What is creatinine?
Everyone has a certain level of serum creatinine in their blood. Creatinine is a natural byproduct of muscle use, caused by the breakdown of a chemical called creatine. Creatinine itself has no specific physiological function - it's just a waste product. It simply stays in the bloodstream until it reaches the kidneys, where it is filtered and excreted through the urine.
So, how does your body produce creatinine? It starts with creatine, which is primarily synthesized in the kidneys, pancreas, and liver. Creatine is transported to skeletal muscle by the bloodstream and stored in free and phosphorylated forms. However, creatine is primarily stored in its phosphorylated form, known as phosphocreatine or phosphocreatine. During exercise, the muscles convert stored creatine molecules into energy, which helps the muscles contract. After being used for energy, creatine is broken down into creatinine, which reenters the blood and travels to the kidneys.
Creatinine is released from the muscles and enters the bloodstream, where it is filtered at a relatively constant rate. Although creatinine won't actively benefit (or harm) your body, you can assess the health of your kidneys by measuring the amount of creatinine in your blood. For this reason, healthcare providers often use creatinine tests, along with other laboratory tests, such as blood urea nitrogen (BUN) tests, to monitor for chronic kidney disease (CKD) or kidney failure.
What is a good creatinine level?
Creatinine levels are measured in milligrams per deciliter (mg/dL). In most cases, the normal range for serum creatinine (found in the blood) in people with healthy kidneys is 0.7 to 1.3 mg/dL for adult men and 0.6 to 1.1 mg/dL for adult women.
However, there are many variables in normal levels of creatinine. "Normal" is a somewhat subjective term. Creatinine is produced by the breakdown of muscle, so your muscle mass and activity level can affect the amount of creatinine in your blood. Taylor Graber, MD, an anesthesiologist and founder of ASAP IV, said that in order to accurately measure blood creatinine levels, physicians will first assess these various factors to establish a baseline. "Creatinine level assessment begins with obtaining a population baseline to assess what a 'normal level' should be," Dr. Graeber said. "It depends on age, race, sex, and body size. Once these values normalize, a change in that range could indicate a kidney abnormality."
Healthcare providers like to keep an eye on creatinine levels for a variety of reasons. If you have or currently have kidney disease, kidney damage, diabetes, or other conditions that affect your kidneys, or are taking medications that may affect your kidneys, your healthcare provider may order periodic creatinine measurements to monitor your kidney function. The most common methods of testing are through blood and urine.
creatinine blood test
Creatinine from the blood is called serum creatinine and can be measured with routine blood tests. "When kidney function is impaired, there is less creatinine to clear, which leads to higher creatinine levels in the blood," Dr. Graeber explained. "While this test doesn't directly tell you how well your kidneys are functioning, it can track changes over time."
A healthcare provider can use a creatinine blood test to measure your serum creatinine level, which can be used to estimate your glomerular filtration rate (GFR). Measuring GFR levels is critical for diagnosing kidney failure or chronic kidney disease. Your GFR can be measured directly, but testing can be complex and time-consuming. Instead, healthcare providers can use serum creatinine levels to estimate GFR. To calculate your estimated GFR (eGFR), your healthcare provider will also consider other factors, such as:
age
gender
weight
high
Race
Urine creatinine test
The other most common way to measure creatinine levels is through a 24-hour urine collection. Why 24 hours? Exercise, diet, and hydration all affect creatinine, so your creatinine levels may fluctuate throughout the day. Therefore, your healthcare provider will require multiple urine samples over a 24-hour period to accurately assess kidney function.
As you might imagine, the test involves collecting all of your urine over a 24-hour period and giving it to your healthcare provider. Based on the results, your healthcare provider can determine how well your kidneys are filtering creatinine into your urinary tract.
