Almost 90 percent of COVID-19 patients who were placed on ventilators in New York’s largest hospital system have died from the coronavirus, according to a study.

Overall, 88 percent of the patients treated at Northwell Health died after receiving mechanical ventilation, Dr. Safiya Richardson at the Feinstein Institutes for Medical Research and her colleagues found.

Of the 2,634 patients whose outcomes were known, 14 percent were treated in the intensive care unit, 12 percent were placed on ventilators and 3 percent received kidney replacement therapy, the study said.

Twenty-one percent of the total group died, according to the findings, which were was published in the Journal of the American Medical Association.

The researchers studied the electronic health records of 5,700 patients with coronavirus disease hospitalized at Northwell Health, whose network includes Lenox Hill on the Upper East Side, LIJ in Forest Hills and New Hyde Park, and the Staten Island University medical facilities.

The findings supported doctors’ conclusions that people who become severely ill with COVID-19 frequently have underlying medical issues.

More than half, or 57 percent, had high blood pressure, 41 percent were obese and 34 percent suffered from diabetes, according to the study.

“Of the patients who died, those with diabetes were more likely to have received invasive mechanical ventilation or care in the ICU compared with those who did not have diabetes,” the researchers wrote.

The study also confirmed that men are more likely to die of the disease than women.

During triage, about a third of all the patients, or 1,734, had a fever, about 17 percent had a high respiratory rate and just under 30 percent needed supplemental oxygen.

On average, the patients were discharged after four days.

“This study reported mortality rates only for patients with definite outcomes (discharge or death), and a longer-term study may find different mortality rates as different segments of the population are infected,” the researchers wrote.

The Feinstein Institutes for Medical Research is the research arm of Northwell Health.