People who are being treated for kidney disease or high blood pressure should never use jacuzzis, doctors have warned.

It follows the case of a man in Germany who almost died after sitting in a tub.

The 36-year-old man, who had end-stage renal disease, suffered internal bleeding in one of his kidneys after spending time in the jacuzzi.

Whirlpools are a potential health risk for some patients Dr Lutz Liefeldt

Doctors believe pressure from the water caused the injury.

The man showed no signs of injury until after he underwent routine dialysis the following day.

By this point he was suffering severe abdominal pain, and vomiting. His blood pressure was also high.

Extensive tests

Doctors only picked up the source of the problem after extensive tests.

The patient was more vulnerable to the pressure from the water than most because he had cysts on his kidney which subsequently burst.

However, doctors at Charite University Hospital in Berlin said that patients with other types of kidney disease should also be warned of the dangers.

This is because they take anticoagulants as part of their dialysis treatment. These are drugs which prevent blood-clotting. They are also prescribed to people who have suffered blood clots.

Dr Lutz Liefeldt, one of the doctors involved in the case, said patients who take anticoagulants were at particular risk because if they suffered an injury they could lose a substantial amount of blood.

He also warned patients with high blood pressure to avoid jacuzzis.

"If a patient has high blood pressure, there is high blood pressure in their blood vessels throughout the body," he told BBC News Online.

"This means that even small injuries in blood vessels can produce substantial bleeding."

He added: "Whirlpools are a potential health risk for some patients."

The doctors highlighted the case in a letter to the medical journal The Lancet.

Many leisure centres already advise people with high blood pressure or pregnant women not to use jacuzzis.

They are also associated with skin infections or legionellosis if they are not regularly cleaned and the water properly chlorinated.

Some studies have suggested that jacuzzis could have health benefits for certain groups.

Researchers in the United States reported in 1999 that spending half an hour in a jacuzzi each day could help to control diabetes.