How much does creatinine blood level fluctuate in time in one person, within a year? What everything can influence it?

Creatinine level . Should remain stable in a year or long period of time. It gets worse or increases in value when there's kidney problem, dehydration, adverse effects of hypertension, diabetes, medications, IV contrast dyes, creatinine products, autoimmune conditions, muscle breakdown/rhabdomyolysis, heart/liver or kidney failure etc.
Less than 10% Under normal circumstances, creatinine levels do not vary by more than 10% over a year. Dehydration and change in renal function and cardiac output are common factors affecting creatinine. See this site for more info.