Vaginal bleeding occurs in females of reproductive age, meaning between the age of menarche, which happens around 11, and menopause, which happens around 50.
Normal vaginal bleeding is called menstruation, and it usually lasts less than 8 days, and no more than 80 milliliters—or slightly less than 6 tablespoons—of blood are lost.
The first day of menstrual bleeding marks the beginning of the menstrual cycle, which normally repeats itself every 24 to 38 days.
Additionally, normal menstrual cycles are regular, meaning that the shortest and longest cycles in a 12 month period don’t usually vary by more than 9 days.
Pathological vaginal bleeding, or “abnormal uterine bleeding”, on the other hand, describes any variation in normal bleeding patterns - in terms of age, frequency, regularity, duration, or volume.
Age-wise, any kind of bleeding is considered abnormal before menarche and after menopause.
Abnormalities in frequency and regularity can mean that cycles either occur irregularly, or that they are very short or very long. This also includes unscheduled intermenstrual bleeding - bleeding between cycles.
Finally, volume-wise, vaginal bleeding that is profuse enough to cause changes in hemodynamic status, even in the context of an otherwise normal menstrual cycle is considered pathological.
So, the first step in assessing vaginal bleeding is checking the hemodynamic status, by looking for signs of hypovolemia.
Mild hypovolemia can cause mild tachycardia and orthostatic hypotension, whereas severe hypovolemia can cause severe tachycardia, hypotension, oliguria and delayed capillary refill.
If there’s hypovolemia, lab work includes a CBC, which usually shows a normal hemoglobin level, because the individual is losing whole blood.
Over the next 24 hours, there’s a physiologic compensation of holding onto more water, and IV fluids are usually given - and that decreases the hemoglobin level.