Creatinine: what it is, reference values ​​and when to take the test

Creatinine is a substance produced by muscles and eliminated by the kidneys, which serves to produce energy for muscle contraction. Analyzing blood creatinine levels is useful to investigate changes in the kidneys, such as kidney infection or failure, as in these situations creatinine is not eliminated correctly and tends to be higher than normal.

The creatinine test is recommended by the general practitioner or urologist as a routine test or when there are signs and symptoms that may be suggestive of kidney problems, such as excessive tiredness, increased urine volume, swelling and pain in the lower back, for example. Check out the 11 main symptoms of kidney problems.

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

When is indicated

The creatinine test is normally recommended by the general practitioner or urologist to assess 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 lower back, change in urinary frequency. and urine volume. Check out other signs and symptoms of kidney problems.

In most cases, the doctor recommends measuring creatinine in the blood, as 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 that the use of some medications is indicated, as well as it is recommended to suspend the use of cimetidine, aspirin, ibuprofen or cephalosporins, in accordance with medical advice.

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

Creatinine reference values

Blood creatinine reference values ​​vary according to age and gender:

• Newborns: 0,60 a 1,30 mg/dL;
• Babies between 1 and 6 months: 0,40 a 0,60 mg/dL;
• Children and adolescents (1 to 18 years old): 0,4 0 a 0,90 mg/dL;
• Adult women: 0,60 a 1,2 mg/dL;
• Adult men: 0,70 a 1,3 mg/dL.

It is normal for creatinine concentration to vary depending on the amount of muscle mass. For this reason, its concentration in the blood increases in children and decreases in adults, depending on age. Additionally, it is normal for men to have higher normal creatinine levels.

The creatinine reference value may also vary according to the laboratory, depending on the laboratory method used for the analysis. Ideally, the result of the creatinine test should always be evaluated by a doctor.

When to go to the doctor

It is advisable to make an appointment with a nephrologist when creatinine values ​​are above reference values, especially if there are associated symptoms such as tiredness, swelling or changes in urine.

If the nephrologist is not available, you can also consult a general practitioner, who may order other tests to identify the cause.

What can cause high creatinine

High blood creatinine levels may indicate damage to the blood vessels of the kidneys, kidney infection, or reduced blood flow to the kidneys, which may be a consequence of:

• Use of some medications that affect kidney health;
• Feeding with excess protein;
• Presence of kidney stones;
• Chronic diseases, such as high blood pressure or decompensated diabetes.

Furthermore, athletes and bodybuilders may also have high creatinine 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, in which he compares the amount of creatinine obtained in the blood and urine. Therefore, if the problem is in the kidneys, the amount of creatinine in the blood must be higher than the amount in the urine. Find out more about the creatinine clearance test.

How to know creatinine clearance

To find out your creatinine clearance and thus assess your risk of kidney problems, enter the results of your creatinine test into the following calculator:

What can cause low creatinine

Low blood creatinine values ​​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 the production of creatinine. See more about low 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.