The short answer: Your insurer wants to confirm that the MRI is medically necessary before it agrees to pay. MRI is expensive, and plans use prior authorization to check each order against clinical criteria for when imaging helps. Your doctor's office usually submits the request, not you. If the plan says no, you and your doctor can appeal, and in most cases you can ask for an independent external review.
What is prior authorization for an MRI?
HealthCare.gov defines preauthorization as a decision by your health plan that a service, treatment, drug, or equipment is medically necessary. It goes by other names too: prior authorization, prior approval, or precertification. The approval happens before you get the service.
The same definition has a catch. Preauthorization isn't a promise that your plan will cover the cost. An approved MRI still runs through your deductible, coinsurance, and network rules. Our guide to MRI costs without insurance covers the self-pay side, which is a separate question.
Not every plan requires approval for every MRI. Requirements differ by plan, body part, and reason for the scan. Your plan documents or the member services line can tell you which scans are on the list.
Why do insurers require it for advanced imaging?
The simple reason is cost control. The American Medical Association describes prior authorization as a health plan cost-control process that requires advance approval before a service qualifies for payment. MRI, CT, and PET scans cost far more than an X-ray or ultrasound, so they draw the most review.
The second reason is utilization management. Plans want to catch scans that are unlikely to change care, such as early imaging for routine back pain that often gets better on its own. They also want to steer patients to a cheaper test first when that test answers the question.
To make these calls, reviewers compare the order with appropriate-use criteria. The best known are the ACR Appropriateness Criteria, written by the American College of Radiology. The ACR describes them as evidence-based guidelines to help referring providers choose the most appropriate imaging test. The program includes 279 documents covering more than 4,100 clinical scenarios. More than 700 volunteer physicians on expert panels develop and review them each year.
Plans may use these criteria or their own versions of them. So the same knee, head, or spine MRI can pass at one plan and stall at another. If your doctor is weighing a different test, MRI vs CT scan explains what each one shows best.
Physicians dispute how well this works in practice. In the AMA's 2025 survey of 1,000 practicing physicians, 35% said prior authorization criteria are rarely or never evidence-based. The same survey found that 95% reported care delays linked to the process.
Who submits the request, you or your doctor?
The ordering provider submits it. That is the doctor, nurse practitioner, or physician assistant who ordered the scan, or their office staff. The request includes your diagnosis, your symptoms, how long they have lasted, what treatment you tried, and any earlier imaging.
The workload is heavy. The AMA's 2025 survey found that practices complete an average of 40 prior authorizations per physician each week. Physicians and their staff spend 13 hours a week on them.
Your part is smaller, but it still matters:
- Ask the office whether your plan needs approval for this scan.
- Give the office your current insurance card, especially if you changed plans.
- Ask the imaging center to confirm the approval number before your appointment.
- Check the dates on the approval, since many expire if the scan is not done in time.
How long does approval take?
It depends on your type of coverage. Many requests clear in a day or two. Deadlines set by law are the outer limit.
The CMS Interoperability and Prior Authorization final rule (CMS-0057-F), released January 17, 2024, set new limits for some plans. Starting January 1, 2026, Medicare Advantage plans, Medicaid, and CHIP must decide urgent requests within 72 hours. They must decide standard requests within 7 calendar days. KFF notes that the rule does not change the timeframes for Marketplace plans. It also does not apply to most employer plans.
Employer plans follow Department of Labor rules. The plan must decide a pre-service claim within a reasonable time and no more than 15 days. For urgent care, the limit is 72 hours.
Once the scan is done, the next wait is for the report. See how long it takes to get MRI results.
What can you do if the MRI is denied?
A denial is often not the final word. KFF found that Medicare Advantage insurers received nearly 53 million prior authorization requests in 2024 and denied 4.1 million, or 7.7%. Only 11.5% of denials were appealed. Of those appeals, 80.7% were partly or fully overturned.
The usual steps go in this order:
- Read the denial letter. Under CMS-0057-F, the plans it covers must give a specific reason for a denial. Missing records or a skipped step, like a trial of physical therapy, are common reasons.
- Ask for a peer-to-peer review. Many plans let your doctor talk directly with the plan's physician reviewer. Your doctor can explain details the paperwork missed.
- File an internal appeal. HealthCare.gov says you must file within 180 days of the denial notice. For a service you have not received yet, the plan must decide within 30 days. Urgent appeals move faster.
- Request an external review. An independent third party reviews the case, not the insurer.
If your symptoms change while you wait, tell your doctor. New symptoms can support a new request, and symptom.md can help you judge which ones need prompt care.
What rights do you have as a patient?
The key right is an outside review. According to HealthCare.gov, you can ask for an external review within 4 months of a final denial. A standard review must be decided within 45 days. An expedited review must be decided within 72 hours, or sooner if your health requires it. Your insurer is required by law to accept the reviewer's decision.
External review costs little. The federal process has no charge. Other processes may charge a fee, but no more than $25.
In an urgent situation, you do not have to wait for the internal appeal to end. You can file the internal appeal and the external review at the same time. Employer plans must give you at least 180 days to appeal a denied claim, per the Department of Labor.
Keep a written record of each call: the date, the name of the person, and any reference number. Ask for all decisions in writing.
The bottom line
Insurers require prior authorization for MRI because it is costly, and they want to confirm each scan meets criteria for medical necessity. Your doctor's office files the request. New federal rules set 7-day and 72-hour deadlines for Medicare Advantage, Medicaid, and CHIP, and employer plans have their own limits. If a scan is denied, ask for the reason, then appeal. Most appealed denials in Medicare Advantage are overturned.
Last updated: September 2026. This article is for informational purposes only and does not constitute medical or legal advice. Check your plan documents and talk with your doctor and your insurer about your specific coverage and appeal options.