Evaluation of the Sidekick point-of-care progesterone lateral-flow assay for use in equine reproductive management.

Research Overview

• This study evaluated the effectiveness of the Sidekick, a point-of-care progesterone test device for horses, comparing its accuracy and reliability with established laboratory methods.
• The goal was to determine if the Sidekick could provide rapid, accurate progesterone measurements to improve equine reproductive management directly at the stall-side.

Purpose and Importance of the Study

• Progesterone measurement is critical in managing equine reproduction, as it helps in monitoring the mare’s reproductive cycle and pregnancy status.
• Traditional progesterone assays like radioimmunoassay (RIA) and chemiluminescence immunoassay (CLIA) require laboratory processing, causing delays.
• A rapid, accurate point-of-care (POC) device could enable immediate clinical decisions, improving reproductive care efficiency.

The Sidekick Device and Progesterone Lateral-Flow Assay (LFA)

• The Sidekick device uses a progesterone lateral-flow assay, a rapid test format similar to a pregnancy test, combined with an electronic reader for quantifiable results.
• This setup offers quick progesterone level readouts at the stall-side without needing lab equipment.

Analytical Performance Evaluation

• Researchers tested serial dilutions of mare plasma with known progesterone concentrations (ranging from 0 to 8 ng/mL) to assess the Sidekick’s accuracy and precision.
• Key metrics included:
  • Percent recovery: How close the test’s result was to the true concentration (Sidekick showed 90-102% recovery between 4-8 ng/mL, indicating high accuracy).
  • Repeatability: Consistency of results when the same sample is tested multiple times (Coefficient of Variation [CV]: 4-15%, demonstrating strong repeatability).
  • Reproducibility: Consistency of results across two different labs (CV: 9.9%, indicating good reproducibility).

Clinical Accuracy and Agreement with Established Methods

• Nineteen paired serum samples were tested by the Sidekick device and compared to RIA and CLIA results.
• Agreement was measured through regression analyses and ordinal concordance (κ, kappa statistic) across progesterone ranges relevant to clinical decisions.
• Findings demonstrated:
  • Near-perfect agreement with spiked samples (κ = 0.94), indicating the Sidekick accurately detected known progesterone levels.
  • Substantial agreement with clinical samples compared to RIA (κ = 0.77) and CLIA (κ = 0.79), showing the device’s results closely matched established assays in real-world samples.

Cross-Reactivity Testing

• The study assessed whether the Sidekick test reacted with altrenogest, a synthetic progestin drug commonly administered to mares.
• No cross-reactivity was detected at pharmacologic concentrations, meaning the Sidekick specifically measured natural progesterone without interference from altrenogest.

Limitations Identified

• An observed bias was noted that could arise from differences in sample matrices: the Sidekick used plasma, while the reference methods used serum.
• The narrow validated range of the Sidekick (up to 8 ng/mL) might underestimate progesterone levels when concentrations are higher than this range.
• These factors should be considered when interpreting results, particularly at very high progesterone levels or comparing plasma versus serum.

Conclusions and Implications for Equine Reproductive Management

• The Sidekick lateral-flow device reliably provides rapid and accurate progesterone measurements within the clinically important concentration range (4-8 ng/mL).
• Its rapid results facilitate on-the-spot reproductive decisions by veterinarians or breeders.
• Using the Sidekick could reduce delays caused by sample processing and laboratory testing, potentially improving reproductive outcomes in horses.