Generality
Creatininuria is the amount of creatinine in the urine.
This exam provides useful information on the functional efficiency of the kidneys, as these latter are used to filter blood.
The creatinine dose is often required to measure creatinine clearance and is performed on 24-hour urine collection.
What's this
- Creatinine is the product of the catabolism of creatine phosphate (or phosphocreatine). This molecule is mainly located in skeletal muscle and in the heart. For these tissues, creatinine is an immediately usable source of energy for contraction .
- Creatinine production is related to creatine metabolism. During the absorption of this amino acid by the muscles, a small amount is converted into creatinine in an irreversible and almost constant manner over time.
- Creatinine produced is poured into the blood and is subsequently filtered by the renal glomeruli. The fate of the molecule is to be entirely eliminated in the urine, without being reabsorbed or undergoing significant changes in the renal tubules.
- When renal filtration is normal, the serum creatinine concentration and the amount eliminated in the urine remain constant and are related to muscle mass.
- If the presence of creatinine in the blood is too high, it means that the kidneys cannot pass it into the urine, so they do not do their job well.
- In the presence of a pathological condition that compromises the renal filtration capacity, creatinine is not eliminated properly; the urinary and plasmatic values are affected.
Why do you measure
Since all the creatinine filtered by the glomerulus is completely excreted (there is no resorption), its level in the urine constitutes a sensitive and specific index of renal function. If this is too low it means that the filtering activity of the kidney is compromised and, consequently, there will be an increase in the concentration of creatinine in the blood.
The creatininuria dosage is also performed to monitor the treatment of kidney pathologies (for example, in dialysed patients) or the functionality of the same organs during certain types of therapies.
Normal values
The reference intervals for creatinuria are as follows:
- Normal woman values: 600 - 1800 mg / 24h;
- Normal human values: 800 - 2000 mg / 24h.
However, it must be considered that the amount of creatinine produced by the body depends on age, the development of muscle mass and the physical exercise performed: for this reason, the concentration is slightly higher in men than in women and children.
Creatininuria Alta - Causes
High creatinine in urine can be caused by:
- Temperature
- Fasting
- Muscle hypertrophy
- Diabetes mellitus;
- Acromegaly;
- Enlarged or damaged renal vessels (glomerulonephritis);
- Infections of the kidneys (pyelonephritis);
- Kidney stones;
- Reduced blood supply to the kidneys due to heart failure, atherosclerosis or diabetes complications;
- Prostatic disorders or other causes of obstruction of the urinary tract;
- Muscle hypertrophy;
- Sports excesses;
- Muscle trauma or injury;
- Burns.
An increase in urinary excretion may be associated with medication, such as captopril and corticosteroids.
Low creatinine - Causes
A decrease in urinary creatinine concentration may be due to different situations such as:
- Kidney failure;
- Muscle disorders (eg muscular dystrophy, myositis);
- Anemia;
- States of toxic-septic shock;
- Urinary tract obstruction (prostate adenoma, nephritic colic);
- Acute or chronic glomerulonephritis;
- Polycystic renal disease;
- Hyperthyroidism;
- Old age.
How to measure it
Creatininuria is measured on a sample of urine collected within 24 hours.
Preparation
The exam includes the collection of urine emitted during a whole day (for example: from 8 am to 8 am on the following day), in the same clean plastic container without any additives. Always close the container well and keep it in a cool, dark place.
In the 8-12 hours preceding the creatinine test, it is important to avoid intense physical exercise. In fact, this activity can alter the values.
Furthermore, the patient may be required to remain fasting the night before the withdrawal or to refrain from eating meat.
Interpretation of Results
The increase in creatinine in the urine indicates a deterioration of renal function, acute or chronic, which can be caused by inadequate perfusion (shock, hemorrhage, heart failure), nephropathy (glomerulonephritis, pyelonephritis, acute tubular necrosis, etc.) or obstruction of the urinary tract.
In chronic kidney diseases, accompanied, in particular, by a reduction in muscle mass, creatininuria tends to be reduced. Low levels of creatinine in the urine can also be caused by anemia, muscle atrophy and debilitating states.
It should also be remembered that the results of the analyzes must be evaluated as a whole by the general practitioner, who knows the patient's medical history.
