Creatinine: what é, reference values and when the exam é indicated

Creatinine is a substance present in the blood that is produced by the muscles and eliminated by the kidneys. Thus, the analysis of creatinine levels in the blood can be useful to investigate the presence of any alteration in the kidneys, since in this situation the concentration of this protein would be higher in the blood.

Thus, the creatinine test is indicated by the general practitioner or urologist as a routine exam or when there are signs and symptoms that may be suggestive of renal impairment, such as excessive tiredness, increased urine volume, swelling and pain in the lower back, for example.

In addition to being able to request a blood creatinine test, in some situations, the doctor may recommend evaluating the amount of creatinine released in the urine during the day through a 24-hour urinalysis.

When is indicated

The creatinine test may be recommended by the general practitioner or urologist in order to evaluate the functioning of the kidneys or to investigate the presence of any changes in these organs when there are symptoms such as excessive tiredness, loss of appetite, swelling, pain in the lumbar region, change in urinary frequency and volume of urine. Check out other signs and symptoms of kidney problems.

In most cases, the doctor recommends the measurement of creatinine in the blood, since in the presence of changes in the functioning of the kidneys, there is an increase in the amount of this protein in the blood. In this case, it is important to indicate the use of some medications, as well as suspending the use of cimetidine, aspirin, ibuprofen or cephalosporins, according to medical advice.

In some cases, especially when there are signs indicative of kidney changes, the doctor may indicate the measurement of creatinine in the urine, which is included in the 24-hour urinalysis, in which all the urine produced in the day is collected and analyzed in the laboratory. See 24-hour urine test details.

Exam reference values

Normal reference values for blood creatinine levels may vary by laboratory, depending on the laboratory method used for analysis. Since creatinine is produced in the muscles, its concentration can change as the child develops, so the reference values can also vary according to age:

Newborns: 0.60 to 1.30 mg/dL;
Babies between 1 and 6 months: 0.40 to 0.60 mg/dL;
Children and adolescents (1 to 18 years): 0.4 0 to 0.90 mg/dL.

Also, creatinine levels may vary by gender:

Women: 0.60 to 1.2 mg/dL;
Men: 0.70 to 1.3 mg/dL.

As creatinine is a substance that is produced in the body according to the level of muscle mass, it is normal for men to have higher levels of creatinine in their blood, as they generally have more developed muscles compared to women.

What can cause high creatinine

Increased levels of creatinine in the blood may be indicative of damage to the blood vessels of the kidneys, kidney infection or reduced blood flow to the kidneys, for example, which may be a consequence of the use of medications, diet protein, presence of kidney stones or chronic diseases, such as high blood pressure and decompensated diabetes, for example.

In addition, athletes and bodybuilders can also have high creatinine levels due to intense physical activity, and this increase is not necessarily related to kidney changes. Check out the main causes of high creatinine.

When kidney problems are suspected, the doctor may also order a creatinine clearance test, which compares the amount of creatinine obtained in the blood and urine. Thus, if the problem is in the kidneys, the amount of creatinine in the blood must be greater than the amount in the urine, since the kidneys are not eliminating the substance. Learn more about the creatinine clearance test.

What can cause low creatinine

Low creatinine levels in the blood are not a cause for concern and are more common in pregnant women and patients with liver disease, as the liver is also responsible for producing creatinine.

However, in some people it can also indicate muscle diseases, such as muscular dystrophy, for example, which causes other symptoms such as weakness, muscle pain or difficulty moving the arms or legs.