Renal function testing measure how effectively your renal are functioning. The greater part of these tests check how well your kidneys clear waste from your framework. A renal function testing might include a blood test, 24-hour pee test or both. There are three forms of renal function testing, the first is to go to the hospital to test kidney function, the second is to collect blood through a blood collection kit sent from a nearby lab and then send it to the lab for testing, and the third is to test kidney function directly at home and get the results within 5 minutes.
What is renal function testing?
Renal function testing is urine or blood tests that evaluate how well your kidneys are working. Most of these tests measure glomerular filtration rate (GFR). GFR assesses how efficiently your kidneys clear waste from your system.
Renal Function Testings (RFT) are a group of tests that can be performed together to assess kidney (renal) function. These tests measure the levels of various substances in the blood, including several minerals, electrolytes, proteins and glucose (sugar), to determine the current health of the kidneys.
If the kidneys are not functioning properly, waste products can build up in the blood and body fluid levels may increase to dangerous amounts that can cause damage to the body or may be life-threatening. Many conditions and diseases can lead to kidney damage. The most common causes and major risk factors for kidney disease are diabetes and hypertension.
What do your renal function do?
Your kidneys are part of your urinary system. The two kidneys sit in the back of your abdomen just below your ribcage. They help your body filter waste materials and expel them as urine. Your kidneys are also vital for producing:
- Hormones that maintain blood pressure.
- Red blood cells, which carry oxygen throughout your body.
- Vitamin D, which maintains bone and muscle health.
Your kidneys remove wastes and extra fluid from your body. Your kidneys also remove acid that is produced by the cells of your body and maintain a healthy balance of water, salts, and minerals—such as sodium, calcium, phosphorus, and potassium—in your blood.
Without this balance, nerves, muscles, and other tissues in your body may not work normally.
Your kidneys also make hormones that help
- control your blood pressure
- make red blood cells
- keep your bones strong and healthy
Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.
Why might I need a renal function testing?
Some conditions, such ablood pressure, affect how well the kidneys work. If you have one of these conditions, your healthcare provider may use renal function testing to help monitor these conditions.
You may also need a renal function testing if you have symptoms that indicate possible kidney problems. These symptoms might include:
- Blood in your urine (hematuria).
- Painful urination (dysuria).
- Frequent urge to urinate.
- Problems with starting to pee.
What tests are done to check kidney function?
Your healthcare provider may order one or a few different types of renal function testings. You may have blood renal function testing, such as:
- Blood urea nitrogen (BUN) measures nitrogen (made from protein breakdown) in your blood.Urea nitrogen comes from the breakdown of protein in the foods you eat. A normal BUN level is between 7 and 20. As kidney function decreases, the BUN level rises.
- Estimated GFR (eGFR) calculates filtration rates based on your serum creatinine levels, age, gender, size and race.This test is a measure of how well the kidneys are removing wastes and excess fluid from the blood. It is calculated from the serum creatinine level using age and gender. Normal GFR can vary according to age (as you get older it can decrease). The normal value for GFR is 90 or above. A GFR below 60 is a sign that the kidneys are not working properly. Once the GFR decreases below 15, one is at high risk for needing treatment for kidney failure, such as dialysis or a kidney transplant.
- Serum creatinine looks for the buildup of creatinine, a waste product from muscle tissue breakdown.Creatinine is a waste product that comes from the normal wear and tear on muscles of the body. Creatinine levels in the blood can vary depending on age and body size. A creatinine level of greater than 1.2 for women and greater than 1.4 for men may be an early sign that the kidneys are not working properly. As kidney disease progresses, the level of creatinine in the blood rises.
24-hour urine tests including:
- Microalbuminuria looks for a specific protein called albumin.This is a more sensitive dipstick test which can detect a tiny amount of protein called albumin in the urine. People who have an increased risk of developing kidney disease, such as those with diabetes or high blood pressure, should have this test or an albumin-to-creatinine ratio if their standard dipstick test for proteinuria is negative.
- Urinalysis evaluates your urine for blood, proteins and function.Includes microscopic examination of a urine sample as well as a dipstick test. The dipstick is a chemically treated strip, which is dipped into a urine sample. The strip changes color in the presence of abnormalities such as excess amounts of protein, blood, pus, bacteria and sugar. A urinalysis can help to detect a variety of kidney and urinary tract disorders, including chronic kidney disease, diabetes, bladder infections and kidney stones.
What is eGFR in blood test?
Normal adults have eGFR values over 90. eGFR decreases with age, even in people without kidney disease. Please see the table below for average age-based estimates of eGFR.
Kidney function levels chart
| Age (years) | Average eGFR |
| 20–29 | 116 |
| 30–39 | 107 |
| 40–49 | 99 |
| 50–59 | 93 |
| 60–69 | 85 |
| 70+ | 75 |
What happens during a renal function testing urine testing?
You complete 24-hour urine renal function testing at home. For a 24-hour urine test, your provider will give you a container to collect urine. On the day of the test:
- Urinate into the toilet as usual after you first wake up.
