When, how and which COVID test

With a high demand for COVID-19 testing locally and throughout the nation, the County of Santa Clara Public Health Department is offering guidance to those unsure of what kind of test to use and whether or not they need one.

The testing options are a PCR test, typically administered in a clinic or drive-through operation; and an antigen test, which are also available for home use.

The County recommends that the antigen tests be used for purposes of shortening isolation or quarantine periods for those who have tested positive or been exposed to a person with COVID.

Positive antigen results should be recognized as valid – there is no need for a follow up PCR test at a healthcare or County facility.

In addition, people who have previously tested positive within the past 90 days should not get tested again during that time frame unless they have new symptoms – in which case they should use an antigen test.

PCR tests are generally more sensitive than antigen tests, but antigen tests are good at detecting when people are most infectious.  

The County also reminds patients of all healthcare systems that they have a right to a test from their provider if they have symptoms or have been exposed to an individual who has COVID-19.  Large healthcare systems remain subject to the Health Officer’s Testing Order.

The County of Santa Clara offers the following guidance to cover the fundamentals of COVID-19 testing.

You SHOULD get tested if:

  • You have new symptoms that might mean you have COVID: Fatigue, headache, body/muscle aches, cough, fever, sore throat, and/or congestion.
    • Please note that if you have new symptoms and you are at high risk for severe illness from COVID because of other medical conditions, older age, or having a compromised immune system, it is especially important to get tested because if you test positive, you may qualify for early treatment to reduce your risk of severe illness.

You MAY CONSIDER getting tested if:

  • It’s been 2-5 days after you have a known exposure to someone with COVID, especially if you are unvaccinated or have symptoms.

You SHOULD NOT get tested with PCR testing if:

  • You have already tested positive by a home/antigen test. Assume you have COVID and isolate accordingly. Do not get tested again at a testing lab – it is unnecessary and uses resources that could be used to test another individual.
  • You have tested positive in the last 90 days. You do not need get tested again unless you are newly symptomatic or required to quarantine—if this is your situation, use a home/antigen test.

WHERE to get a test:

  • The County continues to test individuals at its various mass testing sites and clinics. Visit sccfreetest.org. There are also tests through the Mountain View Los Altos High School District (choose the “freestyle” option as your school/organization), or El Camino Hospital.
  • Home antigen tests are a valuable tool. Starting Jan. 15, health insurers nationwide are required to cover the costs of up to eight at-home COVID tests per month. A positive result on an antigen test should be considered final; an additional PCR test should not be done. Home antigen tests are available through pharmacies, various retail stores as well as online vendors.
  • Large healthcare providers are legally required to provide prompt testing to patients who are symptomatic or have been exposed to someone who has COVID. 


  • Assume you have COVID and follow isolation guidelines. If members of your household are having similar symptoms, and at least one of them tests positive for COVID, assume that all members have COVID.
  • If you are having difficulty breathing or other severe symptoms, seek medical attention immediately.
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