GPs have called for more clarity over how long a shortage of blood test tubes will last as they face tough choices.
Doctors have been forced to stop all non-urgent testing after a shortage of vials, caused by Covid demands and transport issues.
The NHS in England and Wales has told doctors to temporarily halt some tests including those for fertility, allergies and pre-diabetes.
Supplier Becton Dickinson said it has experienced record demand for tubes over recent months, in part due to Covid patients.
The supplier has also been affected by transport issues including challenges at the UK border.
The shortage is likely to worsen over the next few weeks and could last until mid-September, NHS England said.
The government is working with suppliers while the NHS looks for alternative products.
“No doctor knowingly undertakes unnecessary blood tests and to now have to ration all those we are doing, as well as cancel hundreds more, goes against everything we stand for as clinicians,” the British Medical Association’s Dr David Wrigley said.