Technical Manager Boehringer Ingelheim Animal Health USA Inc. Stewartsville, Missouri, United States
Abstract: Hypothesis: Compared to resting (T0-ACTH), dynamic ACTH evaluation 30 min after TRH-stimulation (T30-ACTH) will provide more reliable diagnostic for PPID. T30-ACTH diagnostic cut-off values will be established.
Animals: The protocol was approved by the Institutional Animal Care and Use Committee, with 15 PPID-positive, 15 PPID-negative horses used.
Methods: In Fall and Spring, blood samples collected before and 30 min after 1 mg TRH i.v. were analyzed using the Immulite assay. Using T30-ACTH, the upper 95% level of PPID-Negative horses and the lower 95% level of PPID-Positive horses quantified highest Negative and lowest Positive diagnostic limits.
Results: During Fall: Mean±SE of T0-ACTH and T30-ACTH, respectively, was 56.8±13.4 and 98.4±19.9 pg/mL in PPID-Negative; 229±63 and 547±106 pg/mL in PPID-Positive. The T30-ACTH 95% Confidence Interval was 55.8–141 pg/mL in PPID-Negative, 320–774 pg/mL in PPID-Positive horses. Recommended Fall cutoffs are PPID-Negative < 141 pg/mL and PPID-Positive >320 pg/mL.
During Spring: Mean±SE of T0-ACTH and T30-ACTH, respectively, was 13.8±2.5 and 21.5±3.9 pg/mL in PPID-Negative; 129±81 and 300±107 in PPID-Positive. The T30-ACTH 95% Confidence Interval was 13.1–30.0 pg/mL in PPID-Negative and 70–530 pg/mL in PPID-Positive horses. Recommended Spring cutoffs are PPID-Negative < 30 pg/mL and PPID-Positive>70 pg/mL.
Conclusions: PPID-Negative horses showed similar variation for T0-ACTH and T30-ACTH during Fall and Spring, but PPID-Positive horses had greater variation at T0-ACTH vs T30-ACTH during Fall and Spring, suggesting T30-ACTH is a more reliable test.
