Age and sex as predictors of biochemical activity in acromegaly: analysis of 1,485 patients from the German Acromegaly Register - Petersenn, S; Buchfelder, M; Gerbert, B; Franz, H; Quabbe, H J; Schulte, H M; Grussendorf, M; Reincke, M; Participants of the German Acromegaly Register (Clin Endocrinol (Oxf), 2009)