Patients with high blood pressure admitted to hospital with coronavirus infections are twice as likely to die as those without the condition, researchers said on Friday.

For in-patients with the virus who had stopped taking medication for high blood pressure, the risk of dying doubled again, they reported in the European Heart Journal.

"It is important that patients with high blood pressure realise that they are at increased risk of dying from COVID-19," said senior author Fei Li, a cardiologist at Xijing Hospital in Xian, China. 

For the study, researchers in China and Ireland retroactively examined cases admitted to Huoshenshan Hospital in Wuhan between February 5 and March 15.

Nearly 30 percent -- 850 patients -- had a history of hypertension, another term for high blood pressure.

Four percent of those patients died, compared with just over one percent of the 2,027 patients without hypertension. 

After adjusting for age, sex and other medical conditions, the researchers calculated that having high blood pressure increased the risk of dying two-fold. 

In a separate meta-analysis of three other studies covering 2,300 COVID-19 patients from the same hospital, the researchers investigated the impact of different blood pressure drugs on death rates.

Contrary to their expectations, they found that a class of drugs known as RAAS inhibitors -- which include angiotensin-converting enzyme inhibitors (ACE) and angiotensin receptor blockers (ARB) -- were not linked to higher COVID-19 mortality.

Indeed, the risk appeared to be somewhat diminished.

"We suggest that patients should not discontinue or change their usual anti-hypertensive treatment unless instructed by a physician," said co-author Ling Tao, a professor at Xijing Hospital.

The authors noted that their study was observational and not based on clinical trials, meaning further research was needed before they could make firm clinical recommendations.