The word 'renal' refers to the kidney, both words interchangeable. A renal function test is a series of tests done to ascertain whether the kidneys are functioning properly.
The kidneys are two bean-shaped organs on either side of the spine at your back and their primary function is filtration. They rid the body of waste products of metabolism, maintain balance of electrolytes (Calcium, sodium, potassium) and they also keep acid-base levels balanced.
There are several tests carried out based on each function of the kidneys. The tests are classified into;
- Glomerular filtration tests
- Tubular function test
- Renal blood flow test
- Others
Based on Glomerular filtration, there is the clearance test. A clearance test measures the rate of excretion of a given substance by the kidneys.
There are three types of clearance tests;
- Urea clearance test
- Inulin clearance test
- Creatinine clearance test
For the purpose of this post, I'll run through Urea clearance test only.
Urea clearance is the volume of blood that can be completely cleared of urea per minute by the kidney. The normal Urea clearance range is 75 ± 10. In a case where the clearance level is high, it indicates there is a problem with the kidneys.
The test is preferably done in the morning between breakfast and lunch. The patient is expected to be at rest, have a light meal and drink about 3 glasses of water. The bladder is then emptied and urine discarded. An hour later, urine is collected and also blood sample collected for testing. The average value of both specimens is used to determine the urea content.
70% or more indicates the kidneys are excreting properly.
A 40% to 70% value is indicative of a mild impairment of renal function.
20% to 40% is indicative of a moderate impairment of renal function.
20% is indicative of severe impairmentofrenalfunction.
I hope this is simplified enough and you're not completely clueless when next you go for a laboratory check.