Creatinine is a chemical compound, which serves as a waste product resulting from the energy-producing processes in the muscles. The kidneys filter creatinine from the blood and expel it in the form of waste products through urine. Hence, the creatinine test helps assess the efficiency of the kidneys in filtering waste products from the blood. 

What is a Creatinine test? What does the test measure?

A creatinine test means a blood or urine test that measures the amount of creatinine in the blood. It serves as a screening test to evaluate kidney function.

Purpose of the test

A creatinine test is conducted by collecting either a blood sample or a urine sample. Both urine and blood creatinine tests contribute to the assessment of kidney function in a patient. This evaluation can be a routine screening procedure or can serve to monitor the progression of kidney disease or determine the likelihood of its development. A creatinine urine test might also be performed as a component of a creatinine clearance test.

When should I get this test?

A healthcare provider or doctor might recommend a creatinine blood test or urine test if they suspect that poor kidney function is causing specific symptoms in the patient. They may also advise this test for other purposes:

• To diagnose the progression of kidney disease or assess its treatment.
• To screen for kidney disease, especially if the patient has diabetes or high blood pressure, which may elevate the risk of developing kidney disease.
• To monitor the impact of medicinal drugs on kidney function.
• To track the function of a transplanted kidney.

How to prepare for the test?

If a standard creatinine blood test is recommended by the doctor, this creatinine test requires fasting (not to eat overnight). For a creatinine urine test, the patient may be advised to collect urine and store it for 24 hours using containers provided by the clinic for testing.

The doctor might also provide additional guidelines for a specific period to prepare for the creatinine test. For instance, they may recommend discontinuing the use of supplements that could interfere with the accurate measurement of creatinine production and filtration in the kidneys.

How is it performed?

In the case of a serum creatinine test (blood creatinine test), a phlebotomist may draw blood from the patient by inserting a needle into a vein in the arm. For a urine creatinine test, the patient themselves may be required to provide a urine sample either at the clinic or collect it at home and return it after 24 hours.

Uses of Creatinine Test

The creatinine test is a common way to check how well your kidneys are working. It's used for:

• Kidney Health: To see if your kidneys are functioning properly by measuring the levels of creatinine, a waste product from muscles, in your blood.
• Detecting Kidney Diseases: To find issues like chronic kidney disease or acute kidney injury by identifying elevated creatinine levels.
• Adjusting Medication Dosages: To figure out the right doses of certain medications, especially those cleared by the kidneys, to avoid side effects.
• Before Surgeries or Procedures: To assess if your kidneys can handle medications or contrast agents used in medical procedures.
• Checking Dehydration and Muscle Problems: To see if dehydration or muscle disorders are affecting your creatinine levels.
• Estimating Kidney Filtration Rate: To estimate how much fluid your kidneys filter, known as the glomerular filtration rate (GFR), which is a key indicator of kidney function.

What to expect during a creatinine blood test? 

During a creatinine blood test, you can expect the following:

• Preparation: Typically, no special preparation is required. However, it's a good idea to inform your healthcare provider about any medications, supplements, or herbal remedies you are taking, as they might affect the test results.
• Blood Draw: The test involves a simple blood draw. A healthcare professional will clean the area, usually the inside of your elbow, with an antiseptic. They will then use a needle to draw a small amount of blood into a tube.
• Temporary Discomfort: You may feel a brief pinch or sting when the needle is inserted, but the discomfort is usually minimal. If you are nervous about needles, let the healthcare provider know in advance.
• Post-Draw Care: After the blood is drawn, a cotton ball or bandage will be placed on the puncture site. You may be asked to apply pressure to minimize bleeding and reduce the risk of bruising.
• Resuming Normal Activities: In most cases, you can resume your regular activities immediately after the blood draw. It's advisable to avoid heavy lifting or strenuous exercise with the arm that was used for the blood draw for a short period.
• Follow-Up Instructions: Your healthcare provider may provide specific instructions if any post-test care is needed or if further tests are required.
• Results: The blood sample is sent to a laboratory for analysis. Results are typically available within a few days, and your healthcare provider will discuss the findings with you.

What is the Creatinine test normal range?

The level of creatinine present in the body typically varies between females and males. Additionally, factors such as a person's body weight and muscle mass can influence this level. Generally, the creatinine level in a creatinine test may fall within the range of 0.7 to 1.3 mg/dL for men and 0.6 to 1.1 mg/dL for women.

Normal ranges can vary among different laboratories. The normal range parameters are typically provided in the test report, against which the patient's results are compared. A doctor is best equipped to interpret the results.

What do the creatinine blood test results mean?

Results from a creatinine blood test may show either high or low creatinine blood test levels, each with its own set of underlying causes.

Elevated creatinine levels in a creatinine test could signify:

• Urinary tract obstruction
• Dehydration
• Kidney diseases like damage, infection, reduced blood flow, or kidney failure
• Pregnancy-related issues, such as seizures or high blood pressure due to pre-eclampsia

A low creatinine level in a creatinine test might indicate conditions like:

• Malnutrition
• Reduced muscle mass resulting from nerve or muscle-related conditions.

The results from a urine or blood creatinine test are measured and interpreted in various ways, determining whether the creatinine level is high or low in a patient. The methods for measuring creatinine levels include the following:

• Serum creatinine level: Creatinine is filtered by the kidneys after being transported through the bloodstream as a byproduct of cellular processes in the muscles. The amount of creatinine present in the blood after filtration should remain stable. An elevated serum creatinine level above normal may indicate poor kidney function.
• Glomerular filtration rate (GFR): GFR refers to the rate at which blood is filtered in the kidneys through tiny structures called glomeruli. A GFR level lower than recommended may signal kidney disease progression and require monitoring.
• Creatinine clearance: The creatinine clearance test measures the kidneys' ability to filter out creatinine for excretion through urine. A urine sample is used to determine creatinine clearance. If the creatinine level in the sample is below recommended levels, it may indicate poor kidney function affecting blood flow to the kidneys.
• Albumin/ creatinine ratio: The albumin/creatinine ratio measures the amount of albumin present in a urine sample relative to the level of creatinine in the same sample. Albumin is a protein found in the blood that healthy kidneys normally do not filter. If the kidneys are not functioning properly, the albumin/ creatinine level may be higher than normal.

FAQs

1. When should creatinine level be checked?

Ans. A creatinine test is usually recommended by a doctor usually along with another blood test (BUN) or as part of a comprehensive metabolic panel (CMP).

2. What level of creatinine indicates kidney damage?

Ans. Normal range creatinine may vary with age. Usually, creatinine levels of more than 2.0 in infants and 5.0 in adults may be considered as an indication of kidney damage.

3. What is the cause of high creatinine?

Ans. Creatinine levels can be temporarily high which can be due to taking certain medications, dehydration, or having a protein rich diet. Persistently high levels of creatinine can be a sign of kidney damage.

Reference:
https://www.mayoclinic.org/tests-procedures/creatinine-test/about/pac-20384646
https://www.mountsinai.org/health-library/tests/creatinine-blood-test