Creatinine is an indicator of kidney function. In this article, we discuss how it is produced, disposed of, as well as why it is an important indicator of kidney disease or reduced kidney function. We’ll also take a look at the less commonly talked about low creatinine levels.
What is Creatinine?
Creatinine is a waste product created from the normal wear and tear of muscles . It is produced from creatine, a protein needed to generate the energy for muscle contractions . The consumption of cooked meat can also introduce it to the body.
Creatinine production essentially reflects lean body mass, and because this mass changes little from day to day, the production rate is also fairly constant. Women, children, and older people tend to have lower levels of creatinine compared to adult men because they have less muscle mass .
Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood into the urine. When kidneys aren’t working properly, creatine remains in the blood and builds up. That is why blood levels are usually a good indicator of how well your kidneys are working [3, 1].
Creatinine levels can be tested in isolation, or as a part of your basic metabolic panel (BMP) or your comprehensive metabolic panel (CMP).
An Indicator of Kidney Function
Kidneys are the organs that filter the blood and remove toxic substances and excess water. This filtering cleans the blood and maintains a constant stable environment in the body (homeostasis) .
Creatinine, like other waste molecules, enters the kidneys and gets filtered in specialized compartments (glomeruli). After filtering, it is discarded in the urine .
When kidneys don’t function well, less creatinine gets filtered out from the blood, and blood creatinine levels increase. Kidney function can be estimated by measuring the creatinine clearance (inconvenient) or by looking at creatinine levels in the blood (easier and more affordable) .
The most direct method for measuring creatinine clearance is the collection of urine samples for a time period of 24 hours and a blood sample. Alternatively, a formula that uses the blood levels of creatinine, age, weight, and gender can also be used to calculate clearance .
Despite the method of calculation used, the value of creatinine clearance shows how much gets removed from the blood by the kidneys and this provides an estimate of kidney function .
Although creatinine clearance provides one of the most direct and cost-free methods to estimate kidney function, its measurement has several disadvantages [6, 7]:
- requires the continuous collection of samples for 24 hours
- can be miscalculated if the urinal samples are not collected properly
- varies depending on the site of collection
- varies depending on the day of collection
Blood Creatinine Levels
A blood creatinine measurement is easy to do, compared to creatinine clearance.
However, although high creatinine levels in the blood are often associated with reduced kidney function, other factors can also increase or decrease creatinine levels. That’s why your doctor will interpret this test, taking into account your medical history, signs, symptoms, and other test results.
For a couple of decades now, eGFR or estimated glomerular filtration rate, is routinely calculated based on creatinine levels. eGFR gives a more accurate assessment of kidney function compared to blood creatinine.
Normal Blood Creatinine Range
Creatinine levels increase with muscle mass. Other factors, such as age, sex, ethnicity, diet, etc., also affect its production [8, 9].
The normal blood creatinine range is around:
- Men: 0.6 to 1.2 mg/dL (milligrams per deciliter); 53 to 106 μmol/L (micromoles per liter)
- Women: 0.5 to 1.1 mg/dL; 44 to 97 μmol/L
Levels may vary slightly between labs, due to differences in equipment, techniques, and chemicals used.
A normal test doesn’t mean that kidney disease is absent. Your doctor will interpret your results in conjunction with your medical history and other test results, such as glomerular filtration rate (eGFR), blood urea nitrogen (BUN), phosphate, calcium, sodium, potassium, and glucose.
High Blood Creatinine Levels
As the kidneys become impaired for any reason, they start having troubles filtering out waste products and toxins. As a result, creatinine levels in the blood increase. However, there are also several other factors that can increase creatinine levels.
A high level of creatinine will not cause symptoms on its own. Even if you have above-normal levels you may not notice a change. However, high creatinine is often caused by an underlying disease that affects kidney function, such as kidney disease, diabetes, high blood pressure, or hypothyroidism. In these cases, you will experience the symptoms of the underlying disease/disorder. Work with your doctor to treat any underlying condition.
Causes of High Creatinine
Causes listed below are commonly associated with high creatinine. Work with your doctor or another health care professional to get an accurate diagnosis. Your doctor will interpret this test, taking into account your medical history and other tests. A result that is slightly higher may not be of medical significance, as this test often varies from day to day and from person to person.
1) Kidney Disease
Creatinine is most commonly checked to measure kidney function. If creatinine is high, it may indicate kidney disease or impaired kidney function [10, 11].
Diabetes can cause injury in the blood vessels of the kidneys which in turn reduces the ability of the kidneys to filter the blood from waste products including creatinine .
2) Diet High in Protein
Studies have found that a protein-rich diet elevates the levels of blood creatinine both in healthy and individuals suffering from kidney failure [13, 14].
Also, eating cooked meat just before the test can cause a spike in creatinine levels. This happens because cooking converts the creatine present in meat (which is muscle) into creatinine [15, 16].
Exercise can increase creatinine short-term, due to muscle damage, or long-term, due to an increase in muscle mass [15, 17].
Studies in healthy individuals show a direct correlation between muscle mass and the levels of blood creatinine. This correlation is significant for both adult men and women .
4) Creatine Supplements
Supplementing with creatine increases creatinine levels in the blood [18, 15].
