Maximizing Serum Zinc Testing

As an avian clinician you’re probably well aware of the harmful effects of zinc ingestion by birds, and the sometimes tedious task of tracking down the source, be it cage wire, bird toys, keys, or, paints, skin preparations, or even suppositories formulated with zinc. Needless to say, sample handling techniques that disqualify or greatly mask the accuracy of serum zinc diagnostic testing is just not acceptable. There is some belief that certain media used for serum transport can cause artifactual effects on zinc testing. Even some clay brands used in filling hematocrit tubes was thought to adversely affect zinc levels. Many laboratories may, in the face of questionable zinc results, introduce these possible contributors, and then partially dismiss the results. We’ve been tracking the zinc testing going on in our facility and with the help of Dr. Jowett at Louisiana State University, we’ve decided in our desire to maximize the accuracy of our zinc diagnostics, some investigation into what would be the best choices of media to use is in order. Here’s what we came up with: We’ve looked into several cases, but these three best demonstrated the trends we’ve been seeing. Below are comparisons of sample suspension using plain (no anticoagulant) serum tubes, Sarsted brand tubes, and hematocrit tubes using Critoseal clay.

Zinc Results (ppm)
Pet Name Species serum tube Sarsted tube Critoseal clay*
Appalacion blue throat Macaw 1.7 3.1 1.8
Sabrina sulfur crested Cockatoo 1.7 4.0 1.9
Pig** moluccan Cockatoo 2.5 3.8 2.7
*Critoseal brand clay (white in appearance).
**Adams clay (yellow modeling type clay) was also tested in this case. The result was reported at ~23.4 ppm, as compared to 2.5 ppm using the plain serum tube, shown above. The bottom line.
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