PCR and Pooled Testing

You’ve probably heard of PCR testing for Covid, but what is pooled testing?

American Society for Microbiology
How does a PCR test work?

Basically, it looks for genetic material from the virus. This is the most common and most sensitive type of test for Covid-19.

What is pooled testing?

Pooled testing means taking samples from multiple people, combining the samples into pools, and then testing each pool.

Pooling Systems That Have EUAs

For a very brief overview of each of them, click on the header. To see the FDA’s list, click on the FDA logo above and search for “pooling.”

On 04.20.2021, the FDA made it easier for labs that do screening at least once a week (for example, labs that screen folks in schools) to get EUA for their pooling systems.

Ginkgo leaf. Image by Ulrike Leone from Pixabay.
Labs Don’t Need EUAs
To Pool Samples
(Boston Globe, 01.22.21)

Legally, labs don’t NEED EUAs to pool samples. But having an EUA means someone besides the lab itself has taken a look at the pooling system and is relatively confident that it works.

This article features two labs with internally validated pooling systems: Ginkgo Bioworks and Mirimus.

Photo by NeONBRAND on Unsplash
Pooling can save money, at least in theory.

This preprint paper indicates that pooling can save money – for the testing company, at least. YMMV.

Does it matter how you organize your pools?

Yes, because if you have a strong positive in a pool, you’re more likely to pick up a weak positive in the same pool. This paper from the Hebrew University of Jerusalem explains why that happens, and why it means that your pools should be made of people who are in the same classrooms.

When is pooling NOT a good choice?

The general consensus is that pooling only makes sense if there’s a low prevalence of disease in your community – most folks use 10% prevalence as the cutoff. This paper shows data about when that’s true – and when it might not be.

CIC Health logo
You may not have to contract directly with a lab.

Testing-services companies like CIC Health can provide all the client-facing services that schools need; they may even be able to shop around at different labs and find the best price for you.

(Disclosure: The Harvard Public School system is contracting with CIC Health to provide pooled PCR testing.)

A 10×10 matrix. Image by Alan McNally and Jonathan Ball.
What is matrixed pooling?
(The BMJ Opinion, 09.30.20)

“In two-way pooling, a grid or matrix of samples are formed, and column and row pools are generated and tested. In the example shown . . . 100 samples are pooled using a 10×10 matrix to produce 20 pools for testing. Only the samples that lie at the intersections of positive columns and rows then need to be tested to identify the positive ones.”

Unless you’re used to reading opinion articles in scientific journals, just scroll down until you reach the graphic above. The caption explains the basics.

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