When you go for your yearly check-up, you’ll likely have a routine blood test for creatinine. In some cases, your doctor may order a urine creatinine clearance test, as well. High blood creatinine levels can indicate that your body has a reduced ability to get rid of waste products — an important kidney function.
Even if you feel fine now, an elevated blood creatinine result may be a cause of concern. And if you’ve been infected with COVID-19, your creatinine levels should be periodically checked.
Below, medical experts discuss the causes and symptoms of abnormal creatinine levels, when it’s time to worry and how to act now to prevent future kidney problems.
Your kidneys are a pair of bean-shaped organs with one located on each side of the spine, right beneath your ribcage. Kidneys are part of the urinary tract and have several system-wide functions:
— Filtering the blood to remove waste and excess fluid through the urine.
— Creating hormones that control blood pressure, develop red blood cells and keep bones strong.
Blood continuously flows into the kidney through the nephrons. Each kidney contains roughly one million nephrons. These tiny units contain a glomerulus, which does the filtering, and a tubule, which returns vital minerals and nutrients to the blood while removing excess fluid and wastes.
Kidney disease involves a gradual loss of kidney function. As the kidneys progressively lose their filtering ability, toxic levels of fluids, minerals and waste build up in the body.
In the early stages, kidney disease is ‘silent’ with few signs or symptoms, often preventing it from being detected until it’s advanced. If caught early, underlying causes of kidney disease — such as high blood pressure, diabetes, polycystic kidney disease (an inherited, chronic condition that causes fluid-filled cysts to form in the kidney) and inflammation of the glomeruli — can be treated.
Unfortunately, advanced kidney damage can progress to kidney failure, which means patients must eventually require dialysis or have a kidney transplant.
[See: Kidney Cancer Symptoms.]
“Creatinine is basically a byproduct of skeletal muscle breakdown,” says Dr. Amy Yau, a nephrologist at the Ohio State University Wexner Medical Center. “Creatinine can come from a variety of sources — the body can make it by itself, it can come from the diet or it can come from cell breakdown.”
Creatinine levels represent one way of assessing how well the kidneys are working. “We use creatinine to help us estimate kidney function because creatinine is what’s called ‘freely filtered,'” Yau explains. “It’s freely filtered by the kidney, and so we have an idea of what a normal creatinine should be in most people with intact kidney function.”
However, creatinine levels alone don’t tell the whole story. They’re used in conjunction with various other laboratory results including:
— Glomerular filtration rate. GFR is an estimate of how much blood passes through the glomeruli each minute. “We typically take creatinine and we plug it into an equation,” Yau says. “There are multiple different types of equations to estimate the GFR — which is what really tells us how well the kidney is filtering. That GFR equation is stratified based on your age. So, what might be a normal creatinine for a person who is 20 years old may be different or a not-so-worrisome creatinine in a person who’s 80 years old.”
— Blood urea nitrogen. BUN measures the amount of urea nitrogen — a waste product of protein digestion — in the blood. The protein waste is excreted by healthy kidneys. BUN is an indirect marker of kidney function, Yau says, but it can be affected by other things, too, like dehydration, certain medications and a high-protein diet. So, doctors take the creatinine, GFR and BUN results together to give them an idea of how the kidney is doing.
Creatinine in the blood is measured in units called milligrams per deciliter, or mg/dL. Normal blood creatinine levels, which fall into a range, aren’t exactly the same for everyone. “The normal creatinine is generally between 0.7 and 1.1 or 1.2,” says Dr. Ziyad Al-Aly, a clinical epidemiologist at Washington University School of Medicine in St. Louis.
“When creatinine is high, it actually means that the kidney is not doing very well,” Al-Aly says. “It’s not really getting rid of all the toxins in the body. When creatinine is low or normal, that’s when you can think that the kidney is doing its job filtering the blood and working fine.”
Certain factors affect an individual patient’s normal creatinine levels. Because creatinine is made by your skeletal muscle cells, your baseline creatinine is affected by your size and muscle mass. Bodybuilders might have higher creatinine levels, whereas women tend to have slightly lower creatinine levels than men. Having had amputations would also affect baseline creatinine, Yau notes. “In general, I typically tell my patients that a creatinine of about 1.0 is considered normal,” she says.
Stability is another factor to consider — whether creatinine levels are changing quickly, Al-Aly says. “So, even if that creatinine is 1.0 or close to 1.0, if two months ago it was 0.5 and now it’s 1.0, that’s kind of a big change,” he says. In contrast, if the creatinine level has been stable at 1.0 for month after month, for years, he says, “That makes me feel a little bit more reassured.”
For abnormally high creatinine, Al-Aly says, “There is no ‘panic number,’ per se.” Instead, “We look at things dynamically,” he explains. “So if it’s a jump — like somebody’s normal creatinine is 1.0 and then all of a sudden it jumps to 5.0 — I would be concerned. The magnitude of the change is what we’re looking at.”
