Insurance Denied Blood Work? How to Appeal

Your doctor ordered a lab test. Your insurer denied it as "not medically necessary." Now you're stuck holding a denial letter that seems to say your doctor was wrong — but your doctor stands behind the order. This situation is more common than most patients realize, and the denial does not have to be the final word. This article walks you through exactly why these denials happen, what documentation you need, and the specific steps — including a powerful tool called peer-to-peer review — that overturn a significant share of them.

What "Not Medically Necessary" Actually Means

A medical necessity denial does not mean your insurer thinks your doctor is incompetent or that the test was clinically wrong. It means the documentation submitted with the claim did not satisfy the insurer's internal coverage criteria for that specific test. Those are very different things, and understanding the difference is the foundation of a successful appeal.

Insurers use proprietary clinical criteria systems — most commonly products called InterQual (owned by Change Healthcare) or MCG Guidelines (formerly Milliman Care Guidelines) — to evaluate whether a service qualifies for coverage. These criteria establish specific conditions that must be documented: a particular diagnosis code, a prior failed treatment, a specific symptom duration, or a combination of lab values. If the claim or prior authorization request didn't include language that checked those specific boxes, the system flags it as not meeting criteria — even if your doctor's clinical reasoning is sound and consistent with published medical guidelines.

In short: insurers are often evaluating paperwork against a checklist, not second-guessing your physician's judgment. That distinction matters because it tells you exactly where to focus your appeal.

Start Here: Request a Peer-to-Peer Review

Before filing a formal written appeal, ask your doctor's office to request a peer-to-peer review. This is the single most effective first step for medical necessity denials, and it costs you nothing.

A peer-to-peer review is a direct phone call between your treating physician and the insurer's medical director — the physician employed by the insurance company who made or supervised the denial decision. Your doctor explains the clinical rationale in their own words, can reference your specific history and symptoms, and can address the insurer's criteria directly. This conversation happens outside the paperwork process and bypasses many of the documentation gaps that triggered the denial in the first place.

Peer-to-peer reviews overturn a substantial percentage of medical necessity denials. Exact rates vary by insurer and test type, but physician advocacy organizations consistently report reversal rates ranging from 30% to over 70% in some specialties following peer-to-peer calls.

How to Request a Peer-to-Peer Review

1. Call the member services number on the back of your insurance card and ask specifically: "How do I arrange a peer-to-peer review for a medical necessity denial?"
2. Get the name, phone number, and any scheduling window for the insurer's medical director or clinical reviewer handling your case.
3. Bring that information to your doctor's office and ask them to initiate the call. Most physician offices are familiar with this process — it is standard practice.
4. Ask the office to document the call date, the reviewer's name, and the outcome in writing, whether the denial is reversed or upheld.

If the peer-to-peer review resolves the denial, you're done. If it doesn't — or if the insurer refuses to schedule one — move to a formal internal appeal.

Filing a Formal Internal Appeal

Every insurer is required by federal law to have an internal appeals process. Under the Affordable Care Act (ACA), you have the right to a full and fair review of any adverse benefit determination. You typically have 180 days from the date of the denial notice to file an internal appeal, though checking your specific plan documents for the exact deadline is important.

A strong internal appeal for a medical necessity denial requires three specific documents working together.

1. A Letter of Medical Necessity That Addresses the Denial Reason Directly

A letter of medical necessity (sometimes called an LMN) is a letter from your treating physician explaining why the test is required for your care. The critical detail: the letter must respond specifically to the reason stated in your denial letter, not just explain why the test is a good idea generally.

If the denial says the test does not meet criteria because there is no documented prior conservative treatment, the letter must address that — either explaining that prior treatment was attempted and documenting it, or citing a clinical reason why skipping that step is medically appropriate in your specific case. Generic letters that don't engage with the stated denial reason are often rejected on appeal without meaningful review.

2. The Insurer's Clinical Criteria Document

You have the legal right to request the specific clinical criteria the insurer used to deny your claim. Call member services and ask for "the clinical coverage criteria or InterQual/MCG criteria used to evaluate this denial." They are required to provide it.

