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Renal Tubular Acidosis

Our body's cells use chemical reactions to carry out tasks such as turning food into
energy and repairing tissue. These chemical reactions generate acids. But too
much acid in the blood—acidosis—can disturb many bodily functions. Healthy
kidneys help maintain acid-base balance by excreting acids into the urine and
returning bicarbonate—an alkaline, or base, substance—to the blood. This
"reclaimed" bicarbonate neutralizes much of the acid that is created when food is
broken down in the body.

Renal tubular acidosis (RTA) is a disease that occurs when the kidneys fail to
excrete acids into the urine, which causes a person's blood to remain too acidic.
Without proper treatment, chronic acidity of the blood leads to growth
retardation, kidney stones, bone disease, and progressive renal failure.

Diagnosis

To diagnose renal tubular acidosis, your doctor will check the acid-base balance in
samples of your blood and urine. If the blood is more acidic than it should be and
the urine less acidic than it should be, renal tubular acidosis may be the reason,
but additional information is needed first to rule out other causes. If renal tubular
acidosis is suspected, additional information about the sodium, potassium, and
chloride levels in the urine and the potassium level in the blood will help identify
which of the three types of renal tubular acidosis you have. In all cases, the first
goal of therapy is to neutralize acid in the blood, but different treatments may be
needed to address the different underlying causes of acidosis.

Types of Renal Tubular Acidosis

Type 1: Classic Distal Renal Tubular Acidosis
This disorder may be inherited as a primary disorder or may be one symptom of a
disease that affects many parts of the body. Researchers have now discovered
the abnormal gene responsible for the inherited form. More often, however,
classic distal RTA is a complication of diseases that affect many organ systems
(systemic diseases), like the autoimmune disorders Sjögren's syndrome and lupus.

Other diseases and conditions associated with distal RTA include
hyperparathyroidism, a hereditary form of deafness, analgesic nephropathy,
rejection of a transplanted kidney, renal medullary cystic disease, obstructive
uropathy, and chronic urinary tract infections.

A major consequence of classic distal RTA is low blood-potassium. The level drops
if the kidneys excrete potassium into urine instead of returning it to the blood
supply. Since potassium helps regulate nerve and muscle health and heart rate,
low levels can cause extreme weakness, cardiac arrhythmias, paralysis, and even
death.

Untreated distal RTA causes growth retardation in children and progressive renal
and bone disease in adults. Restoring normal growth and preventing kidney
stones, another common problem in this disorder, are the major goals of therapy.
If acidosis is corrected with sodium bicarbonate or sodium citrate, then low blood-
potassium, salt depletion, and calcium leakage into urine will be corrected. Alkali
therapy also helps decrease the development of kidney stones. Potassium
supplements are rarely needed except in infants, since alkali therapy prevents the
kidney from excreting potassium into the urine.

Type 2: Proximal Renal Tubular Acidosis
This form of renal tubular acidosis occurs most frequently in children as part of a
disorder called Fanconi's syndrome. The symptoms of Fanconi's syndrome include
high levels of glucose, amino acids, citrate, and phosphate in the urine, as well as
vitamin D deficiency and low blood-potassium.

Proximal renal tubular acidosis can also result from inherited disorders that disrupt
the body's normal breakdown and use of nutrients. Examples include the rare
disease cystinosis (in which cystine crystals are deposited in bones and other
tissues), hereditary fructose intolerance, and Wilson's disease.

Proximal renal tubular acidosis also occurs in patients treated with ifosfamide, a
drug used in chemotherapy. A few older drugs—such as acetazolamide or
outdated tetracycline—can also cause proximal RTA. In adults, proximal RTA may
complicate diseases like multiple myeloma, or it may occur in people who
experience chronic rejection of a transplanted kidney.

When possible, identifying and correcting the underlying causes are important
steps in treating the acquired forms of proximal renal tubular acidosis. The
diagnosis is based on the chemical analysis of blood and urine samples. Children
with this disorder would likely receive large doses of oral alkali, such as sodium
bicarbonate or potassium citrate, to treat acidosis and prevent bone disorders,
kidney stones, and growth failure. Correcting acidosis and low potassium levels
restores normal growth patterns, allowing bone to mature while preventing
further renal disease. Vitamin D supplements may also be needed to help prevent
bone problems.

Type 4: Hyperkalemic Renal Tubular Acidosis
This form of renal tubular acidosis is most often referred to as type 4. It occurs
when blood levels of the hormone aldosterone are low or when the kidneys do
not respond to it. Aldosterone directs the kidneys to regulate the levels of sodium,
potassium, and chloride in the blood. Type 4 renal tubular acidosis is distinguished
by a high blood-potassium level.

Hyperkalemic distal renal tubular acidosis may result from sickle cell disease,
urinary tract obstruction, lupus, amyloidosis, or transplantation.

Aldosterone's action may be impeded by drugs, including

diuretics used to treat congestive heart failure such as spironolactone or
eplerenone

blood pressure drugs called angiotensin-converting enzyme (ACE) inhibitors and
angiotensin receptor blockers (ARBs)

the antibiotic trimethoprim

an agent called heparin that keeps blood from clotting

the antibiotic pentamidine, which is used used to treat pneumonia

nonsteroidal anti-inflammatory drugs (NSAIDs)

some immunosuppressive drugs used to prevent transplant rejection

For people who produce aldosterone but cannot use it, researchers have now
identified the genetic basis for their body's resistance to the hormone. To treat
type 4 RTA successfully, patients may require alkaline agents to correct acidosis as
well as medication to lower the potassium in their blood.

If treated early, most people with RTA will not develop permanent kidney failure.
Therefore, the goal is early recognition and adequate therapy, which will need to
be maintained and monitored throughout the patient's lifetime.

Content Source NIDDK.NIH

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