Accurate measurement of parathormone (PTH) and ionized calcium (Ca 2+) requires that serum be anaerobically transferred from the spun SST or RTT [using a syringe and needle to avoid air exposure] into a plain RTT. Clearly label the sample tube as SERUM and freeze or send immediately on cold packs. Samples that have been exposed to a LTT ir may have artificially decreased Ca2+ , whereas those sent in SST may have artificially increased Ca2+.

Like the dog, serum relaxin measurement (Witness® Relaxin Assay, Synbiotics Corp., San Diego, CA) has been validated as an accurate, noninvasive and useful assay to confirm pregnancy in the cat. A recent study found 100% sensitivity and 91% specificity after ~25 days of gestation, with a positive predictive value of 93% during and after the second trimester. Sample required is 0.5 ml of separated heparinized or citrated plasma. Serum and EDTA-anticoagulated samples are not acceptable. TAT is 2-5 days.

Platelets stored in EDTA (LTT) for up to 72 hours remain in resting state but form platelet-surface associated immunoglobulin G (PSA IgG).

These results have important clinical implications for the diagnosis of immune-mediated thromboctopenia , as samples more than 24 hours old can give false-positive test PSA IgG test results.