The American Journal of Medicine seems to disagree:

Does coverage affect medical outcomes?

There is an association among health insurance coverage, access to health care, and patient outcomes. Although 57% of the public reported they believe that those without health insurance are able to get the care they need, one survey found that the uninsured were less than half as likely as those with insurance to receive medical care for a serious medical condition, as judged by physicians.
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The most important prerequisite for access to care is health insurance coverage. Without it, most people cannot afford medical care. They are more likely to postpone or go without necessary treatment for fear of high medical bills.
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In fact, uninsured adults are at least four times as likely as the insured to report delaying or foregoing needed health services.
Growing evidence from large observational studies reveals the staggering effects of insurance status on general health outcomes. The uninsured poor, for example, are more likely to delay hospitalization compared with those with private health insurance, and when in the hospital, uninsured patients stay longer and experience higher death rates. In addition, hospitalized uninsured patients are 2.3 times more likely than those with insurance to have adverse iatrogenic events.
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Uninsured patients are twice as likely to die over 15 years compared with insured patients (18.4% vs 9.6%); even after adjusting for major health risk factors, mortality remains 25% higher among the uninsured.
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The effects of poor access to care for the uninsured are particularly striking for diseases which require early detection. The uninsured receive fewer preventive services such as blood pressure checks, mammograms, and screening for colorectal cancer.
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For example, the loss of Medicaid coverage has been associated with a 10-point increase in diastolic blood pressure and a 15% increase in the hemoglobin A1C in diabetic patients. This has translated into a higher probability of death over 6 months.
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In addition, because regular preventive care is not received, the uninsured are more likely to be diagnosed at advanced stages of cancer. Greater than 40% of uninsured women are more likely to be diagnosed with late-stage breast cancer, and 40% to 50% are more likely to die of breast cancer, compared with insured women, depending on their age.
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In the case of acute care, outcomes are consistently worse for uninsured patients. Among patients with appendicitis, for example, uninsured individuals were 1.5 times more likely than insured patients to present with an appediceal rupture.
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Conclusion

The problem of the uninsured in the United States is rapidly becoming a crisis, affecting a broader cross-section of society with each passing year. Growth in the numbers of uninsured Americans has continued annually for over the past decade, and currently more than 17% of the nonelderly population are uninsured. The poor and members of certain minority groups have historically been excluded by a system of voluntary health insurance in the United States. However, contrary to public perception, most Americans without health insurance today are members of working families and are U.S. citizens. The crisis of the uninsured has increasingly become a problem that reaches all racial, ethnic, and socioeconomic groups, and across a wide spectrum of occupations. Despite recent attempts to improve pediatric insurance coverage, children remain 20% of the total uninsured population.
The uninsured are battling both the decreasing affordability and availability of private health insurance, as well as the increasing restrictions on public health insurance programs. Despite an improved economy, obtaining low-cost health care when needed is becoming more difficult for the uninsured. Fewer employers cover their workers because of the increasing cost of health care, and fewer people can afford to pay. The high cost of private insurance plans themselves clearly affects access to medical services in that fewer people can afford health insurance. In addition, the increasing level of out-of-pocket costs for premiums and co-pays reduces usage of health care services.
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Governmental reforms to increase private and public health insurance have made little impact, and in some cases have made the problem worse. Thus, the gap between the increasing cost of health care and the reduced purchasing power of those trying to access health care seems to be the biggest factor in this national crisis.
Furthermore, the uninsured are more likely to have poorer health outcomes than those with health insurance. The high cost of care causes many uninsured people to postpone or forego necessary treatment. As a group, the uninsured are having their diseases detected later, and their morbidity and mortality are higher.
Whether or not one has health insurance affects job decisions, financial security, access to care, and health status. But lack of insurance and gaps in coverage affect all of society. When an uninsured person goes to a public hospital or clinic, an emergency department, or a private physician for care and cannot pay the full cost, some of the bill is passed on to those who do pay, through higher insurance premiums and in the form of taxes supporting our public medical insurance programs. We all pay for having a large and growing uninsured population.
Americans have boasted for years that we have the best health care in the world, but if this is true, it is the case only for those with health insurance. In fact, the clear relationship between insurance status and health outcomes should be considered a national emergency. If access to medical care and health care coverage correlates with improved clinical outcomes, where is the cry from the medical profession to increase both of these? If doctors are entrusted with improving the health care of our patients, we must be at the forefront of moving legislation toward increasing the coverage of all our citizens, thereby increasing the overall health of our nation.
https://www.amjmed.com/article/S0002...756-4/fulltext