Renal tubular acidosis

Renal tubular acidosis is a condition characterized by acid pH in the body due to a defect in the kidney function.

Chemical balance is critical for our health. In a normal state, the acid-base balance of the human body ranges between a pH of 7.35 to 7.45. The most important chemicals in the body are sodium, chloride, potassium, calcium, ammonium, carbon dioxide, oxygen, and phosphates.

One of the most common ways to balance the pH of the body is through breathing. The carbon dioxide dissolved in the blood is an acid (carbonic acid). Faster breathing eliminates more carbon dioxide in the blood and increases the pH. Holding your breath does the opposite.

However, the kidneys also regulate acid-base balance somewhat more slowly than the lungs. Kidneys may filter, pass into to the blood or excrete into the urine different chemical to keep a proper acid-base balance. If the kidneys do not effectively remove acid from the body, it builds up in the blood, leading to a condition called metabolic acidosis.

When metabolic acidosis is caused by a failure of the kidneys is called renal tubular acidosis.

There are three main types of renal tubular acidosis:

• Distal renal tubular acidosis or type 1: Results from a failure in the normal urine acidification process. It may be hereditary or may be triggered by an autoimmune disease (lupus, Sjogren syndrome, rheumatoid arthritis), lithium therapy, kidney transplantation, or chronic obstruction.
• Proximal renal tubular acidosis or type 2: It is caused by a defect in bicarbonate reabsorption in the kidneys. It may be due to a hereditary disease (Fanconi's syndrome, fructose intolerance, Lowe's syndrome) or it may also be triggered by vitamin D deficiency, kidney transplantation, heavy metal poisoning, and treatment with certain drugs (acetazolamide, topiramate, sulfonamides, ifosfamide, tenofovir or streptozotocin).
• Type 4 renal tubular acidosis: It results from aldosterone deficiency or when the kidneys do not respond to aldosterone hormone in the renal tubules. It is associated with diabetes mellitus, sickle cell anemia, autoimmune diseases, or obstruction of the urinary tract.

* Type 3 renal tubular acidosis is very rare (a combination of type 1 and 2) and is no longer used. It is considered now a subtype of Type 1.

Symptoms may differ depending on the type of renal tubular acidosis:

• Distal renal tubular acidosis or type 1: There is a low level of potassium and high blood acidity. Symptoms may include dehydration, muscle weakness, paralysis (due to potassium deficiency), kidney stones (due to excess of calcium in the urine), polyuria (excessive production of urine), polydipsia (excessive or abnormal thirst) and osteomalacia (bones become soft and weak).
• Proximal renal tubular acidosis or type 2: It also results in high blood acidity and low blood potassium levels. The most common symptoms are dehydration, fatigue, muscle weakness and osteomalacia (bones become soft and weak).
• Type 4 renal tubular acidosis: In this case there is a high level of potassium in the blood and low blood acidity. It rarely causes symptoms unless potassium levels rise so high as to cause heart arrhythmias or muscle paralysis.

The treatment depends on the type of the renal tubular acidosis.

For type 1 and 2 the recommended treatment is the replacement of alkali (base). It requires to drink daily a solution of bicarbonate or sodium citrate to lower the acid level in the blood. It is usually needed also the intake of other chemicals that may be low such as potassium (using potassium citrate for example).

In Type 4 renal tubular acidosis it is necessary to reduce the level of potassium in the blood. This may be done by reducing the intake of potassium in the diet or by using diuretics (such as furosemide) that increase the potassium excretion in the urine.

When the balance of body chemicals is restored the prognosis is usually good.