Veterinary Blood Tubes: A Quick Guide to Which Tube to Use
Blood tubes are one of those things you use all the time in veterinary practice — and still occasionally stop and think, “Which one do I need again?”
Whether you’re in clinic, on placement or still getting used to pathology sampling, knowing which tube goes with which test can save time and help avoid rejected or unusable samples.
The exact requirements can vary between laboratories, so always check your lab’s current submission guidelines when you’re unsure. But as a general guide, here are some of the most commonly used veterinary blood tubes and what they’re used for.
EDTA tubes
EDTA tubes are commonly used for haematology, including routine full blood counts.
EDTA prevents the sample from clotting while preserving the blood cells well enough for haematological assessment. Cornell’s veterinary diagnostic laboratory notes that EDTA-anticoagulated blood is its standard sample for routine haematology testing.
One practical point worth remembering: avoid severely underfilling an EDTA tube where possible, as having too much EDTA relative to the amount of blood can affect cell morphology and some measured values.
Serum tubes
Serum is commonly used for biochemistry, endocrinology and many serological tests.
The blood is allowed to clot before the serum is separated from the cells. Cornell notes that serum is generally preferred for chemistry testing in its laboratory, although individual laboratory requirements vary.
If there is going to be a delay before testing, appropriate sample separation and storage become particularly important.
Lithium heparin tubes
Lithium heparin produces plasma rather than serum and can be used for a range of chemistry testing depending on the laboratory and test.
However, it isn’t interchangeable with serum for every test. Australian veterinary laboratory Vetnostics, for example, generally requests serum rather than lithium heparin for routine biochemistry and endocrinology because submitting lithium heparin may limit the available testing.
This is a good example of why checking the requirements of the laboratory you use is important.
Sodium citrate tubes
Sodium citrate tubes are most commonly associated with coagulation testing.
These tubes rely on a specific ratio between blood and anticoagulant, so filling them correctly matters. Underfilled citrate tubes can produce unreliable coagulation results.
Cornell specifically notes that the citrate-to-blood ratio is critical and recommends recollecting samples that are not filled to the required volume.
Vetnostics similarly advises that citrate tubes should be in date and filled appropriately.
Does the order of draw matter?
It can.
When several tubes are being collected from the same patient, the order in which they’re filled can help reduce contamination between tube additives.
Vetnostics notes that using the correct order of draw helps prevent contamination of serum with additives such as EDTA or fluoride oxalate and can also help minimise activation of coagulation factors in citrate samples.
Your laboratory’s current collection guide is the best place to check the recommended order.
A few practical sampling reminders
Good sample collection matters just as much as choosing the right tube.
Try to minimise traumatic venepuncture and haemolysis, gently mix anticoagulant tubes as recommended rather than shaking them, and make sure samples are labelled correctly before they leave the patient.
Storage and transport requirements also vary depending on the sample and test, so check your laboratory guidelines if there will be a delay before analysis.
Keep the information somewhere easy to find
There’s nothing wrong with double-checking which tube you need — particularly when you’re busy, learning or dealing with a test you don’t collect very often.
That’s exactly why we made the VetVital Veterinary Blood Tube Reference Card.
It keeps commonly used blood tube information in a compact, waterproof format that can stay on your lanyard and be checked quickly when you need it.
[SHOP THE VETERINARY BLOOD TUBE REFERENCE CARD]
VetVital reference cards are designed as quick clinical reference tools. Laboratory requirements and testing protocols can vary and may change over time, so always refer to your diagnostic laboratory’s current submission guidelines where appropriate.