Nicola Sturgeon has voiced “very serious concerns” about an apparent backlog of coronavirus test results.
The Scottish first minister said she was seeking “urgent discussions” with UK ministers over delays to results.
Only 70 new positive cases of the virus were confirmed in Scotland on Monday, compared to 244 on Sunday.
Ms Sturgeon said the figures were “not yet complete”, and suggested that schools going back in England could be causing a spike in demand for tests.
The system in Scotland was hit by “exceptional demand” when pupils returned to schools in August.
The Department of Health and Social Care (DHSC) said a “significant” number of people had been seeking tests, including some “who do not have symptoms and are not otherwise eligible” – but that capacity was at its highest level ever.
The “vast bulk” of Scotland’s coronavirus testing is carried out as part of a UK-wide network of test centres and mobile testing units, with the results processed in Lighthouse labs such as the one in Glasgow.
Ms Sturgeon said the Scottish government had been “fully engaged and involved in that system”, and wanted to work “in partnership with the UK government” to solve any problems.
However, amid reports of a backlog of tests, she said UK ministers needed to “share the scale and nature of the issues” so that “we can collectively and very quickly find solutions”.
Ms Sturgeon said: “We now have a very serious concern that the backlog of test results being faced by the UK lab network is starting to impact on the timeous reporting of Scottish results.
“We have reason to be concerned that the figures that have been reported today are not complete, because some of the turnaround of the tests done in Scotland over yesterday is longer.
“I’ll be seeking urgent discussions later today with UK government counterparts just to make sure we are doing everything possible to get on top of this before it becomes a bigger issue.”
On Sunday, the DHSC said the Test and Trace system was working and that “our capacity is the highest it has ever been”.
However, it added: “We are seeing a significant demand for tests, including from people who do not have symptoms and are not otherwise eligible.
“New booking slots and home testing kits are made available daily for those who need them and we are targeting testing capacity at the areas that need it most, including those where there is an outbreak, and prioritising at-risk groups.
“Our laboratories are processing more than a million tests a week and we recently announced new facilities and technology to process results even faster.”
At her daily coronavirus briefing, the first minister said Scotland was in a “precarious situation”.
Even with a lower number of positive results on Monday, they still represented 2.7% of people tested. A few weeks ago that figure was usually around or below 1%.
Ms Sturgeon said the number of new cases was trebling roughly every three weeks, a pattern which is “not sustainable”.
New restrictions on the number of people who can meet up were imposed on Monday, limiting gatherings to six people from two households.
Ms Sturgeon said: “We have to act now, we have to act quickly to prevent and even greater increase in cases as we go through autumn and into winter.”