Serum Creatinine: What is it? Blood Analysis, Glomerular Filtration Rate and Creatinine Levels

This test is used to evaluate kidney function.

Creatinine is a breakdown product of creatine phosphate in muscle, and it is generally produced at a constant rate by the body (depending on muscle mass).

What is a creatinine blood test?

Measurement of serum creatinine is a simple test, and it is the most commonly used indicator of kidney function. It measures the level of creatinine in your blood and can provide your doctor with information on how well your kidneys are working.

An increase in the level of creatinine in the blood is a late marker, seen only with marked damage to functional nephrons. Therefore, this test is not suitable for detecting early-stage kidney disease.

Each kidney has millions of tiny blood filtering units called nephrons. Nephrons constantly filter blood through a very small group of blood vessels known as glomeruli.

These structures filter waste products, excess water, and other impurities from the blood. The toxins are stored in the bladder and are then eliminated during urination.

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

Creatinine blood tests are usually done in conjunction with other laboratory tests, including a blood urea nitrogen (NUS) test and a basic metabolic panel (PMB) or a complete metabolic panel (PMC).

These tests are done during routine physical exams to help diagnose certain diseases and to detect any problems with your kidney function.

Glomerular filtration rate

A better estimate of kidney function is obtained by calculating the estimated glomerular filtration rate (eGFR).

Estimated glomerular filtration rate can be accurately calculated without a 24-hour urine collection using serum creatinine concentration and some or all of the following variables: gender, age, weight, and race, as suggested by the American Diabetes Association.

Many labs will automatically calculate the estimated glomerular filtration rate when a creatinine test is ordered.

A concern in late 2010 relates to the adoption of a new analytical methodology and a possible impact this may have on clinical medicine.

Most clinical laboratories now align their creatinine measurements with a new standardized isotope dilution mass spectrometry (IDMS) method for measuring serum creatinine.

Isotope dilution mass spectrometry appears to give lower values ​​than older methods when serum creatinine values ​​are relatively low, eg 0.7 mg / dL.

The isotope dilution mass spectrometry method would lead to a comparative overestimation of the corresponding calculated glomerular filtration rate in some patients with normal renal function.

Some drugs are even dosed on normal kidney function at that derived glomerular filtration rate. The dose, unless further modified, could now be higher than desired, which could cause further drug-related toxicity.

To counteract the effect of switching to isotope dilution mass spectrometry, newer food and drug administration guidelines have suggested limiting doses to specific maximums with carboplatin, a chemotherapy drug.

A 2009 Japanese study found that a lower serum creatinine level is associated with an increased risk of developing type 2 diabetes in Japanese men.

Creatinine levels

In general, normal creatinine levels range from 0.9 to 1.3 mg / dL in men and 0.6 to 1.1 mg / dL in women between the ages of 18 and 60. Normal levels are about the same for people over the age of 60.

Elevated levels of serum creatinine in the blood indicate that the kidneys are not working 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 from diabetes.
  • If your creatinine is really high and it comes from acute or chronic kidney injury, the level will not drop until the problem is resolved.

If it was temporarily or falsely elevated due to dehydration, a high protein diet, or the use of supplements, reversing those conditions will lower the level. Also, a person on dialysis will have lower levels after one treatment.

Low creatinine levels are rare, but this can occur as a result of certain conditions that cause a decrease in muscle mass. They are generally not a cause for concern.

It is important to note that normal and abnormal ranges can vary between laboratories because some use single measurements or test different samples.

You should always meet with your doctor to discuss your test results in more detail. They will be able to tell you if more tests are needed and if any treatment will be required.