Creatinine

It is used to determine whether your kidneys are functioning normally. A calculation based on the serum creatinine concentration, called the eGFR (estimate of glomerular filtration rate) measures how effectively your kidneys are filtering small molecules like creatinine out of your blood. 

Urine creatinine may also be used with a variety of other urine tests as a correction factor. Since it is produced and removed at a relatively constant rate, the amount of creatinine in urine can be compared to the amount of another substance being measured. Examples of this are when creatinine is measured with protein to calculate a urine protein/creatinine ratio (UP/CR) and when it is measured with albumin to calculate microalbumin/creatinine ratio (also known as urine albumin/creatinine ratio, UACR). These tests are used to evaluate kidney function as well as to detect other urinary tract disorders.
 

Creatinine may be part of a routine blood test, widely used when someone has non-specific health complaints, or when your doctor suspects kidney problems. Creatinine and the eGFR are also used to monitor treatment of kidney disease or to monitor kidney function while you are on certain drugs.

Increased creatinine levels in the blood suggest diseases that affect kidney function. These can include:

• glomerulonephritis (swelling of the kidney's blood vessels)
• diabetic kidney disease (the filters clog up with a proteinaceous substance)
• pyelonephritis (pus-forming infection of the kidneys)
• acute kidney injury (death of cells in the kidney's small tubes)
• urinary tract obstruction (e.g. prostate disease or kidney stones)
• reduced blood flow to the kidney due to shock, dehydration, congestive heart failure, atherosclerosis, or complications of diabetes.

Creatinine can also increase as a result of muscle injury. Reduced levels of creatinine are not common and are not usually a cause for concern. As creatinine levels are related to the amount of muscle the person has, low levels may be a consequence of decreased muscle mass (such as in the elderly), but may also be occasionally found in advanced liver disease.

Adult

Male        60-110 µmol/L
Female    45- 90 µmol/L

Paediatrics

0 day to <1 week          22-93 µmol/L
1 week - 4 weeks         17-50 µmol/L
4 weeks - 2 years         11-36 µmol/L
2 years - 6 years           20-44 µmol/L
6 years - 12 years         20-32 µmol/L
Males
12 years -15 years        35–83 µmol/L
15 years - 19 years       50–100 µmol/L
19 years - 60 years       60–110 µmol/L
Females
12 years to 15 years     35–74 µmol/L
15 years to 19 years     38–82 µmol/L
19 years to 60 years     45–90 µmol/L

The reference intervals shown above are known as a harmonised reference interval. This means that eventually all laboratories in Australia will eventually use this same interval so wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted. More information can be found under Reference Intervals – An Overview.

 

Since creatinine levels are in proportion to muscle mass, women tend to have lower levels than men.

In general, creatinine levels will stay the same if you eat a normal diet. However, eating large amounts of meat may cause short-lived increases in blood creatinine levels. Taking creatine supplements may also increase creatinine.

There are a few drugs that interfere with the creatinine test, although there are some drugs that can cause some impairment in kidney function. Your creatinine levels may be monitored if you are taking one of these drugs.

In general, moderate exercise will not affect your creatinine levels. As you continue to exercise and build muscle mass, your creatinine levels may increase slightly, but not to abnormal levels.

In general, creatinine levels will not vary with a normal diet. Creatinine levels may be 10%-30% higher in people who eat a diet that is very high in meat.

Creatine is a compound that is made primarily in the liver and then transported to your muscles where it is used as an energy source for muscle activity. Once in the muscle, some of the creatine is spontaneously converted to creatinine. The amount of both creatine and creatinine depend on muscle mass, so men usually have higher levels than women. Creatine is now available as a dietary supplement. If you take creatine, your creatinine levels may be higher than when you do not take the supplement. You should tell your doctor of all the dietary supplements you are taking to help him/her evaluate your lab results.

Creatinine levels relate to both muscle mass and to kidney function. As you age, your muscle mass decreases but your kidneys tend to function less effectively. The net result is not much change in creatinine levels in the blood as you get older.

Creatinine and urea, together with the eGFR, are the primary tests used to check how well the kidneys filter waste products from your blood. Your doctor may also order electrolyte tests such as sodium and potassium, or calcium to help understand how your kidneys are functioning.

Creatinine levels are generally slightly lower in pregnancy.