Do PCR (polymerase chain reaction) tests for coronavirus pierce the blood-brain barrier? No, that's not true: There's no way for a nasal swab to reach the barrier without going through bone, according to a leading public health expert who has studied the Covid-19 virus.
The claim appeared as a Facebook post (archived here) on July, 6, 2020. It opened:
This is HUGE!!!! The spot where they are "getting a sample" for the Covid-19 test is called your Blood-Brain Barrier. It is a single layer of cells that protect your brain from heavy metals, pesticides & other toxic substances that are usually kept out. It is the way vital nutrients, like oxygen, reach the brain.
This is what the post looked like at the time of writing:
(Source: Facebook screenshot taken on Tue Jul 7 14:54:10 2020 UTC)
It continued:
If, in some way, your Blood-Brain Barrier is compromised, it becomes a "Leaky Blood-Brain Barrier" which is an inflamed brain! It then allows bacteria & other toxins to enter your brain & infect the brain tissue which can lead to inflammation and sometimes death.
Lead Stories reached out Thomas Hartung, MD, a professor at the Johns Hopkins Bloomberg School of Public Health, to verify the post's claims. Here's what he wrote:
This information is wrong. The blood-brain-barrier is the barrier between the blood vessels in the brain (endothelial cells) and the brain (formed by a helper cell, i.e. astrocytes). It is a microscopic structure. No way to reach any of this from the nose - there is a mucus membrane, bones of the scull, meninges, cerebrospinal fluid etc. between.
In other words, the post is correct in stressing the significance of the blood-brain barrier, but it's wrong about almost everything else.
The job of the blood-brain barrier is built into its name; its meant to act as a barrier between our blood and brain, preventing circulating pathogens from getting to the brain. The barrier is not a solid wall, though. It allows nutrients to pass through.
It's true that the barrier can be compromised in a number of ways. Some bacterial infections, certain neurological diseases and inflammation are all ways in which the barrier could be damaged.
But swabbing to test for coronavirus? That's not going to compromise the blood-brain barrier. As Hartung wrote:
You cannot reach the brain from the nose without going through bone.
