Maria, a 47-year-old middle school teacher, waited six weeks for approval on a procedure her cardiologist called urgent — only to receive a one-page denial letter citing “lack of medical necessity.” If you have ever held a letter like that in your hands, you know exactly how she felt.

Here is what most people do not realize: according to a 2023 report from the Kaiser Family Foundation, nearly 49% of in-network insurance claims are denied at the first submission across many major marketplace plans. Nearly half. That number stopped me cold when I first read it during my research years, because it means the system is not occasionally failing patients — it is routinely failing them.

So why is this happening, and more importantly, what can you do to be on the right side of that statistic?

The Number That Changes How You See Healthcare

When I tell people that nearly half of all claims get denied initially, the reaction is almost always the same: disbelief, then anger, then a quiet, unsettling question — has this happened to me without me knowing?

The answer, for millions of Americans, is yes.

Research shows that in 2022 alone, insurers on the federal marketplace denied approximately 17 million claims, according to the same Kaiser Family Foundation analysis of insurer data submitted to the Centers for Medicare & Medicaid Services. What is more striking is that only 0.1% of patients formally appealed those denials — meaning 99.9% of people either paid out of pocket, went without care, or simply gave up.

You are not alone in this. But the silence around it is part of the problem.

Why Insurers Deny Claims: The Clinical Reality

Did You Know: Insurance companies are legally required to provide a specific reason for every denial. If your letter is vague or uses generic language like “not medically necessary,” you have the right to request a detailed written explanation under the Affordable Care Act.

There are several documented reasons claims are denied, and understanding them is your first real line of defense.

1. Prior Authorization Failures Prior authorization — the requirement that your doctor get insurer approval before providing a service — is the leading driver of denials. A 2022 survey by the American Medical Association found that 94% of physicians reported prior authorization causing delays in patient care, and 33% said it had led to a serious adverse event for a patient in their care. That is not a bureaucratic inconvenience. That is a clinical crisis.

2. Coding Errors Medical billing uses something called ICD-10 codes — a standardized numerical language that tells insurers what diagnosis or procedure occurred. A single wrong digit can trigger an automatic denial. In my years of research, the pattern I kept seeing was that a significant percentage of denials had nothing to do with whether care was appropriate — it came down to paperwork. A 2020 study published in the Journal of the American Medical Association estimated that administrative complexity, including coding errors, costs the U.S. healthcare system over $265 billion annually.

3. Out-of-Network Confusion Patients often believe a hospital is in-network when, in fact, individual physicians working inside that hospital — anesthesiologists, radiologists, pathologists — operate under separate contracts. You can be treated at an in-network facility and still receive an out-of-network bill.

4. “Medical Necessity” Determinations This is where things get most troubling. Insurers employ their own medical reviewers who may determine a treatment is not “medically necessary” — even when your physician has documented exactly why it is. The science is actually fascinating here, and not in a comforting way: a 2021 report by the U.S. Department of Health and Human Services found that Medicare Advantage plans denied millions of claims that met Medicare coverage rules, suggesting the “medical necessity” filter is sometimes applied inconsistently at best.

Warning: Never ignore a denial letter. You typically have between 30 and 180 days to file an appeal, depending on your plan type. Missing that window permanently forecloses your right to contest the decision.

What Doctors Wish You Knew Before You File

What most doctors do not tell you — often because they are exhausted by the system themselves — is that how your care is documented before the claim is filed can determine whether it is approved.

Here is what physicians who deal with insurance regularly say matters most:

  • Ask your doctor to document medical necessity explicitly. Do not assume it is implied. Ask: “Will this be documented clearly enough for insurance purposes?”
  • Request a letter of medical necessity for any procedure that is elective-sounding but clinically required. Conditions like sleep apnea, certain mental health treatments, and weight-related interventions are frequently denied without one.
  • Know your plan’s formulary and coverage tiers before scheduling anything. This takes 20 minutes and can save you thousands.
  • Keep your own records. Request visit summaries, lab results, and referral letters. If a claim is denied, you will need this paper trail.

The cortisol (your body’s stress hormone) burden of navigating a denial when you are already sick or scared is real. Preparation is not pessimism — it is self-protection.

Pro Tip: If your claim is denied, ask your doctor’s office to file a Peer-to-Peer Review — a direct call between your physician and the insurer’s medical reviewer. Studies suggest this process overturns denials in a significant number of cases, yet most patients never know it exists.

Try This Today

Before your next medical appointment or procedure, do this:

  1. Call the member services number on the back of your insurance card and ask: “Does this specific procedure or service require prior authorization, and what documentation does my doctor need to provide?”
  2. Write down the name of the representative, the date, and what they told you. This record matters if there is a dispute later.
  3. Ask your doctor’s office: “Has this type of claim been denied by my insurer before, and if so, what did you do to overturn it?”

That single conversation — 10 minutes before care is delivered — is the most powerful thing you can do to protect yourself.

Action Step: If you have already received a denial, go to Healthcare.gov or your state’s insurance commissioner website and search for your plan’s external appeal process. Every ACA-compliant plan is required to offer an independent external review. Use it.

The Hidden Toll on Your Health

Here is the part that does not get enough attention: the chronic stress of fighting insurance denials — the phone calls, the paperwork, the waiting — activates your hypothalamic-pituitary-adrenal axis (the hormonal stress-response system in your brain and body) in the same way ongoing physical threat does. Research from the American Psychological Association shows that healthcare-related financial stress is one of the top drivers of chronic inflammation, sleep disruption, and anxiety in American adults.

Avoiding care because you fear denial is not a neutral choice. It is a health outcome in itself. And it is one the system is currently designed, whether intentionally or not, to produce.

Does that make you angry? It should. But anger, directed well, is useful.

Your Next 3 Steps

Step 1: Audit your last 12 months. Pull your Explanation of Benefits (EOB) statements — available through your insurer’s patient portal — and look for any denied or adjusted claims. You may have overpaid without realizing it. Federal law gives you the right to appeal claims retroactively within certain windows.

Step 2: Build a claim file for any upcoming care. Create a simple folder — digital or paper — with your referral letters, prior authorization numbers, physician notes, and insurer confirmations before your procedure date. If a denial comes, you will be ready.

Step 3: Find a patient advocate. Hospitals are legally required to have a Patient Advocate or Patient Representative on staff. This person’s entire job is to help you navigate billing disputes and appeals — for free. Most patients never ask for them. Ask.

The healthcare system is genuinely difficult to navigate, and I will not pretend otherwise. But the patients who come out on the right side of that 49% statistic are not lucky. They are prepared. And now, so are you.