Health monitoring of sick kidneys is done by measuring creatinine in the blood and urine. We have discussed these procedures in detail in this article.
Creatinine is a substance that is formed in the body at a constant rate and has a renal excretion pathway. It is therefore a convenient marker for assessing kidney function. The higher the level of creatinine in the biochemical blood test, the worse the kidneys work.
However, it should be taken into account that the rate of creatinine formation depends on muscle mass, which differs in men and women of different ages. Therefore, creatinine norms are different for each person, the “reference values” that are indicated in the forms of laboratories are indicative in nature.
It is more correct to focus on the glomerular filtration rate (GFR) [link to article “Decreased glomerular filtration rate”] rather than the creatinine level itself in assessing kidney function. If creatinine is elevated, there is no doubt that renal function is impaired, but a decrease in the more sensitive creatinine GFR is possible while creatinine is still “normal”.
Normal vs. High Creatinine Levels in Blood
Table of creatinine norms for adults
Creatinine norms in women’s blood are lower than in men. This is due to physiological differences between the female and male bodies:
- women have a smaller volume of muscle tissue;
- Women experience less physical activity;
- metabolism is slower;
- Creatinine levels are suppressed by female sex hormones.
Blood creatinine levels in women during pregnancy are even lower, as energy expenditure increases due to the growth of the fetus.
The table shows creatinine norms in adults:
| Age and gender | Normal, μmol/l |
|---|---|
| Women 18-50 yo | 53-97 |
| Women over 50 | 53-106 |
| Men 18-50 yo | 80-150 |
| Men over 50 | 70-115 |
Separately, it is worth mentioning the creatinine rate for a single kidney. Since the kidneys are paired organs, when one of them is removed, the second takes on an additional function, increasing in size. The first time after the removal of one kidney there is hypercreatininemia. Then, when the second kidney starts working harder, creatinine decreases and reaches the upper limit of normal for a healthy person.
Table of creatinine norms for children
Creatinine norms in children vary by age. Its highest amount is observed during the period of active growth of the child, when the volume of muscle mass increases several times. By adolescence the amount becomes the same as in adults.
| Age | Normal, μmol/l |
|---|---|
| 1-30 days | 19-78 |
| Up to 3 yo | 20-37 |
| Up to 5 yo | 25-45 |
| Up to 10 yo | 34-57 |
An increased creatinine level on the biochemical blood test is an indication for consultation with a nephrologist.
Creatinine increases strength, muscle mass and athletic performance. Creatine is at the beginning of the chain of conversions. This ingredient has a long journey through the body, starting in the kidneys and continuing in the liver. After this, the substance is sent to the muscles where creatine is converted into creatine phosphate. The resulting component goes to the muscles, giving them the energy to contract. After its use, the residue follows into the bloodstream and is excreted with the urine. This energy turnover occurs constantly in the body; the amount of the substance in the blood system remains the same, provided the body is in a normal state.
Causes
Professional athletes and those whose work involves heavy physical exertion, as well as people on a diet or taking some antibacterial drugs have a slight increase in creatinine in the blood. These are physiological reasons, they do not manifest themselves clinically and do not require special correction. Pathologically elevated creatinine level is usually accompanied by the appearance of symptoms such as pulling pains in the lower back, unmotivated weakness, fatigue, drowsiness, impaired consciousness. This symptomology may be associated with both an increase in creatinine intake from the muscle and an impairment of creatinine excretion.
A significant increase in creatinine levels occurs in acute and chronic renal failure. Along with renal problems, high levels are observed in severe heart failure, thyroid dysfunction, as well as in some malignant tumors that cause muscle tissue decay. The same effect is caused by trauma with muscle damage, burns, prolonged compression syndrome, radiation sickness.
This figure depends entirely on gender and age, as well as kidney function, accumulated muscle mass, and food preferences.
If the blood creatinine level is slightly above the norm, and the person tested has an athletic build and does not belong to people who eat only plant-based foods, then there is no reason to worry.
If they are elderly people, the creatinine level is lowered, therefore, the results of the analysis simply state age-related changes in the body.
Creatinine Levels in Blood According to Gender
Let’s pay attention to the fact that the norm of creatinine is different in men and women. This can be explained by the fact that the stronger half is endowed with more muscle mass. A small deviation of creatinine from the norm may not be considered as a problem, as the person is in constant energy exchange and the excess energy can be used in the next moment. But if the creatinine level is seriously exceeded, it means that for some reason there were problems with the excretion of the substance, which led to the accumulation of creatinine in the blood and toxic effects on the body.
Urinary Creatinine Level
The end product of the breakdown of creatine and creatine phosphate, which is excreted by the kidneys and used in the evaluation of their excretory and filtration function.
- Name of the test: Creatinine (Creat; Cre), 24-Hour Urine, Urine creatinine.
- Test method: Kinetic method (Jaffe method).
- Units of Measurement: Mmol/day. (millimoles per day).
