serum creatinine

Creatinine is a waste product made steadily as muscles use energy, and the kidneys filter it out into the urine. Because the body produces it at a fairly constant rate, the amount left in the blood is a convenient gauge of how well the kidneys are clearing waste.

When kidney filtering slows, creatinine backs up in the blood and the level rises. From this value, clinicians estimate the glomerular filtration rate, a measure of overall kidney function. Heart and kidney health are tightly linked: heart failure can starve the kidneys of blood flow, and poor kidney function worsens heart outcomes.

Creatinine matters intensely in cardiology because the kidneys clear many heart medications, and impaired function changes how drugs like certain anticoagulants and digoxin are dosed. It also flags risk from contrast dye used in angiography. As a marker, it lags behind real-time kidney changes and is influenced by muscle mass, so it is interpreted alongside other tests.