Macroprolactin

Macroprolactin is a large, inactive form of prolactin (a hormone that regulates milk production and reproductive function). It is measured to distinguish it from regular prolactin, since high macroprolactin can cause false elevations in total prolactin tests without causing actual symptoms.

When elevated: Elevated macroprolactin suggests that a high total prolactin result may be a laboratory artifact rather than a true hormonal abnormality. This can prevent unnecessary investigation or treatment for conditions like pituitary tumors or hypogonadism. When low: Low macroprolactin is not clinically significant; the focus is on whether macroprolactin accounts for an elevated total prolactin level.

Macroprolactin is not directly performance-relevant for most athletes. However, elevated prolactin (from any source) can impair testosterone production and recovery in male athletes, or disrupt menstrual cycles and bone health in female athletes—so distinguishing true prolactin elevation from macroprolactin helps clarify whether hormonal support is actually needed.