Hypothyroidism decreases kidney function and blood flow to the kidneys, which results in elevated creatinine levels .
Levels can normalize rapidly with thyroid hormone replacement after short periods of hypothyroidism, but may normalize slower after more prolonged periods of severe hypothyroidism .
6) Urinary Tract Obstruction
A blocked urinary tract can cause kidney injury, which increases creatinine in the blood [21, 22].
7) Heart Failure
There is a bidirectional relationship between kidney disease and heart disease, where each condition increases the risk of the other.
In heart failure, blood flow to the kidneys is reduced, which decreases creatinine filtration and increases creatinine levels in the blood [23, 24].
8) Some Drugs
Please discuss your medications with your healthcare provider. They will assess your test results taking into account your medications and other relevant factors to determine whether a result outside of the reference range means something for you.
Contact your doctor or pharmacist if you notice medication side effects such as tiredness, dry or itchy skin, blood in your urine, or anything else out of the ordinary.
Call your doctor for medical advice about side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.
With this in mind, the following medications may increase creatinine levels in some people:
- Antibiotics, such as aminoglycoside, cephalosporin, amphotericin B, trimethoprim/sulfamethoxazole (Bactrim, Cotrim, Septra) and cefoxitin (Mefoxin) [25, 26]
- Antihistamines that decrease stomach acid production, such as cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac) 
- NSAIDs, including aspirin, ibuprofen, indomethacin, and naproxen [27, 25, 28, 29]
- Cyclosporine, an immunosuppressant [30, 31]
- Anticonvulsants, including phenacemide (Phenurone) 
- Acetaminophen (Tylenol, Panadol, paracetamol) 
Decreasing Blood Creatinine
Work with your doctor to find out what’s causing your high creatinine and to treat any underlying conditions.
If you have kidney disease, your doctor may prescribe medication to manage your symptoms. Some drugs used in kidney disease patients include water pills (diuretics), medications for lowering high blood pressure, erythropoietin, and others.
Dialysis is a common treatment for people with kidney disease. This medical procedure is used in people whose kidneys can’t remove waste products effectively.
If you have kidney issues, you may need to limit your protein intake. Kidneys must work harder when there’s more protein in the diet and a high-protein diet can further aggravate kidney function .
Similarly, if your kidneys are not working properly, your blood phosphorus and potassium may increase, in which case you may need to limit their intake. Discuss an appropriate diet to protect your kidney health with your doctor [35, 36].
Finally, if kidney damage is a concern, it’s important to monitor and manage your blood pressure to prevent further kidney damage [37, 38, 39].
Discuss the additional strategies listed below with your doctor. None of these should ever be done in place of what your doctor recommends or prescribes!
High blood creatinine can be a result of dehydration. It’s important to stay hydrated, by drinking around two liters of water a day .
2) Weight Loss
A study of 154 overweight or obese men suggests that weight loss can improve kidney health and decrease creatinine levels .
A fiber-rich diet improves kidney health and can lower blood creatinine levels .
Fruits, veggies, whole grains, and legumes are good sources of fiber.
Low Blood Creatinine
Low blood creatinine levels are not always a concern. They can just indicate a diet low in protein . Your doctor will interpret your results, taking into account your medical history, symptoms, and other test results.
Causes of Low Creatinine
Causes listed below are commonly associated with low blood creatinine. Work with your doctor or another health care professional to get an accurate diagnosis.
1) Malnutrition/Lack of protein
Malnutrition, and specifically lack of protein, decrease muscle mass, which decreases blood creatinine levels .
2) Extreme Weight Loss
Extreme weight loss has a similar effect. Loss of muscle mass means that less creatinine is released from muscles into the blood [41, 45].
3) Muscle Wasting
Muscle wasting in illness or aging is commonly associated with lower creatinine levels [11, 43, 46].
Often patients lose a great part of their muscle mass within the first week of hospitalization which results in lower levels of blood creatinine .
If those who also suffer from kidney disease (which would increase the levels of creatinine), the levels of creatinine might be falsely within the normal range. Thus, muscle wasting can be a factor that interferes with the proper diagnosis of kidney failure .
4) Limb Amputation
Lower creatinine is normal in amputees, because they have less total muscle mass .
Several studies have found a link between heavy drinking and alcoholism with lower creatinine levels [49, 50].
6) Liver Disease
People who have liver disease can have low blood creatinine due to decreased production of creatine in the liver. Creatine is needed to make creatinine in the muscles. Altered kidney function and muscle wasting due to illness may also play a part .
Creatinine is normally lower in pregnancy .
Hyperthyroidism can increase blood flow through the kidneys, and thereby decrease blood creatinine levels .
Increasing Blood Creatinine
The most important thing is to work with your doctor to find out what’s causing your low creatinine and to treat any underlying conditions.
Discuss the additional lifestyle changes listed below with your doctor. None of these strategies should ever be done in place of what your doctor recommends or prescribes!
Adjust your diet if needed! Make sure you are well-nourished and your diet contains enough protein. If you have trouble getting enough protein from your diet, discuss a protein supplement with your doctor.
If you’re inactive, increasing physical activity can help build muscles and increase creatinine levels [15, 51].