Creatinine is a waste substance found in the body. It is made by the muscles as a by-product of the breakdown of creatine, which is a compound. Creatinine is removed from the body by the kidneys. Most of it is filtered from the blood and released into the urine to be eliminated from the body. This test is used by the doctor to measure how much creatinine is present in the blood or the urine. The compound creatine is key to the cycle, which makes the energy needed to contract muscles. Creatine and creatinine are produced by the body and present in it in stable amounts. Normally, most of the creatinine is filtered from the blood by the kidneys and removed from the body via excretion, which is why blood composition is a good indicator of how well the kidneys are functioning. The amount of creatinine produced in the body is dependent on the body size and muscle mass which is why levels of creatinine are a little higher in children and women.
The kidneys are a pair of bean-shaped organs that are found at the bottom of the ribcage. Structurally, the kidneys contain millions of tiny blood-filtering units called nephrons. Within the nephrons, the blood is filtered through the glomerulus. The glomerulus allows water and small molecules to pass but prevents the blood cells
and larger molecules from passing out. The tubules attached to the glomerulus collect fluid and molecules which pass through the glomerulus, which reabsorbs what can still be utilized by the body, while the remaining matter is excreted in the urine. The results from this test are used in combination with others, like the 24-hour creatinine test, in order to calculate values that are helpful in assessing how the kidneys are functioning.