Serum creatinine 0.49mg/dl, 24h urine cr 22.1mg/dl & cr excretion 884mg, cr clearance 125.4ml/min, random urine cr 109,7mg/dl. normal? if low, why?

Normal: All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Having said that, your results are normal. Serum creatinine levels depends, in part, on muscle mass and women have lower levels than men.

Just ignore this: Labs are set so that a few percent of healthies fall outside on either end. This could not be due to illness. Be thankful for a normal creatinine clearance and that your physician took time to check it.