Your Doctor will use a purple top (EDTA) tube to test the Insulin and ACTH at the same time or a plain red top tube (SST/Tiger tops/Red Tops with gel at the bottom are not to be used due to creating a false low hormone numbers by pulling hormone into gel.) to test Insulin and Glucose (and Thyroid if needed).
Blood tubes have expiration dates on them. Old tubes do NOT draw in the right amount of blood due to the seal of rubber at the top dies out, so air gets into the tube and the vacuum is less.
Purple top blood tubes are common and easy to get. Plain red top tubes require special ordering: Fisherhealthcare.com at 1-800-640-0670. 10 ml plain red top serum tube made of plastic. Catalog #: 02-683-60, MFG #366441.
If pulling for ACTH, Insulin, Glucose, and Thyroid need a purple and a red top. Pull red top first to avoid EDTA getting into red top. All tubes according to maker, require you to roll the tube gently 8 times for complete mixing and uniformity.
Next, put tubes in refrigerator to cool down. This slows the cells from metabolizing Glucose and from Insulin, Thyroid and ACTH levels from dropping (creating a false low number). Keep tubes upright in refrigerator to avoid contact with rubber tops. Do not lay on side.
Next, after 30 minutes, spin blood in a centrifuge. You can use your car’s cell phone charger to power it. A Black and Decker converter plugs into the cord of the centrifuge and you will spin at 3000 rpm (standard high on most centrifuges) for 5 minutes. This allows the Vet to go on calls after blood drawn and not have to race back to the clinic, or have samples be unspun too long creating false low numbers. Glucose levels that are very low (65, 52, 28 mg/dl….) indicate the sample was mishandled, and results need to be tossed out and the horse retested. Very low Insulin numbers after a Karo Syrup Challenge (under 20 uml – Cornell) also would be suspect of the sample not being spun quickly or of a sample getting heated up in transit to the lab (not in a cooler as required).
Once spun, serum or plasma is transferred to a plastic tube using a sterile syringe and needle or sterile pipette. You only need 2cc of serum or plasma to do tests. Do NOT use the blood tube to transport sample to lab. The rubber top on it will alter results. A hard plastic tube like in the picture also can be bought at Fisherhealthcare.com at 1-800-640-0670. Put the pulled off serum or plasma in the plastic tube and put back in the refrigerator.
The samples can be frozen prior to shipping (required if ACTH being tested also) or refrigerated prior. They must be sent FedEx-Urgent – Next Morning – in a refrigerated pack.
only to labs that test Insulin dozens of times a week and with Board-Certified Clinical Pathologists on staff. There have been many problems with private labs. Take it out of the equation.
Only send in USA to:
Cornell Veterinary School Diagnostic Lab – 607-253-3673
Michigan State Veterinary School Diagnostic Lab – 517-353-1683
Colorado State Veterinary School Diagnostic Lab – 970-297-1281
In Canada send to:
Guelph Ontario Veterinary School – 519-824-4120 ext. 54530
In Europe send to:
Royal Veterinary College (England) – 01707 666208
Why did we wait 60-75 minutes after Karo Syrup to pull blood? This is when Insulin peaks in horses – approximately triples from resting and peaks at this time. The peak of Insulin in normal horses is 60 unu (430.5 pmol)
Horses and humans both peak in Insulin at the same time,
Dr. M. Roberts, Eq. Vet Journal – University of Bristol
Dr. L. Lawrence, University of Kentucky
Dr. S. Ralston, Rutgers University
Dr. J. Bland, LSU Animal Science Dept.
after meals and after a Glucose Challenge.