FeLV testing - how old? use an ear prick?

One vet just told us that the kitten needs to be 1lb to be tested for FeLV. Any idea why? From what I'm finding online, a kitten can be tested at any age for FeLV. Could the 1lb limitation be because the kittens veins are too small? But there's always the neck. This particular kitten is about 4-5 weeks old (found crossing a busy street!). He needs to be fostered but we don't want to infect any other cats/kittens because we haven't tested.

Also has anyone see any data on using blood from an ear prick (vs vein) for ELISA tests. Cat Fanciers website says a blood sample. Why not an ear prick? I read that saliva/tears isn't recommended due to false readings + or -. As a rescue, we can buy the snap tests from IDEXX directly at a discounted rate and do the tests ourselves. Obviously, an ear prick would be much easier than drawing blood.

 

The shelter tests all kittens big enough to get blood from.. but I do not know if capillary blood is ok. What I was reading said serum, plasma or whole blood but didnt specify venous or capilary. You need more than a drop for the Snap test. you need at least 3 drops, so I dont think you would get enough blood with an ear prick.

 

The test requires a blood sample with a certain amount of blood. This needs to be venous blood, so you cannot draw from an ear.

It is very difficult to draw blood from a kitten below 1 lb, and the blood taken may be significant enough to cause undue danger to the kitten.

As for drawing from the neck, we had a VET draw from the neck of one kitten who was 2 1/2 lbs, and thank GOD we dallied - somehow the vein didn't clot right and the kitten began passing out in front of us! Vet saved his little life, but it COULD have ended trajically. They are just so fragile at that age, it is safer to wait.

I would recommend fostering him in isolation - keep him in a bathroom, a walk-in closet inside a bedroom. As long as you can have him separated from others, things will be fine until he can be tested.