Creatinine is produced at a constant rate depending on body and muscle mass. Therefore, the blood level is higher in men than in women and children. Since the kidneys are the main excretion route, it is the most used analysis parameter in the evaluation of the filtration function of the kidneys.

What is creatine?

Creatine is used in our body as part of energy production systems. People who need more energy and lean muscle, those who work in jobs that require intense physical activity, those who are exposed to physical stress and long-term fatigue need creatine more.

Creatine, which is produced by the breakdown of amino acids such as glycine, arginine and methionine in our body, is an amino acid derivative synthesized in the liver, kidneys and pancreas. Once formed, it is transported to the skeletal muscles, heart, brain, and other tissues. In order to meet the sudden energy needs in these tissues, it helps to break down ATP and turns into ‘ creatine phosphate (phosphocreatine)’, which is the energy storage form.

What is creatinine?

Creatine phosphate is broken down into creatinine . In other words, creatinine is one of the products that emerge after the various amino acids that are initially found as creatine are broken down in later stages.

Creatinine is produced at a constant rate depending on body and muscle mass. Therefore, the blood level is higher in men than in women and children. Since the kidneys are the main excretion route, it is the most used analysis parameter in the evaluation of the filtration function of the kidneys.

It is not a very sensitive test in the early stages of kidney function loss. In cases where renal dysfunction is suspected, besides measuring serum creatinine concentration, creatinine clearance should also be determined.

The creatinine molecule is the end product of the molecule whose main ingredient is creatine. Creatinine is measured in two different ways:

  • Measurement of creatinine in the bloodstream
  • In the urine, creatinine clearance (24-hour urine test)

The creatinine value is mostly used in the monitoring of kidney disorders and kidney functions. However, in conditions such as chronic renal failure and loss of kidney function, serum creatinine measurement may not provide sufficiently sensitive information. Urine creatinine clearance may need to be evaluated in such cases.

Kidneys regulate blood pressure, balance body pH and blood electrolyte level. It also filters the body wastes created by the metabolism and released into the bloodstream, allowing them to be disposed of. Useful substances are released back into the bloodstream, while many useless organic waste materials are excreted through the urine.

On average, 180 liters of blood are filtered from the kidneys per day, and 99% of this is reabsorbed. Only 1-2 liters of water and organic waste are thrown out of the body with urine. The three most important organic substances excreted from the body are uric acid, urea and creatinine.

Creatine is an organic waste formed by the metabolism formed by the work of the muscles. However, since creatinine is constantly produced, a certain amount of creatinine is constantly present in the human body.

Normal creatinine values in the blood:

Normal value of serum creatinine for adults:

  • 50 mg/dL to 1.40 mg/dL in men
  • 50 mg/dL to 1.30 mg/dL in women

Normal creatinine clearance values in urine (24 hour urine):

  • 13-50 years:
  • 90-137 mL/min in men.
  • 80-125 mL/min in women.
  • 51-60 years old:
  • 85-132 mL/min in men.
  • 75-120 mL/min in women.
  • 60 years and older:
  • 80-132 mL/min in men.
  • 70-120 mL/min in women.

The level of creatinine in the blood can vary according to many factors. However, it is a protein whose blood level is very well controlled in healthy individuals. It is slightly more common in men than in women. It has higher average values in black race than white race. It can also be affected by a vegetarian diet or diets containing cooked meat. Differences can be seen between individuals with strong musculature and individuals with amputation or malnutrition. Serum levels may change with some drugs, especially active substances such as cimetidine, trimethoprim, cephalosporins. In addition, changes may occur depending on pregnancy or measurement method differences.

Drugs that affect blood creatinine or urinary creatinine clearance:

Some of the drugs cause damage to the kidney cells, reducing the urinary excretion of creatinine and causing an increase in the blood level. Some drugs can affect creatinine levels by disrupting renal hemodynamics or causing dehydration by excessive fluid excretion. Some drugs affect creatinine analysis methods, while others directly affect creatinine production, distribution, or renal excretion. Some of these drugs are:

  • Aminoglycosides
  • Cisplatin
  • Cyclosporine
  • Cephalosporin
  • Methyldopa
  • Phenasemide
  • Furosemide
  • Flucytosine
  • Lidocaine
  • Cimetidine
  • Trimethoprim
  • Primethamine
  • Salicylate

When evaluating creatinine levels, it is usually not evaluated alone. Renal function tests are evaluated together with serum albumin or urine albumin levels, blood urea level, or many other test results specific to the patient’s clinic.

Even in people whose kidney filtration rate is reduced by half, serum creatinine levels can be seen at normal levels. Therefore, serum creatinine levels alone may not be sufficient to evaluate renal function.

The blood creatinine level is checked in those with known chronic kidney disease, in cases that cause narrowing of the urinary tract (stones, etc.), in those who have chronic kidney disease in their relatives, in those who use nephrotoxic drugs, in those with systemic diseases that may affect the kidneys or in people at risk for kidney diseases.

Possible causes of acute creatinine elevation:

Possible causes in patients whose creatinine levels increased by 0.3 mg/dl within a week, although they were previously normal:

  • Sudden onset of fever or hypertension
  • Sudden decrease in urine output
  • Hypovolemia
  • Sepsis
  • Hypertension attacks
  • Recent use of potential nephrotoxic agents

Possible chronic causes of high creatinine levels:

  • Chronic kidney disease
  • Anemia
  • Atrophic kidney
  • Hypocalcemia
  • Hyperphosphatemia
  • Diabetes
  • Autoimmune disorders such as Systemic Lupus Erythematosus
  • Goodpasture syndrome
  • Gout
  • Rhabdomyolysis
  • Muscular dystrophy

If the creatinine level is detected in two intermittent measurements, renal filtration rates are also checked in these patients. If the renal filtration rate is below 60 ml/min, detailed nephrological evaluation is required.

If the renal filtration rate is above 60 ml/min, the creatinine level is monitored. If the creatinine level continues to increase, a nephrological evaluation is performed. If the creatinine level is stable, blood or protein levels are monitored in the urine. If blood or protein is present in the urine, nephrological evaluation is required.

In any case, children with high creatinine levels should be evaluated by a nephrologist or pediatrician. Because a creatinine level of 1mg/dl in a child under 5 years old indicates a GFR decrease of at least around 70%. Growth retardation may begin in children with a GFR below 70 ml/min.

Causes of low creatinine:

  • Senile
  • Weight loss
  • Myasthenia gravis
  • Duchenne muscular dystrophy (DMD)
  • Fluid loss during pregnancy
  • Diet poor in protein
  • Infections
  • Blockages in the bladder and urinary tract
  • Decreased blood flow to the kidneys
  • Heart failure
  • Damage to the kidneys
  • Kidney failure
  • Kidney cancer