Chronic Kidney Disease Lab Tests
Regular testing is crucial in addressing chronic kidney disease (CKD) at an early stage. Immediate diagnosis and treatment can help preserve your kidney functions, keep them working for the long term, and delay dialysis.
Your doctor will require your full participation in managing your CKD. This is why it is important that you understand the purpose of these tests and what your results reveal about your condition.
Vital Tests That Help Diagnose CKD
Properly functioning kidneys clean up wastes and remove extra fluids from the blood. Conducting blood and urine tests help gauge how well your kidneys are filtering out wastes from your body.
Below are the common chronic kidney disease lab tests performed to assess kidney function (Note: Results from these tests may vary from one laboratory to another. Make sure to learn the standard values for your lab).
1. Estimated Glomerular Filtration Rate (eGFR) - This test measures the rate of blood flow through the kidneys. You may look at this number as the percentage of your kidney function. eGFR is also used to identify which stage of CKD you may be in.
Below are the eGFR values based on every CKD stage:
60 to 89
45 to 59
30 to 44
15 to 29
The eGFR is calculated from the serum creatinine level in your blood (which is influenced by factors like age, gender, height, weight, and race).
Standard eGFR can differ based on age. It decreases as people get older, even in people without kidney disease. The normal eGFR number for adults is 90 or higher. The chart below shows the average eGFR numbers per age range according to the National Kidney Foundation:
20 to 29
30 to 39
40 to 49
50 to 59
60 to 69
A filtration rate of 60 and below indicates that the kidneys are not working well. If a person’s eGFR approaches 15 and lower, he must start looking for renal replacement therapy (RRT) to replace the blood-filtering function of his kidneys. Treatments under RRT include kidney transplant and dialysis (hemodialysis or peritoneal dialysis).
2. Serum Creatinine - Creatinine is the waste material produced during the wear and tear of the muscles. Healthy kidneys remove it from the blood and dispose of it through the urine. The serum creatinine test is performed to measure the amount of creatinine in your blood.
People with impaired kidneys are prone to creatinine buildup in their blood. And as kidney functions continue to decline over time, serum creatinine levels increase. Generally, a creatinine level greater than 1.4 in men and greater than 1.2 in women may be a possible indication of kidney problems.
3. Blood Urea Nitrogen (BUN) - Urea nitrogen is a natural waste product that is generated after the body breaks down protein from the foods you eat. Your kidneys remove urea nitrogen from your blood. But when the kidneys are not functioning properly, this waste product stocks up in your blood, leading to an increase in BUN levels. A normal BUN value should be within 7 to 20 mg/dL. Your protein intake can also shoot up or lower your BUN.
4. Hemoglobin - This is the component in the red blood cells that delivers oxygen from the lungs to different parts of the body. Your doctor measures your hemoglobin levels to check if you have anemia, which can cause you to feel tired and sluggish.
Most people with kidney disease develop anemia during the early stage of CKD. Anemia may worsen as kidney disease progresses and when the kidneys can no longer produce the hormone erythropoietin (EPO, vital in red blood cell production).
5. Hematocrit - Your doctor also measures your hematocrit or the ratio of red blood cells to your total blood volume. For instance, a hematocrit of 42% means there are 42mL of red blood cells in 100mL of blood.
A low hematocrit can indicate that you have anemia. Normal hematocrit ranges depend on age and gender.
6. Parathyroid Hormone (PTH) - Increased PTH can lead to a poor balance of calcium and phosphorus. This can result in bone disease. It’s important that you ask your doctor if your PTH level is in the healthy range. Your doctor may prescribe a vitamin D supplement to reduce your PTH. Do not take over-the-counter vitamin D without your doctor’s advice.
7. Total Cholesterol - High cholesterol levels can put you at risk of heart problems. In most patients, a total cholesterol of 200 or lower is ideal. If your cholesterol level exceeds 200, you may need to adjust your exercise and diet.
All of us have protein in our blood. The primary protein present in the blood is called albumin. As part of its filtration process, healthy kidneys remove unnecessary fluid and waste from the blood, then release protein and essential nutrients into the bloodstream.
Impaired kidneys can leak out certain amounts of albumin into the urine. The presence of excess protein in the urine is called proteinuria (happens when a damaged kidney excretes 150 mg of protein to the blood daily). This condition hints at a possible kidney disorder or an indicator of early-stage CKD.
To determine if you have protein in your urine and to assess its relation to your kidney function, you need to have a urine test.
