Creatinine Test

Overview

Creatinine is a waste product made when muscles use energy. The kidneys remove creatinine from the blood by filtering it out through urine. Health professionals often test blood and urine creatinine levels to assess kidney function. Related tests, such as blood urea nitrogen (BUN), may also be used to evaluate kidney health.

Term	Description
Creatinine	Waste from muscle tissue energy use
Kidney Function	How well kidneys filter waste
Blood Creatinine Level	Amount of creatinine present in the blood
BUN	Another marker for kidney diagnostics

Reasons for Testing

Doctors use creatinine tests to check how well the kidneys are working. This test often helps find kidney disease, especially in people with diabetes, high blood pressure, or chronic kidney disease (CKD).

It can also show if kidney problems are getting worse or if treatments such as dialysis are working. Other reasons for this test:

• Monitor for damage from some medicines.
• Check for issues after a kidney transplant.
• Watch for complications in conditions like heart disease, kidney failure, or kidney infections.

Steps Before the Test

Preparing for a creatinine test may involve adjusting diet, supplements, and hydration. In some cases, a doctor may ask the patient not to eat overnight—this is called fasting.

People might need to avoid eating meat before the test, as it can temporarily raise creatinine levels. Those who take creatine supplements to support muscle growth should stop using them, since they can also affect test results.

For a urine-based creatinine test, patients may be asked to collect all urine over 24 hours using special containers. It’s important to drink enough water, unless advised otherwise, because dehydration can affect levels of both creatinine and albumin in the results.

What to Expect During Testing

A creatinine blood test usually takes place in a clinic. A health worker uses a needle to draw a small amount of blood from your arm. For a urine creatinine test, you may give one urine sample at the clinic or collect your urine at home for a full day.

Test Outcomes

Blood Creatinine Value

Serum creatinine shows how well the kidneys remove waste from the blood. In healthy adults, this value should stay fairly steady. Results appear in milligrams per deciliter (mg/dL) or micromoles per liter (mmol/L).

Group	Typical Range (mg/dL)	Typical Range (mmol/L)
Adult men	0.74 – 1.35	65.4 – 119.3
Adult women	0.59 – 1.04	52.2 – 91.9

If blood creatinine levels go up, this can be a clue that the kidneys are not working as they should. The health care provider will look at these results along with other lab and health findings.

Estimated Kidney Filtration Rate (GFR)

You can calculate the estimated glomerular filtration rate (eGFR) with a blood creatinine test and other details such as age and sex. This number shows how efficiently the kidneys clean the blood each minute.

A GFR below 60 may be a sign of kidney disease, even if a person is not having symptoms. Tracking eGFR over time helps doctors see if kidney function is getting worse or staying the same. People with higher GFR usually have healthier kidneys. Here is a quick guide:

• GFR of 60 or Above: Generally considered normal.
• GFR Below 60: May suggest underlying kidney disease.
• GFR of 15 or Less: Points to possible kidney failure.

Screening for Creatinine Excretion

Creatinine clearance checks how quickly the kidneys filter creatinine from the blood into the urine. This test uses results from both a blood sample and urine collected over a set period, usually 24 hours.

Sometimes, you may collect urine for a shorter time, but getting the timing right is important. Lower than expected test results for a person’s age group may mean the kidneys are losing function.

Ratio of Albumin to Creatinine in Urine

The albumin-to-creatinine ratio (UACR) compares the amount of albumin, a type of protein, to creatinine in a urine sample. Healthy kidneys generally do not let much albumin pass into urine.

Group	Expected Value (mg/g)
Adult men	Less than 17
Adult women	Less than 25

Findings higher than these values may signal kidney problems. For example, people with diabetes who begin to develop kidney damage—a condition known as diabetic kidney disease—may show a high urine albumin-to-creatinine ratio (UACR). Providers may repeat this test to confirm the results or monitor changes over time.