Q&A on COVID-19 tests: What are they? Who should get one and how to get one.

Here’s the scoop on two types of widely available methods

After major shortages and glacial delays, two types of COVID-19 tests are becoming more widely available at hospitals, clinics, and academic, commercial and public health laboratories across California.

They detect different aspects of the disease.

One type of test tells you: Do you have the virus now?

The other type tells you: Did you have the virus in the past?

While testing guidelines and technology are constantly evolving, here’s what you need to know about COVID-19 tests.

What are PCR tests?

These tests detect if someone is actively infected with the coronavirus.

How do PCR tests work?

They typically involve a swab sample from the nose or throat and detection of genetic material from the coronavirus. Because the test requires the presence of the virus, it is most accurate in the first few days after infection.

How reliable are PCR tests?

These tests are generally very reliable. But it’s possible that a test result may come back negative due to problems with swab sampling. Perhaps the sample didn’t get enough material, or it wasn’t taken within the first few days after infection.

Who should get a PCR test?

People actively showing symptoms of COVID-19, such as coughing, fever or shortness of breath, should contact their medical providers or local resources to see if they should get tested.

State guidelines are constantly evolving, but the latest recommendations also include people without symptoms, such as health care workers, social service employees, essential workers, and residents and employees of congregate living facilities.

On Thursday, Contra Costa became the first county in the Bay Area to offer testing to anyone — even those without symptoms. Appointments will be given to

any county residents who believe they need a test, regardless of insurance or ability to pay.

Where can I get a PCR test?

Tests are provided in a variety of locations, including hospitals, public health labs, academic labs, businesses and a variety of other public locations that vary by city.

State officials have launched a new interactive website to help Californians find COVID-19 community testing sites near them. Go to covid19.ca.gov/ and scroll down to “Get testing and treatment.”

This site allows you to quickly search for testing sites by current location, address, city or zip code and schedule an appointment. It features community testing locations, including sites operated by Verily and OptumServe, which are open to Californians who meet current testing guidelines. Testing is free.

Detailed test location information is also available from your local county health department.

What are antibody tests?

These tests detect if someone was previously infected with the coronavirus.

How do antibody tests work?

They require a blood sample to detect antibodies to the coronavirus. Because it takes time for the immune system to generate antibodies, these tests are most accurate weeks after infection.

How reliable are antibody tests?

The performance of commercial antibody tests varies greatly. To address these issues, the Food and Drug Administration revised its guidance for antibody test manufacturers last week to raise validation and accuracy standards.

Who should get an antibody test?

This test is primarily for public health surveillance and research to understand the coronavirus spread. While a positive result indicates that antibodies were produced in response to a past infection, researchers are still learning whether these antibodies provide future immunity — and if so, for how long.

Bay Area counties vary in their recommendations. Contra Costa County does not recommend these tests for the general public at this time.

Santa Clara County also says these tests are most useful for research, rather than individual patients. Research studies are underway, including one in the San Francisco Bay Area funded by the Chan Zuckerberg Initiative.

Where can I get an antibody test?

Outside of the research setting, an increasing number of commercial labs are selling tests.

But because of performance problems, it’s buyer beware.

The FDA is only “authorizing” the sale of these tests; it hasn’t yet “approved” them through rigorous review.

For instance, Quest Diagnostics is selling antibody tests online at GetQuestTest.com. Consumers can also get a Quest test at some local Safeways, although an appointment and a physician’s referral are required.