Mixed renal tubular acidosis

Introduction to mixed renal tubular acidosis Hybrid RTA is a combination of the clinical features of the two types of I and II RTAs described above. Some people have divided this type into mixed type and type III RTA. The clinical features of both mixed type I and type II RTAs are considered to be subtypes of type II RTA. basic knowledge The proportion of illness: 0.03%--0.05% Susceptible people: no specific population Mode of infection: non-infectious Complications: metabolic acidosis, hypokalemia, vitamin D deficiency, kidney stones, uremia, neurological deafness

Causes of mixed renal tubular acidosis

(1) Causes of the disease

Hybrid RTA is a combination of the clinical features of both types I and II RTAs, so the cause of the disease is also characterized by type I and II RTA.

1. Primary disease: sporadic and hereditary.

2. Secondary hereditary diseases: osteopenia, neurological deafness, carbonic anhydrase B deficiency or decreased function, lack of pyruvate hydroxylase, hereditary fructose tolerance, cystineosis, Lowe syndrome, Wilson is sick.

3. Drugs and poisoning: amphotericin B, lithium, toluene.

4. Abnormal calcium metabolism: primary calcium deposition nephropathy, idiopathic hypercalcemia, excessive vitamin D or poisoning, hyperthyroidism, hyperparathyroidism.

5. Systemic immune diseases and high gamma globulin diseases: idiopathic hypergammaglobulinemia, multiple myeloma, systemic lupus erythematosus, Sjogren's syndrome, thyroiditis, cirrhosis, primary biliary sclerosis , chronic active hepatitis.

6. Interstitial renal disease: obstructive nephropathy, renal transplant rejection, sickle cell hemoglobin disease, sponge kidney, analgesic nephropathy.

7. Primary disease: sporadic, hereditary.

8. Secondary hereditary disease: Hereditary fructose content decreased, carbonic anhydrase B deficiency and decreased function.

9. Drugs and poisons: heavy metals (lead, cadmium, mercury, copper), carbonic anhydrase inhibitors, taking expired tetracycline.

10. Others: hyperparathyroidism, multiple myeloma, Sjogren's syndrome, amyloidosis, nephrotic syndrome, renal transplant rejection, hypervitamin D, chronic active hepatitis.

(two) pathogenesis

The pathogenesis of mixed RTA should be similar to that of type I and II RTA.

1.H+ active transport causes lumen velocity to decrease

(1) Gradient defects: H+ transport is extremely sensitive to the inhibition of lumen H+ (cavity-cell or lumen-to-tubular H+ gradient), and its active transport velocity is reduced.

(2) H+ secretion deficiency: Even after the inhibition of H+ concentration is released, the transport of H+ from the cells to the lumen is still lower than normal, and the secretion ability is lowered.

2.H+ increases the rate of diffusion from the lumen to the cell (or to the stroma)

(1) Increased H+ reflux: The H+ permeability of the epithelial cell membrane or tight junction of the small tube increases, causing H+ to flow back from the lumen to the cell.

(2) Voltage-dependent H+ transport defects: The decrease in lumen Na+ or the increase in Cl-reabsorption reduces the negative charge of the lumen, reduces the secretion of H+ or increases the reflux of H+.

3. The ability to reabsorb HCO3- decreases

In normal people, HCO3-85% is reabsorbed in the proximal convoluted tubule, and when the acidification function of the proximal convoluted tubule is impaired, the ability to reabsorb HCO3- decreases, and excessive HCO3- is discharged from the urine. This hydrogencarbonate is lost. Reduces the amount of HC03- in the blood, forming acidosis and alkaline urine.

Mixed renal tubular acidosis prevention

For type III renal tubular acidosis, there is no effective preventive measures, and the prevention of secondary diseases should start with the treatment of basic diseases, control the development of renal tubular acidosis, and actively treat patients with disease to prevent the progress of the disease. The prognosis is good.

Mixed renal tubular acidosis complications Complications Metabolic acidosis hypokalemia vitamin D deficiency kidney stones uremia neurological deafness

Metabolic acidosis, hypokalemia, rickets, growth retardation, vitamin D deficiency or osteomalacia, partial renal calcification or renal calcification, advanced uremia, and a few neurological deafness.

Mixed symptoms of renal tubular acidosis Common symptoms Loss of appetite, nausea and vomiting, nausea, polyuria, renal calcification, dehydration, kidney area, dull pain, "duck step", gait bone pain

The typical clinical manifestations of mixed RTA are:

1. often have acidosis

Typical cases are hyperchloric acidemia, urine pH can be reduced to below 5.5, or there are diabetes, phosphorus, amino acid and urine.

2. Clinical manifestations of hypokalemia

Secondary aldosterone increase promotes K+ excretion, 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 low Potassium performance.

3. Urinary calculi.

4. Osteopathic

The incidence of bone disease is more common in patients with type I RTA. Children are characterized by vitamin D deficiency and osteopetrosis in adults.

