Section 11. Kidney and Urinary Tract Disorders

Chapter 146. Tubular and Cystic Kidney Disorders

Topics: Introduction | Renal Tubular Acidosis | Renal Glucosuria | Nephrogenic Diabetes Insipidus | Cystinuria | Fanconi's Syndrome | Hypophosphatemic Rickets | Hartnup Disease | Bartter's Syndrome | Liddle's Syndrome | Polycystic Kidney Disease | Medullary Cystic Disease | Medullary Sponge Kidney | Alport's Syndrome | Nail-Patella Syndrome

Renal Tubular Acidosis

In renal tubular acidosis, the kidney tubules cannot adequately remove acids from the blood to excrete them in the urine.

Normally, the breakdown of food produces acids that circulate in the blood. The kidneys remove acids from the blood and excrete them in the urine. This function is predominantly performed by the kidney tubules. In renal tubular acidosis, one of several causes of metabolic acidosis, the ability of the kidneys to excrete acids is partially impaired, and acid levels build up in the blood. The balance of electrolytes is also affected. Renal tubular acidosis may lead to the following problems:

• Low or high potassium levels in the blood
• Calcium deposits in the kidneys
• Dehydration
• Painful softening and bending of the bones (osteomalacia or rickets)

Renal tubular acidosis may be hereditary or may be caused by drugs, such as acetazolamide and amphotericin B; poisoning by some heavy metals; or an autoimmune disease, such as systemic lupus erythematosus or Sjögren's syndrome.

Symptoms and Diagnosis

Three types of renal tubular acidosis exist: type 1, type 2, and type 4. Each type produces slightly different symptoms. When potassium levels in the blood are low, as occurs in types 1 and 2, neurologic problems may develop, including muscle weakness, diminished reflexes, and even paralysis. In type 4, potassium levels typically increase, although it is uncommon for the level to rise high enough to cause symptoms. If the level becomes too high, irregular heartbeats and muscle paralysis may develop. In type 1, kidney stones may develop, causing damage to kidney cells and, in some cases, chronic kidney failure.

A doctor considers the diagnosis of type 1 or type 2 renal tubular acidosis when a person has certain characteristic symptoms (muscle weakness, diminished reflexes) and when tests reveal high levels of acid and low levels of bicarbonate and potassium in the blood. Type 4 renal tubular acidosis is usually suspected when high potassium levels accompany high acid levels and low bicarbonate levels in the blood. Special tests help to determine the type of renal tubular acidosis.

See the table Types of Renal Tubular Acidosis.

Treatment

Treatment depends on the type. Types 1 and 2 are treated by drinking a solution of sodium bicarbonate (baking soda) every day to neutralize the acid that is produced from food. This treatment relieves the symptoms and prevents kidney failure and bone disease or keeps these problems from becoming worse. Other specially prepared solutions are available, and potassium supplements may also be required. In type 4, the acidosis is so mild that bicarbonate may not be needed. High potassium levels in the blood can usually be kept in check by restricting the potassium intake and, if necessary, taking diuretics.