Grey Top Tubes (Sodium Fluoride)
This tube stabilizes the specimen’s glucose component during transport. It must be at least 50%
filled or the high concentration of sodium fluoride will interfere with glucose testing methods.
The preferred method to stabilize a specimen for glucose and other chemistry assays is to collect
a serum separator tube (SST), and centrifuge it after it clots to separate the serum from the blood
cells. Alternately, draw a plain red top tube (RTT), centrifuge it, and transfer the serum to another
RTT.
Therapeutics
Drugs such as digoxin and phenobarbitol are most stable in blood samples drawn into a RTT, as the
silicone gel of SST will absorb many drugs. Vitamin B12 and folate levels also may be affected by
the SST gel, although elemental therapies such as bromides do not appear to be altered.
Blood Culture
Specimens for blood culture require collection into a specialized vacuum culture bottle containing
growth medium. The venipuncture site should be shaved, scrubbed clean with soap and water, and
disinfected twice with an iodine preparation. Allow the site to dry. The rubber stopper of the
culture bottle should be disinfected with alcohol. Obtain 1-3 mL blood using a needle and syringe,
and transfer immediately into the culture bottle. Multiple blood cultures increase the chance of
detecting bacteremia. Draw 2–4 bottles taken 1–2 hrs. apart with the animal off all antibiotics
for at least 2 days. Leave culture bottles at room temp during transport.
Coagulation Testing
Blood samples for coagulation testing must be drawn into a blue top tube (BTT). The BTT should be
filled to at least 75%, but preferably 90% or more capacity, as results will be affected by excess
citrate anticoagulant. Centrifugation and separation of plasma from cells is preferred if transportation
to the laboratory takes more than 12 hours. Use a plastic pipette or small syringe to transfer the plasma
to a clean plastic tube. Cap the plasma tube and keep cold or freeze at -20°C or lower. Freezing the
plasma is not necessary unless testing will be delayed for more than 24 hours, but it should always
stay cold. Repeated freezing and thawing of plasma denatures coagulation proteins. The Antech drivers
have coolers to transport local samples. Samples being mailed should be shipped overnight with frozen
cold packs.
Plasma von Willebrand factor can be measured in samples collected in either BTT (preferred) or lavender
top tube (LTT), following the guidelines above.
Endogenous ACTH
Aprotonin (protease inhibitor) is added to a LTT to stabilize ACTH so freezing the sample is not needed.
[Tubes are available from ANTECH.] The treated plasma should be separated immediately by centrifugation,
transferred to a plastic tube, capped and refrigerated. Transport sample to the lab with cold packs.
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