Police are warning pensioners to be on the alert for a new form of con trick, in which people posing as nurses take blood samples from their victims while stealing their money.

So far, four cases have come to light in Utrecht and Eindhoven.

Earlier this week, a 90-year-old Eindhoven man lost a large sum of money after thieves talked their way into his home saying they were testing people’s blood as part of an anti-flu campaign.

The man, who finds it difficult to walk, opened his door to a couple who said they were nurses and ‘overwhelmed’ him with a story about a flu epidemic which was particularly dangerous to the elderly, local broadcaster Omroep Brabant reported.

After being let into the house, the woman proceeded to take a sample of the man’s blood, while her partner checked around the house. After looking at the sample with a ‘testing instrument’ the female con artist told the man ‘it’s not great, but luckily we can order a pill for it’. The man was asked to use his bank card to pin the sum of one euro to pay.

The ‘nurses’ then headed for a nearby ATM and proceeded to empty the man’s account, Omroep Brabant said.

Police on Tuesday issued a warning about three similar cases in Utrecht, two of which involved two women in their early 20s who ‘spoke Dutch without an accent’ and who claimed to be nurses.

In all three Utrecht cases, which happened earlier this month, the thieves took blood samples from their victims and stole their bank cards.