Serum creatinine: what is this blood creatinine test used for?

Definition: what is creatinine?

Creatinine is the product of creatine degradation, an amino acid produced by the liver and used by the muscles. This organic waste then passes into the blood and is eliminated by the kidneys through the urinary tract.

Dr. Inès Dominique, urologist: The creatinine level is used to check kidney function, it is said to be a marker of kidney function.

Serum creatinine: blood test to measure creatine levels

The creatinine dosage present in the blood is carried out using a blood sample and is called serum creatinine. “It is a routine examination which is – among other things – offered as part of complete health check-ups”, indicates the specialist. The sample is generally taken from the bend of the elbow. It is recommended, the day before the examination, not to practice intense physical exercise, to avoid consuming red meat (very rich in creatine) and to avoid products – drinks or food – diuretics.

The level of creatinine in the blood depends on several parametersincluding mainly muscle mass: “the more muscular you are, the more creatine you degrade and therefore the higher the amount of creatinine in the blood”, explains the urologist, which makes it difficult to interpret this figure.

To assess renal function more reliably, we calculate, from the serum creatinine level, the GFR (DFG) also called serum creatinine clearance.

What is serum creatinine assay with clearance calculation?

The serum creatinine clearance or GFR is considered as the most accurate parameter to assess kidney function. It corresponds to the volume of plasma filtered by the kidneys per unit of time and is correlated with the functional nephrotic mass.

The GFR is calculated using a mathematical formula including – in addition to serum creatinine – parameters specific to each person: age, sex, weight, ethnicity, etc.
Several GFR calculation methods exist, but the three most frequently used are:

• simplified MDRD formula (2006),
• formula CKD-EPI (2009),
• formula of Cockcroft and Gault (1976), less and less used.

What is the creatinine test used for? Video answer

Norms: what are the normal creatinine values?

Normal blood creatinine values ​​therefore depend on many factors, mainly muscle mass and gender. Overall, the standards are considered to be around:

• 5 to 10 mg/L for a femme
• 6.5 to 12 mg/L for a homme.

But it is the calculation of the clearance which will give the most precise indications on the functioning of the kidneys. And remember that the higher the creatinine, the lower the clearance :

• a GFR of less than 90 ml/min/1, m73² is considered normal;
• a GFR of between 60 and 90 ml/min/1, m73² is the sign of slightly too high serum creatinine, which requires additional examinations;
• below 60 ml/min/1, m73², the GFR is too low: it is considered that there is a chronic kidney disease (CRD).

Low creatinine: what causes?

He is very rare that serum creatinine is too low. “This can happen when the muscle mass is abnormally low, in the case of muscular dystrophy for example or in people in wheelchairs”, indicates Dr. Dominique. Liver damage can also lower blood creatinine levels. Finally, elderly people suffering from muscle wasting as well as pregnant women may also have low serum creatinine.

High creatinine: what causes serum creatinine to rise?

A rise in serum creatinine is a sign of impaired kidney functionwhich can have a number of causes:

• the dehydration,
• an infection,
• kidney stones,
• chronic kidney disease,
• high blood pressure,
• and diabetes or pre-diabetes,
• heart failure,
• rhabdomyolysis,
• tobacco is recognized as a factor in the aggravation of kidney disease,
• physical exhaustion,
• a very protein-rich diet.

What level of creatinine is dangerous?

More than the creatinine level, it is the clearance calculation, or GFR, which is monitored and must alert.

Between 15 and 30 ml/min/1, m73²kidney failure is considered to be severe,

Dr. Dominique: Below 15 ml/min/1.m73² we speak of end-stage renal failure: a kidney transplant or dialysis must then be considered to supplement the kidneys.

How to lower the level of creatinine in the blood?

To lower blood creatinine levels, the kidneys must be protected.

• Stay well hydrated: by drinking at least 1.5 liters of water a day.
• Balance Diabetes.
• Identify the treatable cause of the increase in creatinine and treat it: “this can be by removing a stone or by treating an infection for example”, explains Dr. Dominique.
• Treat hypertension.
• Treat any cardiac pathologies.
• Stop nephrotoxic drugs.
• Avoid eating too much salt: it is recommended not to consume more than 6 g of salt per day ideally.
• Stop smoking.
• Limit animal protein intake to one serving of meat/fish or eggs per day.