In general (90 plus percent of the time) elevated creatinine means "renal insufficiency" or the lack of adequate cleaning of the blood. Creatinine is a marker for kidney function and is usually right but in few instances its not. I can think of a few tricky or exotic situations when the creatinine can be elevated but renal function is normal. As a final comment I would like to add that few people look at the creatinine alone, most will look at both the BUN and the creatinine.
The tricky situations I can think of are as follows:
If you become "dehydrated" or don't drink enough water your kidneys may not be able to clear creatinine, function might still be normal.
If you eat a large steak your level of creatinine might go up because you are eating the animal's creatinine stored in the muscle. Your kidneys still work fine.
If you are a body builder and you have too much muscle, your creatinine might be high but your kidney function normal.
A drug might interfere with the measurement of creatinine and cause it to be falsely high (known as Jaffee Reaction)
In a crush injury muscle may be crushed and release creatinine, its difficult to tell what the kidney function is.
Some other exotic conditions.
The real answer is 99% of the time yes, if your creatinine is high your kidneys are not working well.