Sample instructions to improve vitamin and trace mineral test results
Cat Barr, PhD, DABT
The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) has recently updated the sample requirements for Vitamins A and E in serum and for Trace Mineral Panels in whole blood and serum samples.
For the serum vitamins, a hemolysis limit will be imposed.
“Hemolysis releases enzymes into the serum that can speed up degradation1,2 of vitamins A and E,” explained Analytical Chemistry Section Head Travis Mays, PhD. “Particularly in hot weather we have trouble with serum samples shipped on the clot ending up really hemolyzed. We are now rejecting serum samples for vitamin A or E testing if they are visibly hemolyzed at over 100 mg hemoglobin/dL.”
A handy tool for evaluating hemolysis in serum samples can be found on the Centers for Disease Control and Prevention’s website. This chart is the same one used by TVMDL.
In addition, it’s important to protect samples for vitamin A or E testing from light and heat – especially vitamin A. Shipping overnight on cold packs and wrapping samples to block out light helps prevent vitamin degradation. Foil can be used as long as it doesn’t come in direct contact with the sample. For example, liver should be placed in a plastic bag first.
Hemolysis also affects trace mineral results.
“It’s logical that opening up red blood cells and dumping the contents into the serum would raise the iron concentration – all that hemoglobin3,” Mays said. “Opening those cells also releases extra zinc4 and manganese, so those are increased from what they would be in clear serum, as well.”
For best results on Trace Mineral Panels and Metal & Mineral Panels, two separate tubes should be submitted: one tube with EDTA whole blood (not centrifuged) and one tube with clear serum, pulled off the clot and shipped in a clean tube.
Trace Mineral Panels can be performed just on serum, but using whole blood as well gives the advantage of being able to measure selenium in a longer term sample because it includes the red cells.
“Selenium in the serum more closely indicates what the animal consumed that day,” Mays said. “And of course if you’re worried about zinc – whether deficiency or poisoning – it’s important to avoid using any rubber stoppered tube other than the royal blue tops.”
Royal blue stoppered tubes are manufactured without the zinc that variably contaminates all other colored rubber stoppers.
“Another way to avoid zinc contamination is to use an entirely plastic tube,” he continued. “And since hemolysis falsely increases serum zinc concentrations4, transfer the serum to a second clean all plastic or royal blue topped tube for shipping.”
Taking these extra steps to submit the optimal samples will increase the value of the results TVMDL can generate for your patients.
For more information on TVMDL’s test offerings, visit tvmdl.tamu.edu or call one of the agency’s four laboratories.
1 Marinovic et al, 1997: Effects of hemolysis on serum retinol as assessed by direct fluorometry. Am J Clin Nutr66:1160-1164.
2 Hooser et al, 2000: Effects of storage conditions and hemolysis on vitamin E concentrations in porcine serum and liver. J Vet Diagn Invest 12:365-368.
3 Nishiie-Yano et al, 2020: Hemolysis is responsible for elevation of serum iron concentration after regular exercises of Judo athletes. Biological Trace Element Research 197:63-69.
4 Killilea et al, 2017: Identification of a hemolysis threshold that increases plasma and serum zinc concentration. J Nutrition, doi:10:3945/jn.116.247171