The UK government’s new target of testing 200,000 people a day for Covid-19 is a source of “real frustration”, according to a leading scientist.
The president of the Institute of Biomedical Science (IBMS), said knowing where, how and how often people will be tested is more vital than goal setting.
IBMS president Allan Wilson also warned testing labs face a “hand to mouth existence”.
The prime minister has pledged to reach the new target by the end of May.
And Boris Johnson said after hitting the 200,000 target his aim is to “go even higher”.
It comes after health secretary Matt Hancock last week said 122,000 coronavirus tests were carried out on the final day of April, passing the government’s target.
But since then the government has failed to reach that daily landmark and Mr Wilson said the focus on numbers is not helpful.
He told BBC Radio’s Good Morning Scotland: “Given the fact that there was so much turmoil around the initial target of 100,000, to double that target, all it does is put pressure on the laboratories when it is really not required.
“What we need is a much more targeted approach to how we are going to reduce transmission of this disease and reduce deaths rather than another arbitrary politically-set target.”
Mr Wilson also claimed his members often find out about the latest goals from watching the news.
He added: “There is very little discussion with the laboratory service before these targets are increased and that’s a real frustration on staff who are under incredible pressure to deliver in this challenging time.”
The IBMS president said it is better to target people under the test, trace and isolate strategy, such as key workers, than concentrating on the numbers alone.
He also stressed testing should be done locally following reports carers with Covid-19 symptoms were told to drive hundreds of miles to get tested.
He added: “What we don’t seem to be able to do is join up the people who need to be tested with the testing and I think that is something we haven’t done well.”
First Minister Nicola Sturgeon last week said Scotland now has capacity to carry out 4,350 Covid-19 tests a day in NHS laboratories.
The Scottish government had previously set a target of 3,500 NHS tests a day by the end of April.
Mr Wilson described those numbers as “more realistic” but added that testing everyone was unlikely to be possible in the short to medium term.
He said: “It’s still in parts of the country – including Scotland – a bit of a hand-to-mouth existence for testing.
“We get deliveries of reagents and chemicals to do testing for a period of time, but we have no guarantee that there is a next delivery coming behind that so we can maintain that capacity.”
The IBMS is the leading professional body for scientists, support staff and students in the field of biomedical science and has more than 20,000 members in 61 countries.
Last month testing was expanded in England to millions more people with symptoms including over-65s, those who have to leave home to work, and people living with someone in these groups.
In Scotland, the first minister announced testing would be expanded to over-65s with symptoms and also all those in care homes where there had been an outbreak.
And last week, the Welsh government extended coronavirus testing to people in care homes even if they are not showing symptoms of the disease.
The UK government is hoping the enhanced testing regime, alongside contact tracing and continued social distancing, can stay on top of transmission rates and prevent a second wave of infection.
The prime minister will address the nation on a potential easing of the lockdown measures on Sunday.