Serum creatinine is a common blood test that measures the amount of creatinine in your bloodstream. Creatinine is a normal waste product made when your muscles use energy (a routine part of muscle metabolism). Healthy kidneys filter creatinine out of the blood and remove it through urine.

This test is a key marker of kidney function and overall renal health. When the kidneys are not filtering well, creatinine levels can rise. Your serum creatinine result is often used—along with your age, sex, and sometimes race and body size—to estimate your glomerular filtration rate (GFR), also called eGFR. GFR describes how effectively your kidneys are filtering waste and extra fluid.

In plain language, results are generally interpreted like this:

• Higher-than-expected creatinine may suggest reduced kidney filtration (lower GFR/eGFR), which can happen with acute kidney injury, chronic kidney disease, dehydration, or blockage of urine flow. Certain medications and supplements can also raise creatinine.

• Lower-than-expected creatinine is less commonly a kidney issue and may be related to low muscle mass, pregnancy, or poor nutrition.

Because creatinine is influenced by muscle mass, diet (especially large amounts of cooked meat), hydration, and some medicines, your clinician interprets the value in context and may repeat the test or pair it with other labs such as blood urea nitrogen (BUN), urine albumin-to-creatinine ratio (ACR), or a urinalysis.

Serum creatinine is frequently ordered to evaluate kidney disease diagnosis, screen people at risk for kidney problems, and monitor known kidney conditions over time. It may be done as part of routine lab work or urgently when kidney function could be changing quickly.

Your clinician may order this test if you have symptoms or signs that could suggest kidney problems, such as:

• Swelling of the legs, ankles, feet, face, or around the eyes (fluid retention)

• Changes in urination (urinating less or more than usual, foamy urine, blood in urine, waking at night to urinate)

• Fatigue, weakness, nausea, poor appetite, or “brain fog” that could occur when waste builds up

• High blood pressure that is new or hard to control

• Flank/back pain or symptoms of urinary obstruction (in certain cases)

It is also commonly done if you have risk factors for reduced kidney function, including:

• Diabetes (a leading cause of chronic kidney disease)

• Hypertension (high blood pressure)

• Heart disease or history of stroke

• Age over ~60 or a family history of kidney disease

• Recurrent kidney stones or frequent urinary tract issues

• Autoimmune disease (e.g., lupus) that can affect the kidneys

• Use of medications that can affect kidneys or require kidney-based dosing (for example, NSAIDs like ibuprofen/naproxen, certain antibiotics, ACE inhibitors/ARBs, diuretics, lithium, chemotherapy drugs)

• Before imaging tests with IV contrast or before surgery, to ensure kidneys can handle the stress and to guide safe medication choices

Because serum creatinine helps estimate GFR, it’s central to staging and monitoring chronic kidney disease (CKD), adjusting medication doses, and tracking whether kidney function is stable, improving, or worsening.

• Chronic kidney disease (CKD)
• Acute kidney injury (AKI)
• Diabetic kidney disease (diabetic nephropathy)
• Hypertensive kidney disease (kidney damage from high blood pressure)
• Glomerulonephritis (inflammation of the kidney’s filtering units)
• Polycystic kidney disease (PKD)
• Urinary tract obstruction (e.g., enlarged prostate/BPH, kidney stones, tumors)
• Dehydration or severe volume depletion (can raise creatinine and lower GFR temporarily)
• Rhabdomyolysis (muscle breakdown that can injure kidneys)
• Chronic heart failure or poor circulation affecting kidney perfusion (cardiorenal syndrome)

• Monitoring kidney function and long-term renal health as part of preventive care
• Early detection and ongoing monitoring of chronic kidney disease (CKD) progression
• Tracking glomerular filtration rate (GFR/eGFR) to understand how well the kidneys filter waste
• Medication safety: ensuring correct dosing and reducing risk of drug-related kidney injury
• Diabetes and blood pressure management: assessing organ impact and preventing complications
• Pre-surgical or pre-procedure assessment (including before contrast imaging)
• General wellness lab screening when combined with other routine blood and urine tests