Serum creatinine - what is it and what are its normal levels?

Blood counts are one of the basic tests that can alert you to the presence of various pathophysiological conditions in your body. They are relatively cheap and can be invaluable in the diagnosis of various diseases. In this article let us focus on creatinine levels in the blood serum, which reflects the state of the kidneys' excretory function.

What exactly is creatinine? 

Creatinine is an organic chemical compound - a derivative of creatine, one of the most important nitrogen compounds in the blood. It is produced during the metabolism of proteins (creatine) in the human body, mainly in skeletal muscles. It is excreted by the kidneys with urine alongside urea (consisting mainly of nitrogen compounds).  

Creatinine level tests 

Blood creatinine levels are measured with a biochemical test that gauges the kidneys' ability to excrete unwanted compounds. The test result determines how much creatinine is excreted from the human body over 24 hours. Thus, it assesses the degree to which a person's kidneys are able to properly cleanse the blood of toxic substances that are created during metabolism.

The amount of excreted creatinine depends, among others, on a person’s:

muscle mass,

age,

gender,

general health,

diet.

Creatinine test - indications 

The indication for this kind of test is the need for renal function assessment, which is performed, among others: 

before many surgical procedures,

when kidney, liver, or pancreas failure is suspected,

before diagnostic tests requiring the administration of a contrast agent (computed tomography, magnetic resonance imaging, coronary catheterization).  

Creatinine testing is also important in patients undergoing dialysis or after kidney transplantation.  

Creatinine is usually measured in the blood serum.  

In some cases, it is necessary to determine its daily excretion in the urine. The result is then used to calculate the creatinine clearance. It is usually reported using the GFR or glomerular filtration rate. It is the most important factor in measuring the functioning of kidneys and is calculated based on the creatinine test results.  

Creatinine test - preparing for the test  

The test does not require any extensive preparation.  

However, remember that the test should be performed on an empty stomach (after about 8-10 hours without a meal) - done that way it will be the most reliable.  

The test should be performed in the morning and before having it performed you should drink a glass of water. This helps reduce the result's distortion, as in some cases creatinine can be unreasonably elevated. The results may also be affected by intense physical activity, so you should limit physical activity a day before the test.  

Normal creatinine levels in the blood serum 

The test result for an adult should range from 53 to 115 mmol/l, i.e. 0.6-1.3 mg/dl, and the GFR ³ should equal about 90 ml/min/1.73m2. In newborns, the creatinine level norm ranges between 0.3 and 1.0 mg/dl, in infants about 0.2-0.4 mg/dl, while in older children 0.3-0.7 mg/dl.  

Elevated creatinine levels 

Elevated creatinine levels may suggest worsening renal function. Sometimes even acute. In these cases, the creatinine level rises rapidly. In the event of chronic renal failure, the abnormal test results may persist for more than 3 months. Elevated creatinine levels are also observed in people with cardiac insufficiency, multi-organ failure, or in shock.

Lowered creatinine levels 

Lowered creatinine levels occur in those: 

with low muscle mass,

malnourished,

running a drastic diet,

suffering from diseases leading to muscle loss and liver diseases,

in pregnant women.  

Too low creatinine levels may also appear in people taking anti-inflammatory drugs, steroids, and diuretics. 

Low creatinine level should not be worrying if you do not suffer from the aforementioned diseases. However, elevated creatinine levels can be dangerous to health. If you do not suffer from heart failure or multi-organ failure, and the test result is still elevated, you can try to relieve the kidneys by changing your diet. Try giving up high-protein products in favor of fats and carbohydrates. Fats should be mainly of vegetable origin, while carbohydrates should be complex.