A toxic substance in many COVID-19 rapid at-home antigen test kits could be harmful if the extraction tube containing the chemical is used improperly, according to the National Capital Poison Center.

The substance, sodium azide, is a liquid reagent used as a preservative that triggers a chemical reaction after contact with a nasal swab, which determines if the test is positive or negative. It’s found in several rapid antigen kids, including BinaxNOW, Flowflex, BD Veritor and Celltrion DiaTrust.

“Sodium azide is a very potent poison,” says the National Capital Poison Center, which is not a government agency, “and ingestion of relatively low doses can cause significant toxicity. Fortunately, the amount of sodium azide in most rapid antigen kits is much lower than the amount expected to cause poisoning if swallowed by an adult.”

A concentration of 0.0125 percent is used in the BinaxNOW test kit, according to the Food and Drug Administration.

The health threat only appears when the kits are misused. In one case, a couple dipped the nasal swabs into the reagent solution first before swabbing their nostrils, causing irritation in the area, according to Poison Control. Some users have mistaken the reagent containers for eye droppers. The plastic packaging, indeed, can look like single-dose eye drops or other common products.

“I would follow the directions of the kit,” says Dr. Ulysses Wu, Hartford HealthCare’s System Director of Infection Disease and Chief Epidemiologist. “That’s how it was studied and that’s how they produced it. I would not deviate from any of those instructions.”

If swallowed, sodium azide can cause dizziness, low blood pressure, headache and heart palpitations. Seizures, loss of consciousness and death are possible in more severe cases.

Most cases reported nationwide have been minor.

Here are some safety recommendations.

  • Before testing: Read the directions carefully.
  • After testing: Dispose of all kit contents in outdoor trash container. Wash hands thoroughly.
  • Eye exposure: Rinse for 15-20 minutes with warm tap water.
  • Skin exposure: Rinse well with tap water.
  • If ingested: Poison Control does not recommend intentional vomiting. Call 1.800.222.1222 for guidance.
  • Precautions: Keep all test kits away from children. Treat the kits like a prescription medication: Store in a cabinet, out of reach of small children, and lock if possible.

If you believe someone in your household has been exposed to sodium azide: Call Poison Control at 1.800.222.1222. Also available: Poison Control online tool.