Creatinine is a waste chemical produced in the muscles during the metabolism of phosphocreatine, a protein essential for the production of the energy necessary for muscle activity.
Once produced, creatinine is filtered by the kidneys and excreted from the body via the urine. If the kidneys are not functioning properly, the amount of creatinine in the blood increases because it is not eliminated. This is why the level of creatinine in the urine is an indicator reliable to understand if the kidneys are functioning well or if there is kidney dysfunction.
The amount of creatinine produced by an individual depends on gender, weight or age and is proportional to their muscle mass. Men, in fact, have higher levels of creatinine than women and children. Even the intake of some supplements food based on creatine can increase the quantities in the body. It is therefore advisable to always inform the treating physician of their use in order to allow him to evaluate and correctly interpret the results of the analyzes carried out.
The detection of creatinine values (tests) is essential to evaluate renal function. It is prescribed for people who have ailments (symptoms) such as:
- fatigue, problems concentrating, poor appetite, sleep disturbances
- swelling, especially around the eyes, face, wrists, abdomen, thighs or ankles
- dark urine, with traces of blood or coffee color
- decrease in the amount of urine
- difficulty urinating, burning, abnormal discharge, change in the frequency of urinating especially at night
- flank pain under the ribs, in the kidney area
- high pressure
The creatinine test is also required at regular intervals to those who suffer from kidney disease, both to keep the progression of the disease under control and to ascertain the "effectiveness of" any drug treatment (therapy). In particular, the examination is recommended once a year for people suffering from diseases that can affect the kidneys such as: type 1 diabetes, type 2 diabetes and hypertension.
Even in the absence of specific disorders, the test can still be ordered to check the correct functioning of the kidneys. It can be done in the blood and urine.
In the first case, the exam, called creatininemia, is performed on blood drawn with a needle from a vein in the arm. The person who undergoes it must be fasting and must not have made any physical effort in the 8-12 hours prior to the collection. You will be able to return to your activities immediately afterwards. The blood creatinine test alone is not, however, able to accurately estimate renal function, therefore, it is often associated with the search for the amount of creatinine in the urine through an "analysis called creatininuria. To perform it you need a urine sample collected in 24 hours according to a very precise method: after having thrown away the first urine of the morning, all that produced during the day and the first one of the following morning must be collected in special containers purchased at the pharmacy (the recommended capacity is 2.5 liters and it is good that it has a convenient screw cap). Urine should be stored in the refrigerator between 4 ° -8 ° C in order to limit the growth of germs and the direct action of light.Taking medications does not affect the results of these tests, but it is always advisable to tell your doctor if you are taking any medications for the aforementioned diseases (eg, diuretics).
The results of the blood test and the urine test can also be used for a third, even more thorough examination: the creatinine clearance (i.e. purified creatinine). It is a combined test that correlates the results of creatinine measurements in blood and urine. The normal value of creatinine clearance is between 95 and 140 milliliters per minute (ml / minute) in men and between 85 and 130 ml / minute in women. If the result is lower than normal, it is possible to suspect kidney failure and other follow-up tests may be required. If the result is higher than normal, it is probably simply a person with low muscle mass. For this analysis it is very important to be fasting and resting from physical exertion. at least 8-12 hours prior to collection.
Lately, in adults (over 18 years of age), together with creatinine, most laboratories carry out a further control test to discover early damage to the kidneys and to evaluate their functionality over time. This is the GFR (glomerular filtration rate) which can be determined, without the use of other tests, at the same time as the blood sample is taken for creatinine measurement. No special preparation is required except to avoid eating meat in the 12 hours preceding the exam.
The result of the analysis should normally have a value between 90 and 120 ml / min and in any case not less than 60 ml / min / BSA (body surface area).
It is important to remember that, even in this case, the result obtained depends on variable factors such as: age, sex, muscle mass, weight etc.
The creatinine values present in the blood and urine vary according to the age, sex, weight and height of the person undergoing the analysis.