- What biomaterial can be used for the study? Daily urine.
How to properly prepare for the test?
- Eliminate alcohol from your diet 24 hours before the test.
- Do not eat spicy, salty food, foods that change the color of urine (eg, beets, carrots) for 12 hours before the study.
- Do not take diuretics for 48 hours before the collection of urine (by agreement with the doctor).
- Exclude physical and emotional stress at the time of collecting daily urine (during the day).
What is it?
Creatinine is the end product of the breakdown of creatine and creatine phosphate mainly in muscle tissue. Creatine and creatine phosphate are involved in biochemical conversion processes with the release of energy required for muscle fiber contraction. All creatinine is excreted by the kidneys at a relatively constant rate. It is almost never reabsorbed from the urine back into the blood, so its level in the urine allows an assessment of the filtration capacity of the kidneys. The concentration of creatinine in the urine is several tens or hundreds of times higher than in the blood.
Daily urinary creatinine excretion is relatively constant and proportional to daily creatinine production. The amount of creatinine formed depends on muscle mass, sex, and age, so it is greater in men than in women and children.
By simultaneously determining the concentration of creatinine in the blood and daily urine, creatinine clearance – the rate at which the blood is cleared of this substance per unit time – is calculated. It characterizes the rate of glomerular filtration in the kidneys. Normally, when creatinine in the blood increases, its filtration in the kidneys also increases. Renal disorders prevent creatinine from being excreted in the urine.
If creatinine level is determined only in blood, diagnostically significant changes will be detected only if more than half of renal nephrons are dead, and additional analysis of daily urine creatinine will allow to detect pathology at an earlier stage.
Blood and urine creatinine testing is included in most renal function panels and is prescribed in conjunction with determination of other biochemical components of urine.
Because the daily creatinine excretion is relatively stable, this test can be used to determine if the daily urine collection is properly performed for other diagnostic purposes.
Creatinine and urine protein or creatinine and albumin tests are also used simultaneously in the diagnosis of various kidney disorders.
Normal Results of Urine Creatinine Test
| Gender | Reference values |
| Woman | 5,3 – 15,9 mmol/day. |
| Man | 7,1 – 17,7 mmol/day. |
What is the test used for?
- To assess the functional state of the kidneys.
- To dynamically monitor patients with kidney pathology.
- To assess the correctness of the collection of daily urine for other laboratory tests.
When is the test appointed?
- When preventive examination of a patient.
- When kidney pathology is suspected and with symptoms of renal dysfunction (swelling in the face, around the eyes, swelling of the shins, ankles, changes in the properties of urine, pain in the lumbar region, disorders of urination).
- If the patient has acute or chronic diseases that are often accompanied by kidney damage (arterial hypertension, diabetes mellitus, systemic lupus erythematosus, vasculitis).
- When monitoring the treatment of patients with kidney disease.
- In the study of levels of hormones and other biological substances in daily urine.
Causes of increased creatinine levels in daily urine:
- Acromegaly and gigantism (increased production of growth hormone);
- diabetes mellitus;
- hypothyroidism;
- excessive consumption of animal proteins in the diet;
- physical exertion;
- acute infections;
- prolonged tissue compression syndrome (crush syndrome);
- burns.
Causes of decreased creatinine levels in daily urine:
- Advanced renal disease;
- renal amyloidosis;
- hyperthyroidism;
- anemia;
- muscular dystrophy;
- polymyositis, neurogenic atrophy;
- inflammatory muscle diseases (myositis);
- renal artery stenosis;
- leukemia;
- radiation sickness;
- vegetarian diet.
What can affect the result?
- Incorrect collection and storage of material can lead to distorted results.
- Creatinine clearance increases after physical exertion and during pregnancy and its concentration in the urine increases.
- Excessive consumption of meat products increases the amount of creatinine in the blood and urine.
- Drugs that increase urinary creatinine levels: ascorbic acid, corticosteroids, methyldopa, methotrexate, nandrolone, nitrofurantoin, nitrofurazon, oxymetholone, prednisolone, fluoxymesterone, cefazolin, cephalothin, cefoxitin.
- Drugs that lower urinary creatinine: anabolic steroids, captopril, quinapril, ketoprofen, thiazide diuretics.
What else you should know
Reverse reabsorption of creatinine from the urine into the blood is possible when diuresis (volume of urine excreted) is drastically reduced. This occurs in severe congestive heart failure, uncontrolled diabetes mellitus or acute renal failure.
It is also recommended that:
- Serum creatinine
- Serum urea
- Urea in daily urine
- Uric acid in daily urine
- Calcium in daily urine
- Potassium, sodium, chlorine in daily urine
- Total urine protein
- Total serum protein
- Albumin in the urine (microalbuminuria)
- Rehberg test (endogenous creatinine clearance)
- Urinalysis with microscopy
Who prescribes the test?
Therapist, nephrologist, urologist, general practitioner.
