Types of RTA
Doctors used to divide RTA into four types.
- Type 1 is also called classic distal RTA. "Distal," which means
distant, refers to the point in the urine-forming tube where the defect
occurs. It is relatively distant from the point where fluid from the
blood enters the tiny tube (or tubule) that collects fluid and
wastes to form urine.
- Type 2 is called proximal RTA. The word "proximal," which means
near, indicates that the defect is closer to the point where fluid and
wastes from the blood enter the tubule.
- Type 3 is rarely used as a classification because it is now thought
to be a combination of type 1 and type 2.
- Type 4 RTA is caused by another defect in the distal tubule, but it
is different from classic distal RTA and proximal RTA because it results
in high levels of potassium in the blood instead of low levels. Either
low potassium (hypokalemia) or high potassium
(hyperkalemia) can be a problem because potassium is important in
regulating heart rate.
Type 1: Classic distal RTA
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 RTA
This form of RTA 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 RTA 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 RTA 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 RTA. 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 RTA
This form of RTA 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 RTA is distinguished
by a high blood-potassium level.
Low levels of aldosterone in the blood may be caused by drugs,
including
- A drug called spironolactone used to treat congestive heart
failure.
- A class of blood pressure drugs called angiotensin-converting enzyme
(ACE) inhibitors.
- An antibiotic called trimethoprim.
- An agent called heparin that keeps blood from clotting.
- An antibiotic called pentamidine used to treat pneumonia.
- A class of painkillers called nonsteroidal anti-inflammatory drugs
(NSAIDs).
- Immunosuppressants 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.
Keeping on Top of Your Condition
Keeping in tune with your disease or condition not only makes treatment less intimidating but also increases its chance of success, and has been shown to lower a patients risk of complications. As well, as an informed patient, you are better able to discuss your condition and treatment options with your physician.
A new service available to patients provides a convenient means of staying informed, and ensures that the information is both reliable and accurate. If you wish to find out more about HealthNewsflash's innovative service, take the tour.
| 
