal tubule reabsorption, while HCO3- Reabsorption is closely related to the function of H+ secretion by tubular cells. In the small tube, H+-Na+ is exchanged, Na+ is reabsorbed into the cell and combined with HCO3- to form NaHCO3, and then enters the blood, which reserves the alkali reserve for the body, relying on Na+-K+ -ATP enzyme pump activity, proximal tubules reabsorb most of the sodium in the glomerular filtrate, Cl- and water are passively reabsorbed with Na+, in addition, the proximal tubule actively reabsorbs all K+, 2/3 calcium and partial phosphoric acid salt.

PRTA is a proximal renal tubular reabsorption of HCO3-deficiency, HCO-renal threshold is reduced, normal human 25 ~ 26mmol / L, infants 22mmol / L, and PRTA 18 ~ 20mmol / L, when the patient's plasma HCO3- concentration is normal That is, more than 15% of HCO3- is discharged into the urine (only 1% of normal people). Even in mild acidosis, if the concentration of HCO3- in the patient's plasma is still higher than the renal threshold, HCO3- is still discharged to the urine. In the case of severe acidosis, the patient can expel acidic urine.

Due to the reduction of HCO3-reabsorption in the proximal tubules, the Na+-H+ exchange is reduced, Na+ is lost from the urine, causing low sodium, dehydration, and loss of Na+ leads to an increase in secondary aldosterone, resulting in Na+, Cl-retention, plus Increased loss of HCO3-, in order to maintain anion balance, while retaining Cl-, resulting in hyperchloremia, under the action of aldosterone, Na+-K+ exchange and retain Na+, can cause hypokalemia, long-term metabolic acidosis may pass The cause of growth and developmental disorders that hinder the growth or response of growth hormone, leading to the resorption of HCO3-disorder in proximal tubules, is unclear, probably due to immature tubular function development, and in secondary causes, mostly due to internal Raw metabolites or foreign substances are damaged by the proximal tubule epithelium.

With other genetic diseases (10%):

Hereditary diseases associated with other proximal tubular dysfunction, such as idiopathic Fanconi syndrome, cystine disease, ocular-brain-renal syndrome (Lowe syndrome), hereditary fructose intolerance, Tyrosinemia, galactosemia, glycogen storage disease, mitochondrial myopathy, metachromatic leukodystrophy, etc.

Drug and toxin kidney damage (10%):

Such as carbonic anhydrase inhibitors, expired tetracycline, methyl 3-chromone, maleic acid poisoning, heavy metal (calcium, lead, copper, mercury) poisoning.

Other (10%):

Such as subacute necrotizing encephalomyelopathy (Leigh syndrome), tetralogy of Fallot, intestinal malabsorption, hyperparathyroidism, renal cyst disease, hereditary nephritis, chronic renal allograft rejection, multiple myeloma, Sjögren Syndrome, amyloidosis, chronic active hepatitis, recurrent renal calculi, renal medullary cystic disease, Wilson's disease, etc.

Proximal renal tubular acidosis prevention

Primary patients have unclear etiology and no reliable prevention methods. Clinically, they mainly give positive prevention and treatment to patients with kidney and kidney damage caused by drugs and toxins, such as intestinal malabsorption and hyperthyroidism, to prevent metastatic acidosis. Causes systemic metabolic disorders and impaired kidney function.

Proximal renal tubular acidosis complications Complications, metabolic acidosis, hypokalemia

Nutritional disorders, metabolic acidosis, hypokalemia, rickets, growth retardation.

Symptoms of proximal renal tubular acidosis Common symptoms Polyuria uric acid abnormal appetite loss nausea constipation Dehydration nausea and vomiting weak kidney area dull pain bone pain

The symptoms of this disease are usually mild, manifested as growth retardation, malnutrition, lack of ease, weakness, anorexia, polyuria, polydipsia or hypokalemia, typical cases of hyperchlorinemia, but distal renal tubular acidification Normal function, urine pH can be reduced to below 5.5, or accompanied by bone damage (osteomalacia, osteoporosis), diabetes, amino acid urine, etc. The main clinical features of type II PRTA are:

Primary PRTA is mainly seen in male infants, and many other proximal tubule reabsorption defects such as diabetes, phosphorus, etc., spontaneously disappear in 1 to 2 years old.

Patients with metabolic acidosis and low sodium, hypokalemia may have growth retardation, nausea, vomiting and other acidic poisoning and weakness, fatigue, muscle weakness, constipation and other hyponatremia and hypokalemia, due to HCO3- The renal threshold decreased to 15-18 mmol/L at PRTA, and acidic urine (pH <5.5) was discharged after 15 mmol/L. Severe acidosis was rare.

In addition, if there is no high-phosphorus urinary disease with proximal tubule phosphorus absorption disorder, and there are few metabolic bone diseases, renal calcification, kidney stones, but non-selective patients, there may be increased urinary phosphorus, glucoseuria, amino aciduria. Wait.

