Module 4: Polymerase Chain Reaction (PCR)

Module 4.4: Real-Life Example

Clinical Scenario

You are working in a large shelter and there has been a recent outbreak of kennel cough. You decide to run an RT-PCR Respiratory panel to get a better understanding of the potential respiratory pathogens in the shelter and aid in the development of isolation, control, and vaccination protocols. You chose 4 sick dogs to run the RT-PCR respiratory panel on. The following are results from the Pneumovirus RT-PCR data on those 4 sick dogs.

Dog 1 has a negative result and an undetermined Ct value. Dog 2 has a positive result and a Ct value of 36.0251. Dog 3 has a positive result and a Ct value of 20.1314. Dog 4 has a positive result and a Ct value of 37.0096.
RT-PCR respiratory panel results for 4 sick dogs

Reference interval interpretation

Table 4.1: Reference interval interpretation for RT-PCR respiratory panel

Cycle Threshold (Ct)


Ct < 29 Strong positive
Ct 30-37 Moderate positivity
Ct >38 Weak positive

Knowledge check

Key Takeaways

  • PCR is an amplification technique that allows for the detection of genetic material in very small amounts
  • PCR testing is not always the best choice as an infectious disease screening tool
  • This test is very sensitive and very specific
  • High CT values may be an indicator of a false positive
You have now reached the end of Module 4. If you are enrolled in CVM 6925, please go to the Canvas page and take the quiz: “Module 4: Intro to PCR quiz.” There is not an assignment or in-person laboratory associated with this module.


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Clinical Veterinary Diagnostic Laboratory Copyright © 2021 by Erin Burton is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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