En. Behrend et al., EFFECT OF STORAGE-CONDITIONS ON CORTISOL, TOTAL THYROXINE, AND FREE-THYROXINE CONCENTRATIONS IN SERUM AND PLASMA OF DOGS, Journal of the American Veterinary Medical Association, 212(10), 1998, pp. 1564
Objective-To determine for dogs stability of cortisol, thyroxine (T-4)
, and free thyroxine (fT(4)) in plasma and serum stored in glass or pl
astic tubes at -20, 4, 25, and 37 C, Design-Prospective study. Animals
-Phase 1, 7 Greyhounds; Phase ii, 6 mixed-breed dogs. Procedure-Phase
I: blood was obtained after administration of thyroid-stimulating horm
one and adrenocorticotropin. Serum and plasma samples from each dog we
re divided into 8 aliquots, 4 in glass and 4 in plastic tubes. A pair
of aliquots, 1 in plastic and 1 in glass, were stored at -20, 4, 25, o
r 37 C for 5 days and then assayed for hormones. Phase II: blood was o
btained without prior stimulation. For fT, determination, serum from e
ach dog was placed in plastic or glass tubes, assayed immediately, sto
red at -20 C for 5 days, and reassayed, Aliquots from each dog were al
so stored for 1 day at 4 or 25 C and then assayed. Samples for cortiso
l determination were handled as in phase I. Results-Phase I: there was
no effect of tube type (glass vs plastic) on cortisol. Cortisol conce
ntrations decreased after storage in serum at 4, 25, and 37 C, and in
plasma at 37 C, compared with storage at -20 C. There was no effect of
sample type (serum or plasma) on T-4. Thyroxine concentrations increa
sed after storage at 37 C in glass, compared with storage at -20 C. Th
e fT(4) concentrations were lower in serum than plasma after storage a
t -20 C. Concentrations oi fT(4) increased after storage at 37 C in gl
ass, compared with storage at -20 C, Phase II: the fT(4) concentration
s did not change after storage in any condition. There was no effect o
f tube type on cortisol concentrations. Serum cortisol concentrations
decreased after storage at 37 C, compared with storage at -20 C. Clini
cal Implications-for cortisol, cooling of plasma is not necessary, but
serum should be shipped cold. For T-4 and fT(4), serum is sufficient;
contained within plastic tubes, samples can be shipped without coolin
g if assayed within 5 days.