Creatinine

Why this test?

• To assess kidney function.
• To assess the function of the main organs and systems (in conjunction with other studies).
• To assess kidney function impairment and the effectiveness of its treatment, if creatinine or urea are outside the normal range and the patient has some underlying chronic disease, such as diabetes, the course of which affects the condition of the kidneys.
• If the level of creatinine in the blood and in the urine is known, you can calculate the creatinine clearance (Rehberg's test) - this test shows how efficiently the kidneys filter small molecules such as creatinine from the blood.
• To count GFR to confirm kidney damage.

In what cases is it prescribed?

• After certain periods of time, with already known kidney disease or a disease capable of causing deterioration of kidney function (together with a test for urea and for microalbuminuria).
• When diagnosing skeletal muscle diseases.
• Before and after the hemodialysis procedure.
• With symptoms of kidney dysfunction: weakness, fatigue, decreased attention, poor appetite, sleep problems, swelling on the face, wrists, ankles, ascites, foamy, red or brown urine, decreased diuresis,
• When problems with the urination: burning, intermittent, change in frequency (predominance of nocturnal diuresis), pain in the area of the kidneys (especially on the sides of the spine), under the ribs, high pressure.
• For any pathological conditions accompanied by dehydration.
• When preparing for computed tomography.
• Before prescribing drugs that can cause damage to kidney tissue.

Test information

Creatinine is a residual product found in muscles when creatine is broken down. Creatine enters the cycle that provides the body with energy for muscle contraction. After 7 seconds of intense physical activity, creatine phosphate is converted into creatine, then into creatinine, which is filtered in the kidneys and excreted in the urine. Creatine and creatinine are stably produced by our body in a constant amount. Almost all creatinine is excreted by the kidneys, so its concentration in the blood is a good indicator of their function. The amount of released creatinine depends on total body weight and, in particular, muscle mass. Therefore, for example, creatinine levels in men will be significantly higher than in women and children.

A small part of it (15%) is secreted by the tubules, but mainly it is produced due to filtration in the glomeruli. The level of creatinine in the blood does not go beyond the normal range until glomerular filtration decreases to critical values, especially in patients with low muscle mass. Then the creatinine level rises.

Precisely because of the large number of components (muscle mass, gender, age) that affect the concentration of creatinine in the blood, this study is not the best screening test for detecting kidney failure. At the same time, creatinine is a more sensitive indicator of kidney disease than urea.