Venepuncture causes rapid rise in plasma ACTH.

Serum cortisol and adrenocorticotropin (ACTH) levels were measured on nine sleeping volunteers at midnight, before and after the stress of being woken and exposed to a single standard venepuncture. In six volunteers, plasma ACTH levels were raised within 90 seconds of venepuncture, while it remained undetectable in the other three. Cortisol levels began to rise within 4 minutes. ACTH and cortisol levels may be greatly altered by the stress of venesection. Plasma ACTH measured after a difficult venesection in a subject with poor venous access may be misleading.