Once you have this document, read it alongside your denial letter. Look for the exact conditions listed as required for coverage. Your appeal — and the letter from your doctor — should address each criterion by name, either confirming it is met and providing documentation, or explaining why an exception applies.

3. Published Clinical Guidelines Supporting the Test

Gather published guidelines from recognized medical organizations that support ordering the test under your circumstances. Relevant sources include:

• The U.S. Preventive Services Task Force (USPSTF) at uspreventiveservicestaskforce.org
• Specialty society guidelines (American Diabetes Association, American Heart Association, American College of Gastroenterology, and others relevant to your condition)
• The American Medical Association (AMA) clinical practice guidelines

If published guidelines from a recognized body recommend this test for patients with your diagnosis and presentation, include those pages in your appeal. Insurers are required under the ACA to take recognized clinical guidelines into account.

A Concrete Example

Suppose your doctor orders a HbA1c blood test (a measure of average blood sugar over three months) and the insurer denies it for a patient with a documented prediabetes diagnosis, citing that the test was performed less than 90 days after a prior result. The denial cites internal criteria requiring a 90-day interval between tests.

Your appeal package would include: (1) a letter from your doctor explaining that you had a significant weight change or started a new medication affecting glucose levels since the last test, making early retesting clinically appropriate; (2) the insurer's criteria document confirming the 90-day rule and any exceptions listed; and (3) the American Diabetes Association's Standards of Medical Care, which states that more frequent testing is appropriate when treatment changes or clinical status warrants reassessment. That three-part package directly engages the denial reason, provides a clinical basis for an exception, and cites a recognized authority. That is what a successful appeal looks like.

For more on the general appeals process, see our guide on how to appeal a denied insurance claim.

If the Internal Appeal Fails: External Independent Review

If your internal appeal is denied, you are not out of options. Under the ACA, you have the right to request an external review — a review by an independent physician or review organization that has no affiliation with your insurance company. This right applies to most medical necessity denials for people in employer-sponsored plans, marketplace plans, and many other regulated plans.

External review is free to you. The independent reviewer — not your insurer — makes the final binding determination. If the external reviewer overturns the denial, your insurer must cover the service.

External review overturn rates for diagnostic and laboratory test denials are meaningful. Studies of state external review programs have found that consumers win roughly 40% to 60% of external reviews they pursue, depending on the state and type of denial — making it well worth pursuing when an internal appeal fails.

How to Request External Review

1. Your denial letter for a final internal appeal decision must include instructions for requesting external review — federal law requires this language.
2. For most employer-sponsored plans, external review is handled through a federally-contracted independent review organization (IRO). For state-regulated individual and small group plans, your state insurance commissioner oversees the process.
3. You generally have 4 months from the date of the final internal appeal denial to request external review.
4. Submit the same documentation package you used for the internal appeal, plus any additional clinical records your doctor can provide.

The CMS External Review Process and your rights under the ACA are described in detail at the sources linked below. If you're unsure whether your plan is subject to federal or state external review rules, call your state insurance commissioner's office — they can tell you which process applies.

If your situation involves a prior authorization denial rather than a claim denial, the same appeal rights generally apply — our article on what prior authorization is and how to fight denials covers that process in detail.

What to Do Right Now

If you have a medical necessity denial for a lab test or blood work in hand, take these steps in order:

1. Call your insurer today and ask how to arrange a peer-to-peer review. Get the scheduling details and bring them to your doctor's office.
2. Request the clinical criteria document used to deny your claim — you have the right to it.
3. Ask your doctor's office to prepare a letter of medical necessity that responds specifically to the denial reason, not a generic template.
4. File a formal internal appeal with that letter, the criteria document, and relevant clinical guidelines before your deadline (check your denial letter for the date).
5. If the internal appeal fails, request external review immediately — it is free, binding on your insurer, and patients win a meaningful percentage of these cases.

You are not required to accept the first denial, the second denial, or even the internal appeal denial. The system has built-in checkpoints designed to catch errors. Using them is not adversarial — it is exactly what they are there for.

Sources: CMS External Review Process, ACA Internal Appeals and External Review Rules — Healthcare.gov