A number of patients could be affected by disruption in the supply chain of tubes used in blood tests.

All clinically necessary blood tests will go ahead but others have been scaled back in light of a global supply chain issue.

Doctors have been told to only call for some tests under certain circumstances and patients with suspected allergies and vitamin D deficiencies could face delays to routine testing.

Fertility blood tests may also be affected.

NHS England issued guidance amid a global shortage of blood tube products.

It comes after medical technology company Becton Dickinson reported temporary supply chain issues for a number of tubes used to collect samples in blood tests.

The NHS guidance says GPs can “reduce non-essential (non-clinically urgent) testing”.

This includes stopping vitamin D testing except in exceptional circumstances and deferring routine infertility testing unless the patient is over the age of 35.

It also says allergy testing is “not a priority at this time” unless there is clinical need, and that routine wellness screening is “not a priority”.

The guidance also advises against stockpiling tubes.

Becton Dickinson has been contacted for comment.

A spokesperson for the Department of Health and Social Care said: “Patient safety and continuity of care is our priority and we are working to ensure there is minimal possible impact on patient care.

“The health and care system is working closely with BD to put mitigations in place to resolve any problems if they arise.”