Kidney function testing is a procedure to find out how well organ kidney work. Kidney examination also aims to: detect disorders of the organ.
Kidneys have various important roles for the body, one of which is filtering and removing metabolic waste substances from the blood. In addition, the kidneys are also responsible for regulating the balance of body fluids, regulating the production of red blood cells, and producing hormones that regulate blood pressure.
If damaged, the kidneys cannot perform these functions optimally, causing disturbances in the body. In these conditions, kidney function tests are needed to determine whether the disorder is from the kidneys.
Indications for Kidney Function Examination
Renal function tests are recommended for patients suspected of having impaired renal function. Symptoms that can indicate a person has impaired kidney function include:
- Nausea and vomiting with no clear cause
- Dry and itchy skin
- Tired easily
- Urinating more often or less often
- Difficult to urinate
- Pain when urinating
- Recurrent muscle cramps
- Swelling of the legs due to fluid buildup (edema)
- Uncontrolled high blood pressure
- Foamy urine
- Hematuria or bloody urine
- Hard to breathe
- Loss of consciousness
Kidney function tests are also performed on people who are at risk for impaired kidney function, namely people with the following conditions:
- Suffering from diabetes
- Have excess weight
- Suffering from hypertension
- Suffering from liver disease
- Have kidney structural abnormalities
- Suffering from heart and blood vessel disease
- Suffering from heart failure
- Have a family history of kidney disease
- Have a smoking habit
Types of Kidney Function Examination
Kidney function tests are performed by examining urine or blood samples. The following are some types of kidney tests:
Urinalysis
Urinalysis or urine test is done to detect protein and blood in the urine. The factors that are examined are the color and clarity of the urine, as well as the chemical content in the urine. Urinalysis also detects microscopic substances that may be in the urine, such as red blood cells, white blood cells, bacteria, and minerals.
24 hour urine test
A 24-hour urine test is done to measure the level of protein or creatinine that comes out of the urine for 24 hours. Creatinine is a waste product of muscle metabolism that should be excreted in the urine. Meanwhile, protein should not be obtained in large quantities in the urine.
Test albumin
The albumin test aims to detect the presence of albumin in the urine. Albumin is a protein in the blood that should not be in the urine. This test can be performed as part of a urinalysis or as a separate test (dipstick test).
Microalbumin test
Just like the albumin test, the microalbumin test also aims to detect albumin in the urine. This test is more sensitive than dipstick test, so it can detect albumin even in small amounts.
Urine albumin-to-creatinine ratio (UACR)
Urine albumin-to-creatinine ratio is a test that aims to compare albumin levels and creatinine levels in the urine. The UACR test is usually followed by a test glomerular filtration rate (GFR).
Bload urea nitrogen (BUN)test
Bload urea nitrogen (BUN) or urea level test aims to measure the level of urea in the blood. Urea is a waste product of protein metabolism that should be excreted through urine.
Serum creatinine level
Serum creatinine level aims to measure the level of creatinine in the blood. High creatinine levels in the blood can be a sign of kidney problems.
Creatinine clearance
Creatinine clearance This study aims to compare creatinine levels in 24-hour urine samples with creatinine levels in blood. That way, you can get an idea of how much metabolic waste is filtered by the kidneys every minute.
Glomerular filtration rate (GFR) test
Glomerular filtration rate (GFR) test is a blood test that aims to determine the ability of the kidneys to filter out metabolic waste. The GFR test can be used to determine the stage of kidney disease.
Kidney Function Check Warning
The results of kidney function tests can be influenced by several factors, such as health conditions or the consumption of certain drugs. Therefore, tell your doctor about your medical history and any medications, vitamins, or supplements you are currently taking.
Before Kidney Function Check
Preparation before undergoing a kidney function test depends on the type of test to be performed. Some of the common preparations that doctors recommend are:
- Avoid strenuous physical activity on the day of urine collection, as strenuous physical activity can increase the level of protein in the urine.
- Drink enough water on the day of the examination, which is about 8 glasses, so that the urine sample needed for the examination is sufficient.
- Fill in the form regarding personal data, such as age, height and weight, and gender, which are important for calculating eGFR.
Kidney Function Examination Procedure
Kidney function tests can be done by taking a urine sample or a blood sample. Further explanation is as follows:
Kidney function check with urine sample
In a kidney function test using a urine sample, the patient will be asked to perform the following steps:
- Clean the genitals with a cloth that has been provided by the clinic or hospital.
- Throw the urine that comes out at the beginning of urination into the toilet, then stop in the middle of urinating.
- Collect the urine that comes out next in a special container that has been prepared to fill of it.
- Close the urine sample container tightly.
It is important to remember, during the urine sampling process, the patient should not touch the inside of the container to avoid transferring bacteria from his hands to the urine sample.