5. Secondary hyperparathyroidism

In some patients, urinary phosphorus excretion decreased, and blood phosphorus decreased and secondary hyperparathyroidism occurred.

Mixed renal tubular acidosis test

Blood test

Mainly showed blood K+, Ca2, Na+, PO43-low, blood Cl- increased, plasma HCO3- decreased, CO2 binding decreased blood chlorine, blood HCO3- decreased, blood potassium normal or decreased.

2. Urine test

There is no cell component in the urine, HCO-excretion fraction is more than 5%, urine NH4+<500mmol/d, 24h urine Na+, K+, Ca2, PO43-excretion increases, urine pH>5.5, and urinary potassium excretion increases.

3. Load test

(1) Ammonium chloride test: common test for suspected and incomplete type I RTA; subject to ammonium chloride 0.1g / (kg · d), orally 3 times, for 3 consecutive days, 3 days per hour Leave urine for 1 time, measure urine pH and blood HCO3-, when blood HCO3- drops below 20mmol/L and urine pH>5.5, it has diagnostic value, and patients with liver disease switch to calcium chloride 1mmol/(kg·d). The determination with the positive result was the same as the ammonium chloride load test.

(2) Determination of urinary ammonium: The urinary ammonium excretion of normal people is about 40mmol/d, and the urinary ammonium excretion of type I RTA is <40mmol/d.

(3) Determination of urinary PCO2: 5% sodium bicarbonate intravenous infusion to maintain blood pH above 0.5h; when urine pH> blood pH, urine PCO2> blood PCO2 2.66kPa or more is diagnostic, that is, once The urine is alkaline, no matter whether the blood HCO3- concentration returns to normal, such as urine PCO2>9.3kPa, it can be considered that the H+ secretion ability of the collecting tube is not abnormal.

(4) urinary cystine test: cysteine urine often occurs in proximal convoluted tubule disease, if positive, it is helpful for diagnosis (cyanide nitrohydrocyanate test: take 5 ml of urine and 1 drop of concentrated ammonia, 5% 3 drops of sodium cyanide, positive for a purple-red reaction), and a subtype of type II RTA was diagnosed in an acid load test, such as urine pH < 5.5 or lower.

(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 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- is zero; Type II, mixed RTA > 15%, type I RTA < 3% to 5%.

2 Intravenous instillation of sodium bicarbonate method: 5% NaHC03 was added dropwise at a rate of 4 ml/min for 2 h. The blood pH, PCO2, HCO3-concentration and urine pH, HCO3-concentration were measured before injection; After 90 min, the blood pH was measured, PC02, HCO3-; 60, 120 min, urine pH and HCO3- were measured. When the patient's blood HCO3- returned to normal, the amount of HC03-excretion in the urine was 15% of the glomerular filtration excess, suggesting a proximal convoluted tubule. HCO3-absorption disorder, urinary HCO3-excretion fraction = (urine HCO3-/plasma HCO3-)/(urine creatinine/creatinine), plasma HCO3-concentration, type II RTA HCO3-excretion fraction >15%, type I RTA <5%, this method can identify type I, type II RTA.

4. Imaging examination

Fishmeal-like kidney stones can be found in KUB plain or IVP tablets, and bone disease can be known.

5. Ultrasound examination

Can understand whether the kidneys have calcification and stones.

Diagnosis and diagnosis of mixed renal tubular acidosis

Diagnostic criteria

Mixed renal tubular acidosis is similar to type I RTA. The diagnosis is based on the cause of type I RTA, high chloride acidosis, urinary ammonium >40mmol / d, ammonium chloride load test urine pH > 5.5, carbonic acid The sodium hydrogen load test, (UB) PCO2 < 4.0 kPa, can diagnose the disease.

Similar to type III RTA, type II RTA, the diagnosis is based on: high chloride acidosis, except for non-nephrogenic diseases, unexplained hypokalemia, hypophosphatemia, urine glucose positive, Increased urinary phosphorus, amino acid urine, urine pH>6.0; acid, alkali load test positive can diagnose the disease.

Differential diagnosis

The disease needs to be differentiated from type I, type II RTA and metabolic acidosis caused by glomerular diseases. The latter often has a decrease in glomerular filtration rate, and the clinical manifestations of azotemia also need to be associated with nitrogen retention. Other diseases of acidosis and other types of renal tubular acidosis, such as distal renal tubular acidosis may be confused with uremia acidosis, but metabolic acidosis of uremia has azotemia and elevated blood phosphorus Identification is not difficult.

Renal calcification caused by hereditary idiopathic hypercalciuria can cause distal renal tubular acidosis, and it needs to be differentiated from the primary one. The stone at this time can be calcium phosphate stone, but no low potassium. Hemorrhagic and metabolic acidosis, incomplete RTA, the most easily and idiopathic hypercalcemia can not be distinguished, at this time, can be used for ammonium chloride load test, secondary distal renal tubular disease caused by other diseases Acidosis has its own clinical characteristics.

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