Renal tubular acidosis overview

# Overview
Kidneys serve as a buffering system to maintain acid-base balance. Kidneys reabsorb the filtered bicarbonate and excrete acid to maintain acid-base balance. HCO3 reabsorption is facilitated by Na-H and proton pumps. Collecting tubules serve the function of excretion of acid. When ever there is disruption in the normal physiological mechanisms of tubular system of kidneys acidosis sets in. . Potassium is the most common electrolyte abnormality that can be noticed with renal tubular acidosis. It can be either hypokalemic renal tubular acidosis or hyperkalemic renal tubular acidosis. Renal tubular acidosis can be classified into type 1 (distal), type 2 (proximal), type 4 (hypoaldosteronism) and voltage-dependent RTA. Genetic mutations are the most common etiology for renal tubular acidosis. If left untreated renal tubular acidosis leads to growth failure and chronic kidney failure. Urine pH is the gold standard test for the diagnosis of renal tubular acidosis. Alkalization of the urine along with correction of electrolyte abnormalities is the mainstay of treatment in patients diagnosed by renal tubular acidosis. Sodium bicarbonate with potassium replacement are the medications recommended along with correction of underlying cause.

# Historical Perspective
Renal tubular acidosis was first described as separate entity by Dr. Lightwood in 1935. Later Dr.Butler in 1936 described the pathophysiology and genetic inheritance of renal tubular acidosis in the children.

# Classification
Based on underlying defect in concentration of urine process in renal tubule, renal tubular acidosis can be classified into type 1 (distal), type 2 (proximal), type 4 (hypoaldosteronism) and voltage-dependent RTA.

# Pathophysiology
Kidneys reabsorb the filtered bicarbonate and excrete acid to maintain acid-base balance. HCO3 reabsorption is facilitated by Na-H and proton pumps. Collecting tubules serve the function of excretion of acid. Renal tubular acidosis is described as any one of a number of disorders, in which either of above buffering mechanism is impaired. Potassium is the most common electrolyte abnormality that can be noticed with renal tubular acidosis. It can be either hypokalemic renal tubular acidosis or hyperkalemic renal tubular acidosis. Mode of inheritance can autosomal dominant or recessive depending upon type of disease abnormality, Common genes involved include ATP6V1B1, ATP6V0A4, SLC4A1.

# Causes
Primary causes of renal tubular acidosis include genetic mutations causing defects in the kidney anion exchanger  in distal tubule intercalated cells and congenital adrenal hyperplasia. Secondary causes include medications and autoimmune diseases.

# Differentiating Renal tubular acidosis from Other Diseases
Renal tubular acidosis must be differentiated form other diseases as most of them have a similar presentation of acidosis on ABG, dehydration (nausea and vomiting) and specific history pertaining to underlying etiology.

# Epidemiology and Demographics
The estimated annual incidence of distal renal tubular acidosis is 10 in 100,000 population. Renal tubular acidosis is more common in infants than other group of population. There is racial predilection for renal tubular acidosis.

# Risk Factors
Common risk factors in the development of renal tubular acidosis include childhoodurinary tract obstruction, diabetes mellitus, primary biliary cirrhosis, nephrocalcinosis, nephrolithiasis, Amphotericin-B therapy, cisplatinum, Untreated adrenal insufficiency.

# Screening
Screening for renal tubular acidosis is usually not recommended for asymptomatic patients. Screening is only recommended for patients with increased risk of having proximal RTA or metabolic disorders associated with the development of Fanconi syndrome.

# Natural History, Complications, and Prognosis
If left untreated renal tubular acidosis leads to growth failure and chronic kidney failure. Common complications associated with renal tubular acidosis include volume depletion, electrolyte disturbances, nephrocalcinosis, osteoporosis, growth retardation, renal rickets. Prognosis of renal tubular acidosis is generally good with appropriate therapy.

# Diagnosis

## Diagnostic Study of Choice
Urine pH is the gold standard test for the diagnosis of renal tubular acidosis.

## History and Symptoms
Patients with renal tubular acidosis can present with acute or chronic onset of symptoms. Patients usually doesn't have a typical history or symptoms. Common symptoms of renal tubular acidosis include vomiting, dehydration and electrolyte abnormalities with acidosis.

## Physical Examination
Patients with acute onset of renal tubular acidosis appear confused and stupor where as with chronic acidosis usually appear tired.

## Laboratory Findings
The diagnosis of renal tubular acidosis should be considered in any patient presenting with metabolic acidosis.The first step in diagnosing metabolic acidosis includes measuring the blood pH. The next steps includes measurement of urine pH and estimation of urinary ammonium excretion.

## Electrocardiogram
Electrocardiogram findings associated with renal tubular acidosis include changes due to potassium levels. Peaked T waves are the earliest sign of hyperkalemia. where as hypokalemia presents with ST segment depression, decreased T wave amplitude, and prominent U waves.

## X-ray
Electrocardiogram findings associated with renal tubular acidosis include changes due to potassium levels. Peaked T waves are the earliest sign of hyperkalemia. where as hypokalemia presents with ST segment depression, decreased T wave amplitude, and prominent U waves.

## Echocardiography and Ultrasound
There are no echocardiography/ultrasound findings associated with renal tubular acidosis.

## CT scan
There are no CT scan findings associated with renal tubular acidosis.

## MRI
There are no MRI findings associated with renal tubular acidosis.

## Other Imaging Findings
There are no specific imaging findings associated with renal tubular acidosis. However, imaging modalities can be helpful in diagnosing underlying complications of renal disease.

## Other Diagnostic Studies
There are no other diagnostic studies associated with renal tubular acidosis.

# Treatment

## Medical Therapy
Alkalization of the urine along with correction of electrolyte abnormalities is the mainstay of treatment in patients diagnosed by renal tubular acidosis. Sodium bicarbonate with potassium replacement are the medications recommended along with correction of underlying cause.

## Surgery
Surgical intervention is not recommended for the management of renal tubular acidosis.

## Primary Prevention
There are no effective primary preventive measures for renal tubular acidosis. However, preventive approaches can be helpful in the case of Fanconi syndrome secondary to toxin exposure which includes regulation of the use of medications responsible in high-risk groups with caution.

## Secondary Prevention
Secondary preventive measures of renal tubular acidosis are similar to primary prevention.