Creatinine blood test: What it measures and what your results mean

A creatinine blood test measures the amount of creatinine — a waste product from normal muscle breakdown — in your bloodstream. Healthy kidneys filter creatinine out of the blood and into urine, so the level in your blood is one of the most common indicators of how well your kidneys are working.¹

What is creatinine?

Your body makes creatine to fuel muscle activity. As muscles use that energy, they break creatine down into a waste product called creatinine, which travels through the blood to the kidneys. The kidneys filter creatinine out and excrete it in urine. Because production is relatively steady from day to day, blood creatinine levels are a useful — though imperfect — way to estimate kidney filtration.²

What does the creatinine blood test measure?

The serum creatinine test reports the concentration of creatinine in a small blood sample, usually drawn from a vein in your arm. Most lab panels report creatinine alongside an estimated glomerular filtration rate (eGFR), which is the preferred way to interpret kidney function:^1,3

• Serum creatinine in mg/dL or μmol/L — the raw concentration in your blood
• eGFR in mL/min/1.73m² — calculated from creatinine, age, and sex; estimates how much blood the kidneys filter per minute
• Creatinine clearance — calculated from a 24-hour urine collection plus blood creatinine, used in specific clinical situations

The National Kidney Foundation and Cleveland Clinic both note that eGFR is a more accurate reflection of kidney function than creatinine alone, because creatinine is influenced by muscle mass, hydration, and other non-kidney factors.^3,4

What is a normal creatinine level?

Reference ranges vary by lab and population, but typical adult ranges are:^2,5

• Men: roughly 0.6 to 1.2 mg/dL
• Women: roughly 0.5 to 1.1 mg/dL
• Children: 0.3 to 0.7 mg/dL (varies with age)

For eGFR, an adult value of 90 to 120 mL/min/1.73m² is generally considered normal. A persistent eGFR below 60 for three months or longer indicates chronic kidney disease (CKD). An eGFR below 15 indicates kidney failure and usually requires dialysis or transplant evaluation.^1,3

What does a high creatinine level mean?

A high creatinine level (or low eGFR) often signals reduced kidney filtration, but the cause isn't always kidney damage. Common reasons creatinine can be elevated include:^2,6

• Acute kidney injury (from dehydration, severe infection, contrast dye, or shock)
• Chronic kidney disease (frequently linked to diabetes and high blood pressure)
• Urinary tract obstruction such as kidney stones or an enlarged prostate
• High muscle mass — bodybuilders and athletes often have higher baseline creatinine
• A high-protein or creatine-supplement diet
• Intense exercise in the 24 to 48 hours before the test
• Medications such as certain antibiotics (trimethoprim), ACE inhibitors, ARBs, NSAIDs, or chemotherapy agents — some block creatinine secretion without actually changing kidney function

Because of these confounders, a single elevated reading is rarely diagnostic. Clinicians look at trends, eGFR, urine protein, and other tests to decide whether kidney disease is present.

What does a low creatinine level mean?

Low creatinine usually isn't a kidney problem. Common explanations include:²

• Low muscle mass (older adults, post-illness, or significant weight loss)
• Pregnancy, which increases blood volume and lowers creatinine
• Severe liver disease, which reduces creatine production
• A very low-protein or vegetarian diet

Who should have a creatinine test?

Your clinician may order a creatinine test as part of a routine basic or comprehensive metabolic panel, or for a specific reason, including:^1,5

• Annual screening if you have diabetes, high blood pressure, or a family history of kidney disease
• Before and during certain medications (chemotherapy, contrast imaging, ACE inhibitors)
• Symptoms that suggest kidney problems — swelling, foamy urine, decreased urination, or unexplained fatigue
• Pre-operative evaluation
• Monitoring known chronic kidney disease

How do you prepare for a creatinine test?

Most creatinine tests don't require fasting unless your clinician is also drawing a metabolic panel that requires it. Practical guidance:

• Avoid heavy exercise the 24 hours before the test if possible.
• Tell your clinician about any creatine or protein supplements you take.
• Stay hydrated as you normally would; severe dehydration can transiently raise creatinine.
• Bring a list of all medications and supplements.

How do you lower high creatinine?

Lowering creatinine starts with treating the underlying cause. If reduced kidney function is confirmed, common steps include:⁵

• Tightly controlling blood sugar in diabetes and blood pressure in hypertension
• Reviewing medications with your clinician — some need dose adjustment or substitution
• Avoiding NSAIDs (ibuprofen, naproxen) when possible
• Limiting protein and creatine supplements
• Treating dehydration, infection, or obstruction promptly

Don't try to "lower creatinine" on your own without working with a clinician — masking a result without addressing the cause can delay diagnosis of a serious problem.

Next steps

If you've had a recent creatinine result that's outside the normal range — or you have symptoms of a urinary tract or kidney issue — Solv can help you find a same-day urgent care or walk-in clinic that can repeat the test, evaluate symptoms, and refer you for further workup if needed.