You may be required to give a sample of your urine or collect all the urine you produced over the past 24 hours. The 24-hour urine test aims to see how well your kidneys are functioning and measure the amount of protein your kidneys excrete to your urine in a day.
Below are the types of urine tests:
1. Urinalysis - Evaluates the appearance, content, and concentration levels of urine. A urinalysis helps in the early detection and management of various health conditions including kidney disease, bladder infections, urinary tract infections, kidney stones, and diabetes.
Your urine can be evaluated through a visual exam, dipstick test, or microscopic exam. A dipstick test uses a chemically treated plastic strip placed into the urine to detect abnormalities. The strip changes color if there are certain substances present or if their levels are beyond normal.
A dipstick test is commonly performed to check for:
- Protein content
- Signs of infection
In a microscopic exam, drops of your urine sample are viewed under a microscope to see if there are abnormal levels of the following:
- Red blood cells - Possible sign of kidney disease
- White blood cells - May be an indicator of infection
- Bacteria - Also a possible sign of infection
- Crystals - May be a sign of presence of kidney stones
- Proteins - Product of kidney disorders
In many cases, results of a urinalysis are not a sole basis for diagnosis. It is up to your doctor to recommend other tests to determine your condition and define the next steps.
2. Urine Protein Test - When kidney function continues to decline, albumin (a protein in the blood) levels increase because poorly functioning kidneys leak excess protein into the blood. Too much albumin can lead to proteinuria, where 150 mg of protein per day is excreted to the blood.
Your nephrologist may measure your albumin levels through an albumin-focused dipstick test (microalbuminuria test) and compare this number to your creatinine levels. This measurement is called the urine albumin-to-creatinine ratio (UACR). According to American Kidney Fund, a UACR of more than 30 mg/g can be a sign of kidney disease.
3. Microalbuminuria Test - Microalbuminuria refers to the above normal excretion of albumin into the urine. The purpose of this sensitive protein test is to measure the albumin levels in your urine. It can detect even the slightest hint of albumin and is done together with a creatinine test to get your UACR.
A regular microalbuminuria test is recommended for people who are at a greater risk of developing kidney disease, especially those with diabetes, high blood pressure, or those who have a family history of kidney disease.
This is because diabetes and high blood pressure can damage the kidneys, resulting in the excessive leakage of albumin into the urine. Your nephrologist will use this test to assess the extent of damage to your kidneys.
Microalbuminuria test results are measured in terms of milligrams (mg) of albumin leakage into your urine over 24 hours. Here’s what albumin levels generally tell you about your kidney health:
- Less than 30mg of albumin - Normal
- 30 to 300mg - Microalbuminuria, and may be a sign of early CKD
- Greater than 300mg - Macroalbuminuria, a possible indication of advanced-stage CKD or end-stage renal disease (ESRD)
4. Creatinine Clearance - Creatinine is the waste product generated when we use our muscles. The creatinine clearance refers to the rate (in milliliters per minute) at which the kidneys can “clear” the blood of creatinine. Normal creatinine clearance depends on a person’s age, gender, race, height, and weight.
On average, the creatinine clearance is 120mL per minute in healthy young men, and 95mL per minute in young women. This means their kidneys can make 95 to 120mL of blood creatinine-free each minute. Creatinine clearance rate is also used to determine your eGFR since it cannot be measured directly.
Nephrologists look at creatinine levels and creatinine clearance rates to examine kidney function. As kidney function declines, creatinine clearance rate decreases. Routine eGFR or creatinine clearance tests help you to closely monitor your kidney function over time.
If you have low eGFR or creatinine clearance, your nephrologist will recommend ways to address this. If your CKD is caused either by diabetes or high blood pressure, the urgent steps you need to take are to follow a kidney-friendly diet, exercise, and take medications to control your blood sugar and blood pressure levels.
If you’ve already been diagnosed with CKD, expect that you will undergo some or all of these tests to track the development of your condition. The results from these exams will give your healthcare team a deeper insight into your kidney health so they can create a treatment plan that’s tailored to your unique condition.
Feel free to ask your nephrologist which tests are required and how often they will be done. Discuss with them your results. Ask them for practical steps to improve your results and how you can manage your condition for the long term.
Understanding Your Lab Values
Lab Values Explained
Protein in Urine
Urine Dipstick Testing: Everything You Need to Know
Creatinine and Creatinine Clearance Blood Tests https://www.webmd.com/a-to-z-guides/creatinine-and-creatinine-clearance-blood-tests#2