Creatinine is a waste product of muscle energy metabolism that is cleared from the blood almost entirely by the kidneys. Its concentration in serum therefore serves as a routine indicator of how well the kidneys are filtering. Because production depends on muscle mass, the same value carries a different weight in a large muscular body than in a small or frail one.
No readings for this marker yet.
Raised creatinine most often points at reduced filtration, whether from dehydration, an acute kidney injury, or longer-standing kidney disease; drugs that reduce renal blood flow, such as anti-inflammatories, can push it up as well. Lowered values are less telling and are most often seen with low muscle mass, prolonged immobility, or pregnancy. A single value outside the range is a reason to repeat the test and discuss it with a doctor, not a conclusion about kidney health.
A large meat meal, strenuous exercise in the preceding day, creatine supplements, and dehydration all shift the result, so blood is usually drawn rested and reasonably hydrated. Some medications block creatinine secretion in the tubules without changing true filtration, raising the number harmlessly. It is read alongside eGFR, which is calculated from it, and with urea and cystatin C, which help separate a dehydration effect from a genuine loss of filtration.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.