In addition to the above-mentioned performance, secondary PRTA also has the symptoms of primary disease, and is easily covered by the symptoms of the primary disease. It should be alert to the occurrence of secondary PRTA.

Proximal renal tubular acidosis

1. Blood biochemical examination of plasma HCO3- and pH decreased, hyperchloremia, sodium, potassium normal or decreased.

2. Urine check urine pH can be alkaline or acidic according to blood HCO3-level, 24h urine HCO4- only titratable acid is normal, urinary calcium can be increased or normal (measuring urine PCO2 can be injected into NaHC03 to make urine alkalized, when When urine pH>blood pH, urine PCO2>blood PCO2, 2.66 kPa or more is diagnostic.)

3. Urinary cystine examination of cysteine urine in the case of proximal convoluted tubule disease, such as positive is helpful for diagnosis (cyanide nitrohydrocyanate test: take 5ml of urine and 1 drop of concentrated ammonia, 5% cyanide 3 drops of sodium, positive for purple-red reaction).

4. For the acid load test method, see Type I RTA. In the acid load test, if the urine pH is <5.5 or lower, the type II RTA is diagnosed.

5. Alkali load test:

(1) Oral sodium bicarbonate method: starting from 1mmol / (kg · d), daily increase to 10mmol / (kg · d), acidosis is corrected, blood test, urine HCO3- concentration and glomerular filtration Over-rate, calculate the percentage of urinary HCO3-: HCO3- in urine = urine HCO3-(mmol/L) × urine volume (ml/min) / plasma HCO3-(mmol/L) × GFR, normal human urine HCO3- Zero; type II, mixed RTA > 15%, type I RTA < 3% to 5%.

(2) Intravenous instillation of sodium bicarbonate method: 5% NaHCO3 was instilled at a rate of 4 ml/min for 2 h, and blood pH, PCO2, HCO3-concentration and urine pH, HCO3-concentration were measured before injection; After 30,90 min, the blood pH, PCO2, and HCO3-concentration were measured; at 60, 120 min, the urine pH and HCO3-concentration were measured. When the patient's blood HCO3-concentration returned to normal, the urine HC03-excretion amount was 15% of the glomerular filtration excess. , suggesting HCO3-absorption disorder in the proximal convoluted tubule, urinary HCO3-excretion fraction = (urinary HCO3-/plasma HCO3-)/(urine creatinine/creatinine), plasma HCO3-concentration is normal, type II RTA HCO3-excretion score>15 %, type I RTA < 5%, this method can identify type I, type II RTA.

Regular electrocardiogram, imaging examination and B-ultrasound examination.

Diagnosis and diagnosis of proximal renal tubular acidosis

Diagnostic criteria

This type is more common in male children. It occurs in childhood, some of which are relieved with age. The symptoms are usually mild, showing growth retardation, malnutrition, lack of ease, weakness, anorexia, polyuria, polydipsia, or hypokalemia. Symptoms, typical cases of hyperchloric acidemia, but the distal renal tubular acidification function is normal, urine pH can be reduced to below 5.5, or bone damage (osteomalacia, osteoporosis), diabetes, amino acid urine, etc., according to the above performance And laboratory examination and diagnosis can be established, if necessary, for bicarbonate reabsorption test and renal HCO3-threshold determination, such as urinary HCO3-excretion rate of more than 15% of the filtration excess can be confirmed.

Diagnostic points for type II RTA:

1. Patients with non-renal diseases, such as hyperchloremic acidosis, such as metabolic acidosis (plasma HCO3-<1518mmol/L, morning urine pH5.5, NH+4 displacement>40mol/( Min·1.73m2), and exclude HCO3- from the gastrointestinal tract, can diagnose the disease.

2. Unexplained hypokalemia, hypophosphatemia, urine glucose positive, elevated urinary potassium, elevated urinary phosphorus and hyperuricuria.

3. Urine pH>6.0.

4. Acid, alkali load test is positive.

Differential diagnosis

1. Identification of other diseases caused by acidosis caused by nitrogen retention, such as diarrhea, ketoacidosis and the like.

2. Identification with other types of renal tubular acidosis, especially should be differentiated from type I.

The main clinical manifestation of this disease is hyperchloremia metabolic acidosis. The growth retardation of young children is often the most important or even the only manifestation of this disease. Therefore, children with developmental delay should pay close attention to the presence or absence of PRTA. In case of uncorrectable dehydration and acidosis, you should be alert to the possibility of this disease, and check accordingly, the amount of bicarbonate or citrate buffer must be 6mmol / (kg · d) to maintain plasma CO2 binding capacity 22mmol / L, this point can be distinguished from the distal RTA, urine concentration dysfunction is lighter than the distal RTA.

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