Blood tests that show kidney function tests are Serum Creatinine Test, Blood Urea Nitrogen (BUN), Estimated Glomerular Filtration Rate (eGFR, and Cystatin C concentration.
What do kidneys do?
As we know our kidneys are the necessary organs of our body. The main function of the kidneys is to the filtration of the blood.
The kidney filters the waste materials out of the blood with the help of nephrons that are present in our kidney.
The waste that is filtered by our kidneys is thrown out of our body through urine.
What are the results of kidney function tests?
1) Plasma urea
- Urea is a waste that the body creates.
- A high level of urea indicates problems with kidneys.
2) Creatinine:
- Creatinine is the waste that generates in our bodies.
- Increased concentration in blood implies bad kidneys.
- Creatinine level is the indicators of our renal health
3) Electrolytes level:
- It includes the level of sodium, potassium, chlorides, bicarbonates
- These electrolyte levels provide the dehydration status of our bodies.
Why it is important to perform kidney function tests?
- Symptoms of kidney diseases may not be observed until as much as 30-40% of the kidney is damaged.
- Early detection of kidney dysfunction can help to minimize future damage.
- To diagnose the health status of kidney
- To diagnose renal diseases and to diagnose kidney failure.
- It checks dehydration status.
What are kidney function tests?
- Serum creatinine
- Blood Urea Nitrogen (BUN)
- Estimated Glomerular Filtration Rate (eGFR)
- 24-hour urine creatinine clearance test
- ACR (Albumin to Creatinine Ratio)
- Cystatin C
What blood test shows kidney function?
1. Serum Creatinine Test
Significance of creatinine
- Creatinine is the waste product of creatine. Our muscles use it to make energy.
- Creatinine moves in the blood to the kidneys and then our kidney excretes it.
- High levels in the blood might indicate that the kidneys are not working properly.
Normal values of serum creatinine
- 0.6 to 1.2 milligrams (mg) per deciliters (dl) in adult males and,
- 0.5 to 1.1 milligrams (mg) per deciliter (dl) in adult females.
2. Blood Urea Nitrogen (BUN)
Significance of BUN
- The liver produces ammonia (which contains nitrogen ) as a byproduct of protein metabolism.
- The nitrogen combines with elements such as hydrogen, carbon, and oxygen to form urea. This is also called urea nitrogen.
- Urea nitrogen is transported to the kidney from the liver by the bloodstream.
- Healthy kidneys remove urea nitrogen and other waste products from the blood through urine.
What is the normal value of BUN?
The normal value of BUN is 7 to 20 mg/dL or 2.5 to 7.1 mmol/L.
3. Estimated Glomerular Filtration Rate (eGFR)
What is eGFR?
- GFR is the short form of Glomerular Filtration Rate.
- It is the amount of blood that is filtered by the glomeruli per minute.
How Estimated Glomerular Filtration Rate (eGFR) is calculated?
From the different equations, the two most commonly used equations to calculate eGFR are as follows :
- Equation 1: Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation.
- Equation 2: Modification of Diet in Renal Disease Study (MDRD) equation
- Data required are a person’s blood creatinine level, cystatin C result, age, and assigned value based upon sex and race.
Interpretation of eGFR result
| Kidney Damage Stage
|
Description | Estimated GFR
|
| 1 | Normal or minimal damage with normal GFR | 90+ |
| 2 | Mild decrease in GFR | 60-89
|
| 3 | Moderate decrease in GFR | 30-59
|
| 4 | Severe decreased in GFR | 15-29
|
| 5 | Kidney failure | <15 |
4. Cystatin C concentration
- Cystatin C is a protein that is produced by cells in the body.
- If the level of cystatin C is too high in the blood than it may indicate that the kidneys are not working properly.
- It is also used in combination with serum creatinine for the calculation of eGFR.
- Serum Cystatin C is not affected by gender, age, race, and muscle mass.
The normal level of serum cystatin C
The normal level of serum cystatin C ranges from 0.6 to 1 mg/L.
What urine test detects kidney function?
1. 24-hour urine creatinine clearance test
Significance of 24-hour urine creatinine clearance test
- A creatinine urine test measures the amount of creatine in the urine.
- It is more accurate to collect the urine for a whole day to get the value of creatinine, rather than one sample of urine.
- The creatinine in urine can vary a lot based on diet, exercise, and hydration levels so, a single reading is not helpful.
The normal value of creatinine test
- 14 to 26 mg per kg of body mass per day for men.
- 11 to 20 mg per kg of body mass per day for women.
2. ACR (Albumin to Creatinine Ratio)
- Normal individuals excrete a very small amount of protein in the urine. Albumin is the most common type of protein in the urine.
- Albuminuria is increased excretion of urinary albumin and it is a sign of kidney damage.
How ACR is calculated?
The doctor calculates it by dividing albumin concentration in micrograms by creatinine concentration in milligrams from a urine sample.
The normal value of ACR
| ACR (microgram/mg)
|
Significance |
| Less than 30 | Normal to mildly increased
|
| 30-300 | Moderately increased
|
| More than 300 | Severely increased
|
Frequently Asked Questions (FAQs)
Can a blood test detect kidney problems?
Blood tests that show kidney function tests are Serum Creatinine Test, Blood Urea Nitrogen (BUN), Estimated Glomerular Filtration Rate (eGFR, and Cystatin C concentration.
What is normal creatinine?
The normal values of serum creatinine are 0.6 to 1.2 milligrams (mg) per deciliters (dl) in adult males and, 0.5 to 1.1 milligrams (mg) per deciliter (dl) in adult females.
The normal urine creatinine is 14 to 26 mg per kg of body mass per day for men and
11 to 20 mg per kg of body mass per day for women.
Is kidney function tested in CBC?
The kidney function tests include: Serum creatinine, Blood Urea Nitrogen (BUN), Estimated Glomerular Filtration Rate (eGFR), 24-hour urine creatinine clearance test, ACR (Albumin to Creatinine Ratio), and Cystatin C
Why kidney function test is done?
Symptoms of kidney diseases may not be observed until as much as 30-40% of the kidney is damaged.
Early detection of kidney dysfunction can help to minimize future damage.
To diagnose the health status of kidney
To diagnose renal diseases and to diagnose kidney failure.
It checks dehydration status.
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