Screening for loss of smell and taste was started by a health trust two months before the government officially accepted them as coronavirus symptoms.
Newcastle Hospitals NHS Trust director of infection prevention and control Lucía Pareja Cebrián said the screening helped identify more positive cases.
The symptoms were added to the official list of coronavirus signs on Monday.
The Department for Health said it kept "the evidence of Covid-19 symptoms under continuous review".
Dr Pareja Cebrián said reports from clinicians in Italy, Spain and locally prompted the inclusion of taste and smell loss in its screening of staff, staff households and patients in early March.
About a third of people swabbed had presented with the symptoms and those mostly tested positive for Covid-19, she said.
"It's very specific so, when you have it, the likelihood is very high, but not everyone presents with loss of smell," she said.
Loss of smell however, is rarely the only symptom and usually comes with a fever, fatigue or coughing.
But if someone presents with both, "then your suspicion is going to be higher", Dr Pareja Cebrián said.
Prior to the change in advice people using NHS 111 were only asked to self-isolate if they had a fever or cough, not if they had lost their sense of taste or smell.
"Loss of smell has been known about among clinicians for a long time," Dr Pareja Cebrián said.
"You catch more people by including loss of smell or taste in your screening questions."
Government advisors have been considering calls from doctors and scientific advisers to expand the list of symptoms.
Deputy Chief Medical Officer Prof Jonathan Van Tam said it had been a question of "which of these symptoms actually make the interception of cases better or worse".
Analysis had been needed before government scientists concluded there was a benefit to the addition, he said.