Normal blood creatinine can range from 0.84 to 1.21 milligrams per deciliter (mg / dL). Men usually have higher levels than women because the amount of creatinine in the blood increases with the size of the muscle mass. It should be noted that the values identified as normal (reference values) in the test results can vary from one laboratory to another and are generally reported next to the values detected by the test.
Quantities higher than those identified as normal (reference values) indicate that creatinine is high. Muscular people can have higher levels of creatinine in their blood than normal without them indicating the presence of disease. The elderly, on the other hand, may have lower values than the norm. Newborns have creatinine levels that hover around 0.2 mg / dL or more, depending on their muscle development.
Normal urinary creatinine values are 0.8 g per 24 hours and depend on muscle mass.
Any condition that impairs kidney function can increase the level of creatinine in the blood. Therefore, if there is an increase in blood creatinine above the average values indicated, the reason must be ascertained (diagnosed). In particular, first of all, it is necessary to understand whether the cause is renal failure and, if so, whether it has been present for some time or has recently occurred. High blood pressure and diabetes mellitus can also lead to an elevated creatinine level (hypercreatininemia).In this case, the kidneys may not do their job well and may not "pass" the creatinine present in the blood into the urine. The doctor will probably offer to perform another test to confirm, or not, the result. In fact, if kidney damage is suspected, it is important to eliminate all factors that could aggravate it since the alterations in the functioning of the kidneys are permanent and irreversible. Proper treatment, on the other hand, can help keep their condition from worsening.
Temporary increases in the level of creatinine in the blood can also occur as a result of a diet rich in protein (eating too much meat), sports excesses, muscle damage (trauma), excessive production of thyroid hormones (hyperthyroidism), deficiency of water in the body (dehydration) or for taking certain drugs such as those used in oncology, cardiology, gastroenterology or anti-infectives.
Some antibiotics also alter creatinine levels in the blood: aminoglycosides, for example, can increase it and cause kidney damage, while cephalosporins increase its levels in the blood without causing any kidney damage. Considering the variability of the factors that can influence creatinine levels, before drawing hasty conclusions on the evaluation of the results of your analyzes it is advisable to submit them to your doctor and inform him of your habits and of the possible use of concomitant drugs with the measurement of creatinine. the attending physician who knows his clients and the evolution of their state of health over time will be able to indicate any other tests to be performed and / or the most appropriate treatments.
The most common disorders related to high creatinine in the blood are: dehydration, fatigue, frequent tiredness, swelling in the feet, ankles or around the eyes, poor appetite, itching and dry skin, muscle cramps, frequent urination and painful sensation, lack of breathlessness, confusional state.
Low creatinine levels (hypocreatininemia) are not common and are usually not a cause for concern. A slight decrease in creatinine is commonly seen during pregnancy, when the fetus begins to develop in the womb and nutrients are transported from the mother to the baby via the umbilical cord. Other causes of low blood creatinine are: decreased muscle mass following normal aging, muscle disease, liver disease, a low protein (low meat) diet.
In the event that the analyzes show high creatinine values, it may be useful to follow some tips such as:
- drink plenty of water (about 2 liters), to hydrate properly throughout the day and to allow the kidneys to function at their best
- avoid the intake of refined sugars, drinks with caffeine and alcohol, which increase body dehydration and strain the kidneys
- moderate the consumption of protein (especially animal) in the diet, such as red meat and cheeses as an excess of them would strain the kidneys
- reduce the consumption of salt
- increase the consumption of fruits, vegetables, seeds and whole grains, which provide fiber and help intestinal balance
- be very rested
- try to limit physical efforts and intense physical activity, since, being creatinine produced by muscle metabolism, the more the muscles work, the higher will be its levels in the blood
Humanitas Research Hospital. Creatinine (Creatininemia)
Bambino Gesù Pediatric Hospital. Creatinine
Niguarda Hospital.Laboratory tests. Creatinine
Mayo Clinc. Creatinine tests (English)
MedlinePlus. Creatinine test (English)
Corriere della Sera. Health. Blood tests. Creatininemia