What is Renal Tubular Acidosis (RTA)

Renal Tubular Acidosis (RTA) is a disease of the kidneys – Namely the renal tubules.

There are three main types of renal tubular acidosis – Type one, type two, and type four. Type three renal tubular acidosis is a term no longer used for its defining feature resolved with age and was not part of the pathological process. The type of RTA is assigned depending on which part of the acid handling mechanism is affected.

Statistics on Renal Tubular Acidosis (RTA)

There are no widely accepted statistics on the rate of RTA. The disease, however, does occur at any age and afflicts men more so than women.

Risk Factors for Renal Tubular Acidosis (RTA)

Type 1 – This condition may be inherited or acquired. In the majority of cases, this form of RTA results from the presence of another disease such as Sjogren’s syndrome, hypergammaglobulinaemia, chronic active hepatitis and systemic Lupus Erythematosus.

Type 2 – This condition may also be inherited or acquired. The pattern of inheritance in this condition is more unpredicyable than that of type 1 RTA. This condition may also be present in associated with other disease states such as Fanconi Syndrome and can be induced by certain drugs such as acetazolamide.

Type 4 – This condition cannot be inherited and is exclusively acquired. It occurs in patients with poor kidney function and may arise or be made worse with the use of drugs such as trimethoprim, anti-inflammatory drugs, ACE inhibitors and heparin.

Progression of Renal Tubular Acidosis (RTA)

Type 1 RTA
This condition causes prolonged blood acidity increasing the breakdown of calcium within the bony skeleton of the body. This increases the concentration of calcium within the bloodstream. More calcium is therefore allowed to enter the kidneys.

In the presence of blood acidity, the kidneys are unable to re-absorb calcium from the urine, and allows urine to pass to the bladder with a high concentration of calcium. This calcium may precipitate and form crystals and stones within the kidneys themselves and within the urinary tract. Because of increases bone turnover and poor production of vitamin D in the affected kidneys, rickets may occur in children and osteomalacia within adults.

Type 2 RTA
This primary problem in this form of RTA is that the kidneys cannot re-absorbe bicrabonate, which is lost in great amounts through the urine. The blood therefore becomes more acidic, resulting in incresaed bone turnover as occurs in type one, and increased urinary excretion of calcium. Renal stones are far less common in type 2 RTA, however, due to the presence of normal concentrations of urinary citrate, which prevents the formation of calcium urinary stones.

Type 4 RTA
The main problem in type 4 RTA is the inadequate production or response to the hormone aldosterone. This may result from poor aldosterone production or from poor kidney response to aldosterone due to kidney damage. The main concern in this condition is increased blood potassium levels which can rarely induce irregular heart beats which may be fatal. High blood potassium must be treated as a high priority in these patients. Type 4 RTA rarely suffers the complication of urinary stones.

How is Renal Tubular Acidosis (RTA) Diagnosed?

Blood tests will be required to assess kidney function and the severity of blood acidity. Urine samples will also be taken to determine the type of renal tubular acidosis so as to guide further management.

Prognosis of Renal Tubular Acidosis (RTA)

The disorder must be treated to reduce its effects and complications, which can be permanent and/or life-threatening. Most cases resolve successfully with treatment.

How is Renal Tubular Acidosis (RTA) Treated?

For types 1 and 2 RTA, treatment mainly consists of neutralising the acidity of the blood with alkali agents with agents such as sodium bicarbonate. Potassium tablets may also be required if the potassium concentration of the plasma is low.

Type 4 RTA requires primary treatment of the high potassium concentration present within the blood. Once treated, the acidity of the blood will usually resolve spontaneously, as it interacts with a lower blood potassium level.

Patients should be started on a low potassium diet as prescribed by their doctor and certain drugs may need to be stopped. Diuretic medications may also be required in the long term to prevent future escalation of potassium levels.

Renal Tubular Acidosis (RTA) References

[1] Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
[2] Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
[3] Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 545-549.
[4] Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001
[5] Penney MD., Oleesky DA. Renal Tubular Acidosis. Ann Clin Biochem 1999; 36:408-422.