What is a Creatinine blood test?

A creatinine blood test measures the level of creatinine in the blood. Creatinine is a waste product that forms when creatine, which is found in your muscle, breaks down. Creatinine levels in the blood can provide your doctor with information about how well your kidneys are working.

Each kidney has millions of small blood-filtering units called nephrons. The nephrons constantly filter blood through a very tiny cluster of blood vessels known as glomeruli. These structures filter waste products, excess water, and other impurities out of the blood. The toxins are stored in the bladder and then removed during urination.

Creatinine is one of the substances that your kidneys normally eliminate from the body. Doctors measure the level of creatinine in the blood to check kidney function. High levels of creatinine may indicate that your kidney is damaged and not working properly.

Creatinine blood tests are usually performed along with several other laboratory tests, including a blood urea nitrogen (BUN) test and a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). These tests are done during routine physical exams to help diagnose certain diseases and to check for any problems with your kidney function.

Why is a creatinine blood test done?

Your doctor may order a creatinine blood test to assess your creatinine levels if you show signs of kidney disease. These symptoms include:

  • Fatigue and trouble sleeping
  • A loss of appetite
  • Swelling in the face, wrists, ankles, or abdomen
  • Lower back pain near the kidneys
  • Changes in urine output and frequency
  • High blood pressure
  • Nausea
  • Vomiting

Kidney problems can be related to different diseases or conditions, including:

  • Glomerulonephritis, which is an inflammation of the glomeruli due to damage
  • Pyelonephritis, which is a bacterial infection of the kidneys
  • Prostate disease, such as an enlarged prostate
  • Blockage of the urinary tract, which may be due to kidney stones
  • Decreased blood flow to the kidneys, which may be caused by congestive heart failure, diabetes, or dehydration
  • The death of kidney cells as a result of drug abuse
  • Streptococcal infections, such as poststreptococcal glomerulonephritis

Aminoglycoside medications, such as gentamicin (Garamycin, Gentasol), can also cause kidney damage in some people. If you’re taking this type of medication, your doctor may order regular creatinine blood tests to make sure your kidneys remain healthy.

How do I prepare for a creatinine blood test?

A creatinine blood test doesn’t require much preparation. Fasting isn’t necessary. You can and should eat and drink the same as you do normally to get an accurate result.

However, it’s important to tell your doctor about any prescription or over-the-counter (OTC) medications you’re currently taking. Some drugs may increase your creatinine levels without causing kidney damage and interfere with your test results. Let your doctor know if you take:

  • Cimetidine(Tagamet, Tagamet HB)
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin (Bayer) or ibuprofen (Advil, Midol)
  • Chemotherapy drugs
  • Cephalosporin antibiotics, such as cephalexin(Keflex) and cefuroxime (Ceftin)

Your doctor may ask you to stop taking your medication or to adjust your dosage before the test. They’ll also take this into consideration when interpreting your test results.

What do my creatinine blood test results mean?

Creatinine is measured in milligrams per deciliter of blood (mg/dL). People who are more muscular tend to have higher creatinine levels. Results may also vary depending on age and gender.

In general, however, normal creatinine levels range from 0.9 to 1.3 mg/dL in men and 0.6 to 1.1 mg/dL in women who are 18 to 60 years old. Normal levels are roughly the same for people over 60.

High serum creatinine levels in the blood indicate that the kidneys aren’t functioning properly.

Your serum creatinine levels may be slightly elevated or higher than normal due to:

  • A blocked urinary tract
  • A high-protein diet
  • Dehydration
  • Kidney problems, such as kidney damage or infection
  • Reduced blood flow to the kidneys due to shock, congestive heart failure, or complications of diabetes

If your creatinine is truly elevated and it’s from an acute or chronic kidney injury, the level won’t decrease until the problem is resolved. If it was temporarily or falsely elevated due to dehydration, a very high-protein diet, or supplement usage, then reversal of those conditions will lower the level. Also, a person receiving dialysis will have lower levels after a treatment.

It’s uncommon to have low levels of creatinine, but this can occur as a result of certain conditions that cause decreased muscle mass. They’re usually not any cause for concern.

EGFR (Glomerular Filtration Rate)

What is a glomerular filtration rate test?

Your kidneys are your body’s main filtration system. They remove waste products from your blood and excrete them via your urine. Glomeruli are the small filters inside your kidneys. If your kidneys aren’t working properly, your glomeruli won’t filter as efficiently. Your doctor may order a glomerular filtration rate (GFR) test if they suspect your kidneys aren’t working properly. This is a simple blood test.

Why do I need a glomerular filtration rate test?

The GFR test can indicate how well your kidneys are functioning. Your doctor may order the test if you have symptoms related to kidney disease or if they want to test the effectiveness of a particular treatment. According to the American Association for Clinical Chemistry, examples of kidney disease symptoms include:

  • Unexplained body swelling
  • Foamy urine
  • Difficulty urinating
  • Mid-back pain

Early intervention is vital to preventing further kidney damage. Your doctor may recommend a GFR test if you’re taking medications that can affect your kidney function or if you have any of the following conditions:

  • Diabetes
  • Recurring urinary tract infections
  • Hypertension
  • Heart disease
  • Difficulty with urination
  • Blood in the urine
  • Kidney stones
  • Polycystic kidney disease
  • Kidney failure

If you’ve been diagnosed with kidney disease, the GFR test can help determine how well your kidneys are functioning.

If you have a family history of kidney disease, your doctor may want to run a GFR test to get a sense of the current state of your kidneys.

How is a glomerular filtration rate test performed?

A GFR test is a simple blood test that doesn’t require you to do anything to prepare.

A blood sample will be taken by drawing blood from your arm. Because there’s a specific formula used to calculate GFR, you may also need to provide your:

  • Age
  • Sex
  • Race
  • Height
  • Weight

A laboratory specialist will take these factors into account to calculate the most accurate GFR.

A eGFR test is a simple blood test that doesn’t require you to do anything to prepare. The test will measure the amount of the waste product creatinine in your blood. The test is done to determine how well your kidneys are working. Based on your GFR results, your doctor can determine how much, if any, kidney damage you have.



Original sources


Creatinine. (2017).

Creatinine (blood). (n.d.).

Kozukawa A, et al. (2013). Acute post-streptococcal glomerulonephritis with acute kidney injury in nephrotic syndrome with the glomerular deposition of nephritis-associated plasmin receptor antigen. DOI:

About eGFR. (n.d.) – sthash.NlGqu3oV.dpbs

eGFR. (2015, October 29)