Re: Requirements for ACTH Testing?


Hi Ferne,


Not sure if the following will apply.

If also doing glucose, and there will be a 1 hour delay in separating the cells, the vet needs to use a grey top tube, not a red top tube for the glucose sample.  Also keep it chilled with the lavender top tube to slow bacterial growth. The grey top tubes might need to be ordered so make this request to your vet well ahead of time. 


To avoid confusion, mark on the submission form that the grey top is for the glucose test.

The additives in the grey top tube can interfere with other tests, so use this one just for glucose. 

For labs that require serum for insulin, use a red top tube for that. 

(Cornell uses the lavender top plasma for both ACTH and insulin).


We have a plastic ice cream container with refrigerated water plus ice that goes out to the barn when the vet arrives for the blood draw.  After gentle inversion to mix, all the tubes go into the ice water bath immediately, then the whole container with lid is transported in a pre-cooled (refrigerated) cooler bag, even though the vet’s office is only a few minutes away.


The following posts are by Dr Kellon:

“…sample should be kept cool (not frozen) and if they won't be able to process the blood within an hour (serum) or even sooner (plasma), should use a grey topped tube (fluoride) for the glucose test. This tube stops the red cells from eating up the glucose giving you a falsely low result.”

“One big problem though is that glucose levels will tend to degrade for as long as the blood cells are in contact with the serum, and over time because blood is not collected sterilely and some bacteria inevitably get into the sample. If you get a low reading, first to do is probably repeat it. Either borrow a human glucometer if you can, or request a glucose be run using a grey top collection tube (oxalate - stops the red cells from "eating" the glucose).”

       [*my note for newcomers- need BOTH Glucose and Insulin from the SAME blood draw]

“Just a quick note here on glucose testing. Unless you are doing a complete chemistry panel (which needs serum), ask your vet to take the sample for glucose into a grey top tube (oxalate). This will give you more accurate glucose readings.”


For Info on tubes:


On rates of glycolysis:

“Both red cells and leukocytes contain glycolytic enzymes. Therefore glucose will be consumed and the concentration of glucose in a sample of whole blood will decline with time. The rate of loss is generally said to be approximately 5% per hour, but may be as rapid as 40% in 3 hours. Consumption of glucose in whole blood samples can be prevented by adding sodium fluoride to the specimen to inhibit the glycolytic enzymes.


Rapid separation of the sample or cooling will also prevent glycolysis and will allow the sample to be used for other determinations. Unhemolyzed samples that have been separated within 30 minutes of drawing are generally considered adequate. Rapid cooling of the sample followed by centrifugation is even more effective in preventing glycolysis. “


SW Ontario,  Mar 2005

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