Proximal renal tubular acidosis

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at December 30, 2016
StartDiseasesProximal renal tubular acidosis

Proximal renal tubular acidosis (proximal RTA) is a condition in which the patient's kidneys are unable to properly reabsorb bicarbonates. If left untreated, this causes a buildup of acid in the body which will begin to harm the patient in many ways, most notably in the skeletal system. Proximal RTA, which is also known as RTA Type II is strongly associated with Fanconi syndrome and other conditions in which metabolic functioning is impaired.

Contents

Definition & Facts

Proximal renal tubular acidosis is a type of renal tubular acidosis. Renal tubular acidosis is a condition in which the blood and tissues of the body are much more acidic than usual. In the case of proximal renal tubular acidosis, this increased acidity is a result of the kidneys being unable to absorb bicarbonate.

Bicarbonate is an alkaline substance that aids in reducing the acidity of bodily fluids. The kidneys ordinarily reabsorb this bicarbonate so that it can be reused in the body. For this purpose they use the proximal tubular cells, which are contained in the nephrons, the primary units that make up the kidney.

When these cells are unable to reabsorb bicarbonate, this causes a shortage of bicarbonate in the body. This directly leads to an increase in the body's acidity, which then results in a host of undesirable conditions in the patient.

Symptoms & Complaints

The buildup of acid in the body causes a variety of symptoms known as metabolic acidosis. Sometimes it is the nervous system that is affected, in which case the patient may experience fatigue, weakness, confusion, and a general reduction in alertness. Without treatment, it is possible for the patient's brain to become so impaired that the patient falls into a coma.

Other symptoms may include cramps in the muscle and changes in the heartbeat, especially an irregular heartbeat. There is also a tendency towards a lessening in urine volume and frequency, and pain may occur throughout the patient's body.

Especially in the case of a patient with Fanconi syndrome, there may be damage and weakening of the skeletal structure. Without prompt treatment, this may contribute to the development of diseases such as rickets and osteomalacia, a condition in which the bones are softened. Children with Fanconi syndrome and/or proximal RTA may experience less growth than expected and a reduced ability to absorb vitamin D.

Causes

Proximal renal tubular acidosis may be caused by many different inherited or acquired syndromes. One of the more commonly associated syndromes is Fanconi syndrome, in which the proximal tubular cells of the kidneys' nephron structures release substances into the urine that they would normally retain for later use by the body. Fanconi syndrome is often due to a genetic abnormality, but can also occur later in life when the kidneys are damaged.

There are a few other disorders that can also cause proximal RTA. One of these is Wilson's disease, a genetic disorder in which the body accumulates copper, and another is cystinosis, in which the body accumulates cystine. There is also multiple myeloma, a blood cancer that can impair kidney function, and Lowe syndrome, an X-linked recessive disease that primarily affects men.

Many metabolic syndromes, such as tyrosinemia (inability to metabolize tyrosine), galactosemia (inability to metabolize galactose), and hereditary fructose intolerance can prompt the occurrence of proximal RTA.

Certain chemotherapy drugs such as ifosfamide and antibiotics such as expired tetracycline, and even acetazolamide, which is a medication for treating glaucoma and epilepsy, might also cause proximal RTA in a patient.

Diagnosis & Tests

Testing for proximal renal tubular acidosis can be done by checking the pH level of the blood and the urine by various methods, such as a blood gas test in which the levels of oxygen and carbon dioxide in the blood is measured. The physician may also perform an acid loading test to verify whether the kidneys can effectively control the acid-base balance of the body. 

Additionally, the composition of the blood or urine may be analyzed by means of a metabolic panel or a urinalysis, respectively. The levels of various compounds will alert the physician to any problems with the functioning of the kidneys.

Treatment & Therapy

Treatment of proximal renal tubular acidosis consists of methods to reduce the acidity of the body and increase the amount of electrolytes to normal levels. By this method, most or all of the symptoms of proximal RTA may be addressed.

Akali therapy is a common way to address the reduction of bicarbonate in the body. Bicarbonate supplements can be given to the patient in sufficient amounts to negate its loss by way of the patient's urine. If needed, supplements of citrate, a metabolic equivalent to bicarbonate, may be substituted instead. 

Because the amount required for the supplement can be very large, thiazide diuretics can be administered to reduce this amount. Potassium should be taken alongside these diuretics as the treatment can exacerbate the leaching of potassium from the body.

Harm to the skeletal system as a result of proximal RTA can be counteracted with vitamin D supplements and calcium supplements, especially for children suffering from proximal RTA.

Treatment may sometimes not be necessary in the case of adults with proximal RTA. In general, treatment for children is mandatory due to the impairment in the growth and development of the skeletal system that is typical for this disease.

Prevention & Prophylaxis

Proximal renal tubular acidosis is often not preventable. It is usually caused by genetic disorders and therefore the only way to address it is through prompt and frequent treatment of the increased acidity of the body in an effort to counteract the symptoms.

For those cases of proximal RTA caused by acquired means, treatment is a matter of removing the cause. In the case of multiple myeloma, successful treatment of the cancer can cure proximal RTA. If the cause is a medication, then a physician will most likely recommend adoption of an alternative drug in its place.