Renal Tubular Acidosis

Your 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. One researcher, pediatric neurologist Donald Lewis, has theorized that Charles Dickens may have been describing a child with RTA when he created the character of Tiny Tim in his famous story, "A Christmas Carol." Tiny Tim's small stature, malformed limbs, and periods of weakness are all possible consequences of the chemical imbalance caused by RTA. Among the evidence cited to support this theory is the fact that Tiny Tim's condition, while fatal in one scenario, is reversible when Scrooge pays for medical treatments, which in those times would likely have included sodium bicarbonate and sodium citrate, which are alkaline agents that would neutralize the acid in Tiny Tim's blood. Whether the literary diagnosis of Tiny Tim is correct or not, the good news is that medical treatment can indeed reverse the effects of RTA. To diagnose RTA, 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, RTA may be the reason, but additional information is needed first to rule out other causes. If RTA 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 RTA 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. At one time, doctors divided 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 today 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.