Primary Distal Renal Tubular Acidosis
Diagnosis and Testing
How do I get tested for primary distal renal tubular acidosis?
Testing for primary distal renal tubular acidosis (primary dRTA) often requires an examination by a doctor combined with a series of blood and urine tests. First, if a patient has symptoms of primary dRTA disease on exam, blood and urine tests will be done. Initial blood tests will look at the levels of electrolytes (such as potassium, sodium, and chloride), carbon dioxide (an acid), bicarbonate (a base), and pH. Initial urine tests will measure urinary electrolytes and pH levels. If testing finds a urine pH above 5.5, a normal blood anion gap, low serum potassium, and low blood pH levels it is suggestive of primary dRTA as possible diagnosis. Other early tests that may also help with diagnosis include the NH4Cl acidifying test and the furosemide test on blood. When doing these initial tests, it is important to collect the blood and urine samples before giving IV fluids (hydration therapy) as the extra fluid support it can interfere with test results and given false negatives.
If there are signs and symptoms of primary dRTA, the lab tests suggest primary dRTA, and other non-genetic causes of are ruled out, the doctor will often do a genetic blood test (called sequencing) looking at the "spelling" of the ATP6V1B1, ATP6V0A4, and/or SLC4A1 genes. The sequencing test looks for spelling changes in the code of the genes that cause them not to work correctly.
If a person has signs and symptoms of distal renal tubular acidosis (dRTA) and/or hearing loss, but has had a negative gene sequencing test, a genetic deletion/duplication test may be done next to look for missing or duplicated sections of the gene that would cause primary dRTA. Because of the methodology of a gene sequencing test, this missing or duplicated gene pieces can be overlooked during a standard sequencing genetic test.
A final testing option is a panel test for many genes at the same time. The panel test is run on blood, but tests for many genes that, when they have changes, are known to lead to distal renal tubular acidosis, kidney disease, or hearing loss.
For more information about genetic testing options, including panel testing, go to the Genetic Testing Registry.
A pediatric nephrologist (a pediatrician specializing in the kidney) can help with understanding more specifics about the disorder. A genetic counselor can help with ordering further diagnostic testing and determine which labs in the U.S. conduct testing for primary dRTA would be best if testing is appropriate. (Take a look at "Find a Genetic Counselor" in your area https://www.nsgc.org/findageneticcounselor).
Genetic Testing Registry[link Genetic Testing Registry Accessed 18NOV18
"Find a Genetic Counselor" https://www.nsgc.org/findageneticcounselor).
Merck manual- consumer version. Overview of Acid-Base Balance https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance Accessed 19NOV18.