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Creatinine is a waste product made by the body during regular metabolism. It is excreted into the urine by the kidneys. A serum creatinine test measures the level of creatinine in the blood.
The level of creatinine in the blood is a good measure of overall kidney function.
When the kidneys are not working properly for any reason, they are not able to excrete creatinine into the urine. When this happens, the level of creatinine in the blood rises.

The normal level of creatinine varies slightly based on age, body size, and sex. The level also changes during pregnancy.
However, the normal level is usually between 0.5 and 1.4 milligrams per deciliter (mg/dl).

It is increased in acute or chronic renal failure; urinary tract obstruction, nephrotoxic drugs.
It is decreased in reduced muscle mass, possible drug effect.
This test is ordered for different reasons. For example, healthcare providers may order this test when they think a person is dehydrated or has kidney damage.
This test may also be ordered before or after a provider prescribes certain medications.
The main reason to order the test is to make sure the kidneys are working properly
. To perform a serum creatinine test, a blood sample is taken from a vein on the forearm or hand.

A positive test means - An elevated value for this test can occur in many different situations, including:
- decreased blood flow to the kidneys. This can occur with severe dehydration, massive blood loss, or congestive heart failure. Blockage in the kidney arteries, called renal artery stenosis, can also cause an elevated value on this test.
- kidney damage or failure, which may be due to high blood pressure or diabetes. An inherited condition called polycystic kidney disease can also damage the kidneys. Damage to the kidneys can also occur when the blood calcium level is too high, called hypercalcemia. A cancer called multiple myeloma is another cause. Autoimmune diseases , conditions in which a person's immune system attacks his or her own body, can also cause kidney damage.
- blockage of urine flow, which commonly occurs with enlargement of the prostate, also called benign prostatic hyperplasia
- taking certain medications, such as captopril or non-steroidal anti-inflammatory drugs, or NSAIDs

A negative test means - Normal levels mean that kidney function is normal, but do not mean that everything about the kidney is normal.