Creatinine

Creatinine is a nitrogen-containing waste product formed mainly by the spontaneous breakdown of creatine and phosphocreatine in muscle. The kidneys clear it from blood, making its concentration useful for assessing kidney function.

Creatine: Creatine is a compound that helps supply energy to muscle and other tissues. Creatinine forms as creatine and its phosphorylated form break down.
Estimated glomerular filtration rate: Estimated glomerular filtration rate is a calculated measure of kidney filtration based on blood markers and personal characteristics. Creatinine is the marker most commonly used to calculate this estimate.
Blood urea nitrogen: Blood urea nitrogen measures the concentration of nitrogen in blood carried as urea. Like creatinine, it reflects kidney function, but diet and fluid status affect it more strongly.
Kidney: A kidney is an organ that filters blood, regulates fluid and electrolytes, and produces urine. Creatinine concentration reflects how effectively these organs remove it.
Phosphocreatine: Phosphocreatine is an energy-storage molecule that rapidly donates phosphate to regenerate ATP in cells. Its breakdown contributes to the steady production of creatinine.
Serum creatinine: Serum creatinine is the concentration of creatinine in the liquid portion of blood. This routine test is the usual input for creatinine-based kidney estimates.
Creatine kinase: Creatine kinase is an enzyme that catalyzes phosphate transfer involving creatine and phosphocreatine. It is a muscle-injury marker, unlike creatinine, which is a metabolic waste product.
Nephron: A nephron is the kidney’s functional unit, containing a filter and a tubule that processes filtrate. Filtration and secretion of creatinine occur across nephron structures.
Glomerular filtration: Glomerular filtration is the movement of water and small solutes from blood into kidney nephrons. It is the main route by which kidneys remove creatinine from blood.
Acute kidney injury: Acute kidney injury is a rapid decline in kidney function over hours or days. A rising blood creatinine concentration is a standard indicator of this condition.

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