>>I am beginning to get a suspicion about the lower level readings. The
problem with the levels is they need to be done a good while after feeding
or expressing, otherwise you get the surge with the feed and this muddies
the water so to speak.<<

"The concentration of prolactin in blod is highest immediately postpartum
and declines progressively by 6 mos postpartum. The suckling stimlus has
been demonstarted to stimulate the release of prolactin, which peaks 45min
after the commencement of a breastfeed. The concentration of prolactin in
blood returns to pre-feed levles within 3h of the beginning of a
breastfeed."  (citations within quote not included)  ---Cregan M, Mitoulas
L, Hartmann P. Milk prolactin, feed volume and duration between feeds in
women breastfeeding their full term infants over a 24 hr period.
Experimental Physiology 2002;87(2):207-14.

In accordance with the quote above, the best time to get a baseline reading
would be before the next feeding or at 3hours, whichever comes first. Best
time to draw for a surge would be 45min after start of feed.  Ruth Lawrence
suggests differently, to draw for the surge about 15 min into feeding
session. Take your pick. 

A while back I posted to lactnet about an article on the endocrinology of
lactation which had some interesting and sometimes questionable things in
it. That article quoted a pretty low "average" for baseline prolactin at a
pretty early stage of lactation. The population it was drawn from averaged
6-7 feedings, if I recall. If you think about it, the elevated level of
prolactin during lactation is in part due to the averaging of all those
surges. The more frequently they occur, the more prolactin is in the blood
stream. The longer the feeding interval, the longer the opportunity for
clearance. So baseline prolactin is both a function of a
normally-functioning endocrine system and the frequency of feedings. We need
to keep in mind these dual factors when assessing mothers.

Lisa Marasco

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