Creatinine is a waste product normally excreted by the kidneys, which is passed in urine. While creatinine itself is caused by muscle metabolism, its presence in urine indicates how well the kidneys are functioning. Your doctor may want to test your creatinine clearance rate, which is a good indicator of whether or not you have kidney disease. High creatinine levels may also indicate other conditions your physician may want to investigate. Read on to learn more about testing for creatinine, why levels may be high or low, and when you should be concerned.
How Is Creatinine Measured?
A creatinine urine test is not a test commonly given at routine physicals or checkups. Your symptoms may implore your doctor to order the test to check for kidney disease or other problems. A creatinine test is not a normal urine test, where a patient urinates in a cup for a single result. Creatinine levels can vacillate throughout the day, so your doctor will want to check your urine for 24 hours. For this test, you will have to collect every urination at home for 24 hours and return the sample to your doctor. Because urine creatinine levels may vary based on size, weight, gender, and other factors, your doctor may also want to order a serum creatinine test, which is a blood test that will look for creatinine levels in the blood. Serum tests often use glomerular filtration rate (GFR) tests, which measures serum creatinine but also takes into account other contributing factors, such as age and gender.
What Are Normal Creatinine Results?
Normal results may vary by laboratory, but generally speaking, females in the normal range have a value of 0.6–1.6 g/day or 5.3–14.0 mmol/day, and males have a value of 0.8–1.8 g/day or 7.0–16.0 mmol/day for normal results.
What Are Low and High Creatinine Levels?
A high creatinine level is a reading above the normal range for males and females. However, because of other contributing factors, a high (or low) value does not indicate a problem — it just warrants further testing. However, a creatinine level that falls outside the norm may indicate an issue, typically kidney disease. Other conditions associated with high creatinine levels include kidney stones, muscular dystrophy, and myasthenia gravis. Those who have diabetes may also have high or low levels. To check for these conditions, your doctor will order more comprehensive testing.
What Are Symptoms That May Prompt a Creatinine Test?
It’s likely that your doctor will order a creatinine test because you presented with certain symptoms. These may include dehydration, jaundice (yellowing of the skin or eyes), fatigue, swelling of the extremities, confusion, and shortness of breath. Nausea and vomiting may also be present.
What Are Other Causes of Abnormal Readings?
An issue with a creatinine test is that the results may vary widely based on other conditions. For instance, elderly persons may have less creatinine than younger persons, and this isn’t necessarily indicative of disease. Also, severe weight loss or malnutrition may affect readings. Muscular young men and women may have higher-than-normal levels because of their athleticism and muscle function.
What Other Tests May Be Ordered?
Your doctor will likely order a serum creatinine test if your urine creatinine test had abnormal levels. Another common follow-up test is the blood urea nitrogen (BUN) test, which checks for urea. Abnormal levels of urea more strongly point to kidney disease, and this can aid your doctor in diagnosing you. If kidney disease is suspected, it’s likely imaging tests, such as a CT scan or ultrasound, will be ordered.