The findings of the research, funded by the National Institute for Health Research (NIHR) and published today in BMJ Quality & Safety, were consistent for 18 common procedures performed between 2006 and 2019 on more than 3.5 million patients.
Since 2009, NHS patients in England have been able to choose where they want to be referred for non-urgent hospital treatment, and their choice can include independent sector hospitals.
The NHS spend on independent sector providers rose steadily from 3% in 2006-07 to 7.5% in 2015-2016, with the purchase of elective care one of the fastest growing areas of NHS expenditure on the independent sector.
But concerns have been raised as to whether NHS patients treated in the independent sector get the same standard of care as they would in an NHS hospital, particularly if complications arise in facilities without intensive care provision.
To explore these concerns further, the researchers drew on national Hospital Episode Statistics data for 18 common surgical procedures performed between 2006 and 2019.
The procedures included impacted wisdom tooth removal; gallbladder removal (cholecystectomy); prostate surgery (endoscopic resection); hysterectomy; hernia repair; nerve decompression of the lower (lumbar) spine; and hip and knee replacements.
The researchers compared length of hospital stay; emergency transfers to another hospital or death; and readmission or death within 28 days of discharge for each type of surgery.
In all, they compared 3,203,331 operations in 734 NHS hospitals and 468,259 operations in 274 independent sector hospitals. Most (393,086; 84%) procedures in the independent sector were carried out in for-profit organisations.
Patients treated in the independent sector were, on average, older. But they had fewer underlying conditions; lived in more affluent areas; and tended to be White (or had no ethnicity recorded) than those treated in NHS hospitals.
Nearly all patients were discharged alive within 60 days of admission, but patients in independent sector hospitals were more likely to be transferred to another hospital as an emergency, while inpatient death and non-emergency transfer were more likely for patients treated in NHS hospitals.
But the researchers found no strong evidence of a difference in overall rates among patients treated in either the public or private sector.
And length of stay was significantly longer for patients treated in NHS hospitals than it was for those treated in the independent sector for all 18 procedures included in the analysis.
Hip replacement patients spent 1.3-2.5 fewer days in hospital while those whose wisdom teeth had been removed were discharged home 30 minutes sooner, for example.
Nearly 40% of patients treated in independent sector hospitals were discharged on the same day after a total hip replacement, compared with less than 5% of patients treated in NHS hospitals, who stayed an average of 5 days.
Treatment in an independent sector hospital was also associated with a lower risk of emergency readmission. For example, following an operation for lumbar decompression, the risk of readmission for patients treated at an independent hospital was around a third of that for patients treated at an NHS hospital whereas for gallbladder removal the risk was three quarters of that at an NHS hospital.
This is an observational study, and as such, can’t establish cause, added to which the researchers were only able to evaluate a limited number of outcomes.
While many factors can influence the course of hospital treatment, the researchers speculate that “greater technical efficiency may explain some of the findings in our study”.
Professor Richard Lilford, of the University of Birmingham, said: “Plausible concerns have been expressed regarding the safety of elective surgery in the independent sector. Taken in the round, our findings provide a measure of reassurance that independent sector healthcare providers are providing an acceptable service.
“In the context of meeting the backlog of cases following the COVID-19 pandemic this may be a useful finding. But our results stop short of total reassurance, and ongoing scrutiny of a richer set of outcomes and further investigation of practice is required in both the NHS and the independent sector.”