It’s important for patients to not confuse creatinine and glomerular filtration rate trends, Al-Aly notes. GFR works in the opposite way — a good number can go up to 100%, he says. When GFR is high that indicates good kidney function — everything’s fine. Lower GFR suggests there’s decreased kidney function and is an indication of disease.
Urine Creatinine Clearance
If your creatinine blood test result is elevated, your doctor might want more information. You may leave the office with either a handheld urinal (for men) or a urine collection ‘hat’ (for women) and an opaque plastic jug, with a homework assignment to collect your urine for the next 24 hours to provide a follow-up sample for further testing.
You’ll also be asked to drink eight glasses of fluid during that period to provide an adequate sample to measure creatinine clearance, or how fast your kidneys clear creatinine from your body. Hospitalized patients sometimes have a 24-hour urine collection done as part of their inpatient care.
Significantly high creatinine levels or upward trends would trigger a comprehensive diagnostic workup to determine the underlying causes.
Low Creatinine Levels
In general, below-normal creatinine levels are benign. However, very low levels can be a sign of malnourishment. Creatinine levels might be lower in these cases:
— Pregnancy. Plasma is the largest part of your blood. “Creatinine is a concentration,” Yau explains. “If your plasma volume is increased because you’re pregnant and carrying a baby, then your creatinine (level) will be falsely low.”
— Vegetarianism. “Sometimes vegetarians who don’t have a high-meat or high-protein diet don’t have a lot of creatinine,” Yau says.
— Muscle loss. A very thin, frail person, such as a nursing home resident who has lost a lot of muscle mass, can have extremely low creatinine levels, such as 0.2 or 0.3 mg/dL, Al-Aly says. “It’s not an indication that the kidney is doing a great job,” he points out. “It’s an indication that they don’t even have any muscle left over to even make creatinine for us to measure.”
Kidney Problems: Potential Causes
Medical conditions and other risk factors for kidney disease include:
— Diabetes. High blood sugar can damage blood vessels and nephrons in the kidney over time.
— High blood pressure. Uncontrolled hypertension can damage arteries around the kidneys.
— Heart disease. Changes in heart function may reduce the blood supply to the kidneys.
— Smoking. Smoking decreases blood flow to the kidney.
— Inflammatory kidney conditions: glomerulonephritis and interstitial nephritis.
— Inherited conditions like polycystic kidney disease.
— Ongoing urinary tract obstruction from kidney stones or an enlarged prostate. Blockages can increase pressure on the urinary tract.
— Persistent, recurring kidney infection, or pyelonephritis.
— COVID-19. Long COVID causes multiple effects including blood clots that may affect small vessels in the kidneys.
COVID-19 and Creatinine
COVID-19 can affect multiple organs including the lungs, brain, heart, liver and kidneys. Creatinine levels should be closely monitored for people with long COVID, a new study suggests.
Using a database of medical records kept by the U.S. Department of Veterans Affairs, the researchers evaluated de-identified information from more than 1.7 million healthy or infected veterans from March 2020 to mid-March 2021. Conducted by Al-Aly and colleagues, the study found that even people with mild cases are at increased risk of developing kidney damage and chronic or end-stage kidney disease.
The researchers used participants’ creatinine levels to determine trends in their glomerular filtration rates. The biggest decline in GFR occurred in intensive care unit patients, followed by other hospitalized patients and then patients with milder cases, in the study published in the November 2021 issue of the Journal of the American Society of Nephrology.
“What we know now about COVID-19 is it can lead to a lot of different manifestations in the long run,” Al-Aly says. “One of those manifestations is kidney disease, in the sense that it can actually lead to elevated creatinine in some people. It’s certainly happening in some people at six months or actually one year after the infection.”
Kidney Disease Symptoms
Although many people have no early symptoms of kidney problems, others may develop the following:
— Swelling (edema) in the lower legs or around the eyes.
— Nausea or vomiting.
— Shortness of breath from fluid around the lungs.
— Sleep problems.
— Unexplained weight loss.
— Weakness or fatigue.
— Dry, itchy skin.
— Difficulty concentrating.
— Peeing more or less than usual.
Once the underlying cause of decreased kidney function is determined, your health care team can develop a treatment plan to improve kidney function — such as starting medication to lower blood pressure or manage diabetes. You will likely need to see a kidney specialist, or nephrologist, for disease-specific treatment if chronic kidney disease itself is the problem.
Keep in mind that creatinine levels alone aren’t enough to pinpoint a specific health condition. “Creatinine is an imperfect marker of kidney function,” Yau says. “We use it because it’s easy but it’s only one piece we use to look at kidney function, in general. It’s a helpful marker, it’s easy to check but it’s not the end-all and be-all.”
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