The growing measles outbreak in Clark County has prompted an increase in residents seeking to be tested for immunity to the virus, with multiple local blood test labs and clinics reporting substantial increases in the number of tests performed in recent weeks.

The Vancouver Clinic has seen a more than tenfold increase in testing requests across its four urgent care locations in Clark County, according to marketing director Chastell Ely.

“Typically we’re averaging between 20 and 50 tests per month,” she said on Friday. “So far in January, we’ve done 500-plus.”

The procedure, known as a titer test, analyses a patient’s blood sample to detect the presence of the specific antibodies needed to fight off infections. Some versions screen only for measles resistance, while others combine it with a test for resistance to mumps and rubella, similar to how the MMR vaccination targets all three viruses.

“We’ve seen a dramatic increase in testing for immunity, starting around last Thursday,” said Eileen Morton, lab manager at the Fourth Plain Boulevard branch of the company Any Lab Test Now, which offers quick $50 immunity tests for measles alone, with results usually available the following day.