Comparison of steroid and thyroid hormone concentrations in blood serum and plasma of captive tigers.

Analysis of steroid and thyroid hormones is often performed in blood serum. Occasionally though, plasma samples are submitted in lieu of serum for exotic species such as tigers. However, blood tube anticoagulants may affect hormone values. We compared serum and heparin plasma results for 7 hormones in tigers. Serum and plasma samples were collected from 25 tigers and analyzed for progesterone, 17-hydroxyprogesterone, cortisol, androstenedione, testosterone, estradiol, and thyroxine. Using Lin concordance correlation, serum and heparin plasma measures agreed for all hormones except cortisol. However, Passing-Bablok regression only found agreement between serum and heparin plasma measures for androstenedione, testosterone, and estradiol. Median values between the 2 sample types were significantly (p < 0.05) different for progesterone, 17-hydroxyprogesterone, cortisol, and thyroxine. Our results suggest that, for the aforementioned hormones, serum and heparin plasma values may not always be comparable.