Medical Terminology: Renal Function Tests

1. What are Renal Function Tests?
Metabolic waste is carried by the blood to the kidneys. The glomerulus in the kidneys acts as a filter to remove waste from the blood, which is collected in a tubule as urine. Metabolic waste such as sodium, potassium, and phosphorus can be reused by the body and are returned to the blood by the kidneys. The remaining waste is excreted as urine.
Renal function is measured in percentages. A person with two healthy kidneys has 100% renal function. Likewise, a person with one healthy kidney and one kidney in total renal failure is considered to have 50% renal function. A person will experience health problems if the person has 25% or less renal function. Dialysis is typically ordered for a patient with <15% renal function.
Renal failure occurs when the glomerulus no longer filters waste from the blood. This can occur suddenly (acute renal failure) in response to illness, medications, accidents, and poisons. It can also happen slowly (chronic kidney disease) from illnesses such as diabetes and high blood pressure. Chronic kidney disease can lead to end-stage renal disease when all or nearly all the renal function is permanently destroyed.

2. Blood Urea Nitrogen (BUN) Test
The blood urea nitrogen (BUN) test is used to screen for kidney function and dehydration and assess treatment for kidney disease and kidney dialysis.

Understanding the Blood Urea Nitrogen Test
Ammonia is formed when bacteria in the intestines break down protein. Ammonia is then converted into urea by the liver, which is excreted by the kidney in urine. Urea contains nitrogen. The BUN test measures the level of nitrogen in the blood derived from urea.
The BUN test is typically performed with the creatinine test. The health care provider uses the BUN: creatinine ratio to evaluate the patient’s condition.

3. Creatinine and Creatinine Clearance Test
The creatinine and creatinine clearance test is used to screen for kidney function and dehydration.

Understanding the Creatinine and Creatinine Clearance Test
Creatine phosphate provides energy to skeletal muscles. After 7. seconds of intense effort, creatine phosphate converts to creatine. Creatine is metabolized into creatinine and is carried in blood to the kidneys for filtering and is excreted in urine. If kidneys are malfunctioning, creatinine levels in the blood increase and creatinine levels in urine decrease. There are three types of creatinine tests:
. Blood Creatinine Level: This test measures the level of creatinine in blood.
. Creatinine Clearance: This test measures creatinine in a 24-hour urine sample and measures the level of creatinine in blood.
. Blood Urea Nitrogen: Creatinine Ratio (BUN:creatinine): This test compares the results of the blood urea test with the blood creatinine level test to assess for dehydration.
A normal blood creatinine level does not rule out kidney disease.
Urea is a by-product of protein metabolism in the liver that is excreted in urine. Fetal kidney function is assessed by testing the level of creatinine in amniotic fluid. The health care provider may order the glomerular filtration rate test to determine kidney function.

Basic Questions
Renal Function Tests

1. What is the function of the glomerulus?
The glomerulus in the kidneys acts as a filter to remove waste from the blood.

2. What happens to the waste from the blood?
Waste from the blood is collected in a tubule as urine. Metabolic waste such as sodium, potassium, and phosphorus can be reused by the body and are returned to the blood by the kidneys. The remaining waste is excreted as urine.

3. How is renal function measured?
Renal function is measured in percentages. A person with two healthy kidneys has 100% renal function. Likewise, a person with one healthy kidney and one kidney in total renal failure is said to have 50% renal function.

4. When is dialysis typically ordered?
Dialysis is typically ordered for a patient with <15% renal function.

5. When does renal failure occur?
Renal failure occurs when the glomerulus no longer filters waste from the blood.

6. What is acute renal failure?
Acute renal failure is the sudden failure of the glomerulus to filter waste from blood in response to illness, medication, accidents, or poisons.

7. What is chronic kidney disease?
Chronic kidney disease is the slow failure of the glomerulus to filter waste from blood in response to illness such as diabetes and high blood pressure.

8. What is end-stage renal disease?
End-stage renal disease is when all or nearly all the renal function is permanently destroyed.

9. What is the purpose of the blood urea nitrogen (BUN) test?
The BUN test is used to screen for kidney function and dehydration and assess treatment for kidney disease and kidney dialysis.

10. How does the BUN test work?
The blood urea nitrogen (BUN) test measures the level of nitrogen in the blood derived from urea.

11. How is ammonia formed?
Ammonia is formed when bacteria in the intestines break down protein.

12. What happens to ammonia in blood?
Ammonia is then converted into urea by the liver.

13. What would high-level BUN indicate?
High-level BUN would indicate that there is a high level of ammonia being converted into urea by the liver.

14. What is the purpose of the creatinine and creatinine clearance test?
The creatinine and creatinine clearance test is used to screen for kidney function and dehydration.

15. What is the purpose of creatine phosphate?
Creatine phosphate provides energy to skeletal muscles.

16. What is creatine?
After 7. seconds of intense effort of using skeletal muscles, creatine phosphate converts to creatine.

17. What is creatinine?
Creatine is metabolized into creatinine.

18. What happens to creatinine?
Creatinine is carried in blood to the kidneys for filtering and is excreted in urine.

19. What happens to creatinine if the kidneys malfunction?
If kidneys are malfunctioning, creatinine levels in the blood increase and creatinine levels in urine decrease.

20. What is the blood creatinine level test?
The blood creatinine level test measures the level of creatinine in blood.

21. What is the creatinine clearance test?
The creatinine clearance test measures creatinine in a 24-hour urine sample and measures the level of creatinine in blood.

22. What is the BUN:creatinine ratio?
The BUN:creatinine test compares the results of the blood urea test with the blood creatinine level test to assess for dehydration.

23. Does a normal blood creatinine level rule out kidney disease?
No. The level of creatinine may not have as yet reached abnormal levels.

24. How is fetal kidney function assessed?
Fetal kidney function is assessed by testing the level of creatinine in amniotic fluid.

25. What other test might the health care provider order to determine kidney function?
The health care provider might order the glomerular filtration rate test to determine kidney function.