- For the rest of the day, urinate into the container.
- On day two, urinate into the container when you first wake up.
- Complete the test by dropping your sample off at the healthcare provider’s office or laboratory.
What happens during a renal function testing in blood?
For renal function testing, you will need to provide a blood sample. You can collect a blood sample using a small needle and a test tube. The collected blood sample you can choose to send to the lab or use a home renal function testing.
A renal function blood testing usually measures the level of the waste product creatinine and certain dissolved salts (electrolytes) in your blood. The test is done to check for a number of aspects of kidney function.
- Creatinine is a waste product in your body that is made by your muscles. It passes into your bloodstream, and is usually passed out in your urine (pee). A high level of creatinine in your blood indicates that your kidneys may not be working properly.
- Dissolved salts that are routinely measured are sodium, potassium, chloride and bicarbonate. They are sometimes referred to as ‘electrolytes’. Abnormal blood levels of any of these may sometimes be due to a kidney problem.
- eGFR stands for estimated glomerular filtration rate. Although the level of creatinine in your blood is a useful guide to kidney function, the eGFR is a more accurate measure of how well your kidneys are filtering your blood. Using your blood creatinine, and your age and sex, your eGFR can be calculated by computer and reported with the creatinine blood test.
In some cases urea and uric acid are also tested which are other waste products.
- Urea is produced when protein is broken down by your body. Healthy kidneys get rid of more than 90% of the urea your body produces. A high level of urea in your blood may indicate that you are dehydrated, bleeding in your bowel, or that your kidneys may not be working properly.
- Uric acid is produced when purines are broken down. High uric acid is a risk factor for gout. This is usually measured when helping to diagnose gout and monitoring the response to treatment of gout.
What can I expect after a renal function testing?
Renal function testings are typically simple and cause no side effects. After blood renal function testing, some people experience:
- Bruising.
- Dizziness.
- Fatigue.
Blood tests and urine tests typically don’t cause long-term pain or complications. Call your healthcare provider if you have pain, fatigue, or other symptoms that don’t go away.
When should I know the results of a renal function testing?
How soon you receive renal function testing results can vary. Sometimes, your provider discusses the results of your renal function testing on the same day. Or your provider may send the test to a lab, and you receive results in a few days.
If you want to know how your kidney function is faster, or just a daily test, you can choose a renal function testing at home. This renal function testing does not take too long, and you can usually get the results within 5 minutes.
What is a normal renal function testing result?
The Urea Test uses a timed-endpoint method to measure the Urea (UR) concentrations in whole blood, serum, or plasma. The system monitors the change in absorbance at 620 nm at a fixed-time interval. The change in absorbance is directly proportional to the concentration of the metabolite in the specimen.
UR: Urea in the specimen is hydrolyzed to NH3 and CO2 by the action of urease, and an indicator layer containing an indicator that produces a detectable change by gaseous ammonia.
Reference values are listed in the chart below:
Urea (UR) 1.70~8.30mmol/L（10.21~49.85mg/dL）
Reference ranges may vary between laboratories. Every laboratory should establish its own reference range as needed. UR levels will have big physiological fluctuations depending on the food consumed or exercise.
The Creatinine Test uses a timed-endpoint method to measure the Creatinine (CR) concentrations in whole blood, serum, or plasma. The system monitors the change in absorbance at 620 nm at a fixed-time interval. The change in absorbance is directly proportional to the concentration of the metabolite in the specimen.
CR: Creatinine in the specimen is hydrolyzed to creatine by the action of creatininase. A sequence of three coupled enzymatic steps using creatinase, sarcosine oxidase, and peroxidase causes the oxidative coupling of 4-amino antipyrine to form a blue dye.
Reference values are listed in the chart below:
Men: 0.070~0.115mmol/L（0.79~1.30mg/dL）
Women:0.044~0.080mmol/L（0.50~0.90mg/dL）
Reference ranges may vary between laboratories. Every laboratory should establish its reference range as needed. CR levels will have big physiological fluctuations depending on the food consumed or exercise.
What if my renal function testing results show early kidney disease?
If the renal function testing shows irregular results, you can follow up with your doctor about treatment options. You may receive medications to control your blood pressure. Or you may follow up with a nephrologist (a doctor who specializes in the kidneys).
If your renal function testing results are not typical, your doctor may order more frequent renal function testing. Regular testing can help your provider keep track of your health and any potential conditions.
Renal function testing check how well your kidneys are working. Healthy kidneys help remove waste from your body. Conditions such as diabetes or high blood pressure can affect your kidney function.
You may also need renal function testing to diagnose or rule out infections. Renal function testing include a blood test or urine test. Usually, your provider will give you the results on the same day or within a few days.
1. Kidney Function Tests: Types, Results & Follow Up
See also:
2. 2022 Best At-Home Kidney Test Buyers Guide
3. Chronic Kidney Disease: Causes, Symptoms And Management
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