This article explains renal tubular acidosis, including the symptoms, causes, and treatment.
Renal tubular acidosis is an acid-base disorder. It is a form of metabolic acidosis in which the pH of the blood drops below 7.35.
Normally, the body maintains a blood pH between 7.35–7.45. It does this by regulating three processes:
- buffering acids with different salts, electrolytes, and proteins in the blood
- excreting or reabsorbing bicarbonate, the main base, in the kidneys
- exhaling carbon dioxide, the main component of metabolic acids, from the lungs
Renal tubular acidosis occurs when there is a problem with the kidneys. Renal denotes the kidneys. Tubular refers to the renal tubules, which are part of the nephrons.
Nephrons are the basic unit of the kidney and number in the millions. They have a filter and a tubule. The filter cleans the blood and passes the filtered fluid to the tubule. The tubule reabsorbs any fluid, electrolytes, or nutrients the body still needs. The rest goes out of the kidneys as urine.
In renal tubular acidosis, the tubule either does not get rid of enough hydrogen ions or loses too much bicarbonate.
The concentration of hydrogen ions is what makes blood acidic. The higher the concentration, the more acidic the blood will be. Getting rid of hydrogen ions through the urine is one way to balance blood pH.
Bicarbonate is the main base in the blood. When the blood is acidic, it can latch on to the extra hydrogen ions and neutralize them.
There are three renal tubular acidosis types: type 1, type 2, and type 4. Type 3 is no longer part of the classification system, as it is likely a combination of 1 and 2.
Type 1 renal tubular acidosis
Type 1 is distal renal tubular acidosis. The distal, or far, end of the tubule is where hydrogen ion secretion takes place. In this form of renal tubular acidosis, the distal tubule does not get rid of enough hydrogen ions.
Type 2 renal tubular acidosis
Type 2 is proximal renal tubular acidosis. The proximal, or beginning, end of the tubule is where reabsorption of bicarbonate occurs. In type 2, the proximal tubule does not reabsorb enough bicarbonate.
Type 4 renal tubular acidosis
Type 4 starts with the hormone aldosterone. When aldosterone does not do its job, there is a disruption of potassium balance. The tubules allow too much potassium to remain in the blood, causing high levels of hyperkalemia. Hyperkalemia upsets acid secretion, causing acidosis.
This is the most common type of renal tubular acidosis.
In most cases, renal tubular acidosis does not cause symptoms. It is usually a mild and chronic form of acidosis.
When symptoms develop, they may include the following:
- abdominal pain
- appetite loss
- bone pain
- fatigue
- irregular heartbeat
- kidney stones
- muscle weakness
- paralysis
- slow or missing reflexes
- weight changes
Severe renal tubular acidosis can be life threatening.
The causes of renal tubular acidosis vary by type.
Type 1 renal tubular acidosis
There is an inherited form of renal tubular acidosis type 1. Other causes include:
- autoimmune diseases, such as Sjögren’s disease, lupus, and rheumatoid arthritis
- cirrhosis
- genetic conditions, such as sickle cell disease and Ehlers-Danlos syndrome
- high urine calcium
- kidney transplantation
- obstruction of the urinary tract
- medications, including certain antibiotics, antifungals, cancer chemotherapies, and lithium
Type 2 renal tubular acidosis
Type 2 renal tubular acidosis can also be an inherited disorder. Other causes include:
- Fanconi syndrome
- heavy metal poisoning, from lead or cadmium, for example
- inherited conditions, such as cystinosis, fructose intolerance, Lowe syndrome, and Wilson disease
- kidney transplantation
- multiple myeloma
- medications, including certain antibiotics, cancer chemotherapies, and acetazolamide
Type 4 renal tubular acidosis
This type involves aldosterone deficiency or inhibition from:
- Addison’s disease
- aldosterone synthase deficiency
- chronic interstitial nephritis
- critical illness
- diabetic nephropathy
- HIV nephropathy
- urinary obstruction
Medications that may cause type 4 renal tubular acidosis include:
- angiotensin-converting enzyme (ACE) inhibitors
- angiotensin II receptor blockers
- certain antibiotics, such as trimethoprim
- cyclosporine
- heparin
- nonsteroidal anti-inflammatory drugs (NSAIDs)
- potassium-sparing diuretics, such as spironolactone
It is generally not possible to prevent renal tubular acidosis.
To diagnose renal tubular acidosis, doctors will review your medical history and physical symptoms, if any. However, blood and urine tests are necessary to identify renal tubular acidosis and the type.
Standard tests include:
- arterial blood gases
- blood urea nitrogen
- creatinine
- electrolytes
Results will include:
- blood pH, which will be low in renal tubular acidosis, with a normal anion gap
- plasma bicarbonate, which will be low in renal tubular acidosis
- urine pH, which will be higher than it should be in renal tubular acidosis
- blood potassium, which will be high in type 4
Doctors may also order stimulation tests to determine which type of renal tubular acidosis you have. These tests involve giving you acid, base, or a diuretic. Your doctor then measures the results. For type 4, doctors may measure aldosterone and cortisol levels.
Treating renal tubular acidosis involves identifying and treating the underlying condition if possible. Otherwise, the main treatment is alkali therapy by drinking a basic solution of the following:
- potassium bicarbonate
- potassium citrate
- sodium bicarbonate
- sodium citrate
The choice depends on which type you have and whether you need potassium. Vitamin D supplements and diuretics may also be necessary.
Left untreated, complications can develop from type 1 and type 2 renal tubular acidosis, including:
- dental and bone disease, including rickets
- kidney stones and progressive kidney disease
- slowed growth in children
With type 4, high potassium levels can lead to heart problems, including cardiac arrest and death.
Here are some questions people often ask about renal tubular acidosis.
How serious is renal tubular acidosis?
Usually, renal tubular acidosis is a mild and chronic condition. However, it can lead to serious complications without treatment. This includes growth problems in children and progressive kidney disease in both adults and children. Type 4 can also cause fatal heart problems due to high potassium levels in the blood.
How do you reverse renal tubular acidosis?
Doctors reverse renal tubular acidosis with alkali therapy. This involves drinking a solution that is basic to counteract the acidosis. If possible, doctors will treat the underlying condition.
Renal tubular acidosis is a rare acid-base disturbance. It occurs due to problems in the kidneys’ ability to balance acid and base in the blood.
The most common type, type 4, also involves disruptions in the balance of potassium. Although this form of acidosis is often mild and chronic, it can cause serious complications.