For 24-hour urine sample collection, patients will be asked to collect urine samples in a special place every time they urinate for the next 24 hours. Usually, sample collection begins after the bladder is empty or after the first urination in the morning.
In infants and people who cannot perform the above process, the doctor will insert a catheter into the bladder through the urinary opening. After that, the urine that comes out will be accommodated in a container that has been prepared.
Kidney function tests with blood samples
In a kidney function test using a blood sample, the doctor will perform the following steps:
- Tie the patient's upper arm with a special rope, so that the patient's veins are clearly visible
- Clean the skin area around the veins using an antiseptic solution
- Insert a needle into a vein and draw a few milliliters of blood
- Remove the needle after enough blood has been drawn, then apply a plaster to the area where the needle was punctured to prevent bleeding
- Transferring blood into the sample tube
- Bring a blood sample to the laboratory for examination
After Kidney Function Check
A sample of the patient's urine or blood will be taken to a laboratory for further examination. At the next meeting, the doctor will tell you the results of the examination.
The following are the results of a kidney examination, based on the type of test performed:
Urinalysis results
Urinalysis results can be said to be abnormal if found sugar, protein, bacteria, white blood cells, or red blood cells in amounts that exceed the limit. In healthy kidneys, the amount of these substances is very little or even none at all.
However, the presence of these substances does not always indicate that a person has kidney disease. To get an accurate diagnosis, the doctor may perform further tests.
24 hour urine test results
The results of 24-hour urine collection were seen from the protein and creatinine content. The protein content in 24-hour urine should not be more than 100 mg/day. Meanwhile, the normal creatinine content in 24-hour urine depending on the gender of the patient, which is 955–2936 mg/day in men, and 601–1689 mg/day in women.
The presence of protein and creatinine that is outside normal limits can indicate the patient has the following conditions:
- Kidney stones
- Kidney infection
- Chronic kidney failure
- Glomerulonephritis
Albumin, microalbumin, and test results urine albumin-to-creatinine ratio (UACR)
The ratio of albumin to creatinine in urine (UACR) should not exceed 30 mg/g. For albumin content in the urine itself, the interpretation is as follows:
- 30–300 mg (microalbuminuria), indicating early stage kidney disease
- 300 mg (macroalbuminuria), indicates advanced kidney disease
test results creatinine clearance
test results creatinine clearance The normal range for men aged 19–75 years is 77–160 mL/min/BSA (milliliter per minute per body surface area). Meanwhile, normal test results in women depend on their age range. Here's the explanation:
- Age 18–29 years: 78–161 mL/min/BSA
- Age 30–39 years: 72–154 mL/min/BSA
- Age 40–49 years: 67–146 mL/min/BSA
- Age 50–59 years: 62–139 mL/min/BSA
- Age 60–72 years: 56–131 mL/min/BSA
Results lower than the range of values above can indicate decreased kidney function or impaired blood flow to the kidneys.
Blood creatinine test results
A normal test result in men aged 18–60 years is 0.9–1.3 mg/dL. Meanwhile, in women aged 18-60 years, a normal test result is 0.6-1.1 mg/dL. A result higher than this value can be caused by the following conditions:
- High protein diet
- Dehydration
- Urinary blockage
- Kidney infection or kidney damage
- Impaired blood flow to the kidneys, which can result from congestive heart failure, complications of diabetes, or shock
test results bload urea nitrogen (BUN)
The following are normal test results by age range:
- Children 1–17 years: 7–20 mg/dL
- Adult men: 8–24 mg/dL
- Adult women: 6–21 mg/dL
A BUN result higher than the above value may indicate kidney disease or kidney failure. However, it should be noted that the normal BUN test results for people aged 60 years and over will be slightly higher, when compared to the test results for people aged 60 years and under.
Resultstest glomerularfiltration rate(GFR)
GFR test results are divided based on the level of damage or interference with the kidneys. The details are as follows:
- 90: normal or with renal impairment without impaired renal function
- 60–89: renal impairment with mild renal impairment
- 45–59: mild to moderate impaired renal function
- 30–44: moderate to severe impaired renal function
- 15–29: severe renal dysfunction
- 15: kidney failure requiring dialysis or kidney transplant
In patients who get abnormal kidney function results, doctors may undergo additional tests to obtain a more accurate diagnosis.
Risks of Kidney Function Examination
Kidney function tests using a urine sample are generally safe and pose no risk, unless the sample is taken with a catheter. Use of a catheter, especially for a long time, can increase the risk of urinary tract or bladder infections.
While the kidney function tests using a blood sample, the risks that may occur include:
- Bleeding
- Pain, bruising, or infection at the site of the incision or needle puncture
- Hematoma (collection of blood under the skin)