Types of RTA

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.

source: http://kidney.niddk.nih.gov/kudiseases/pubs/tubularacidosis/index.htm