Medicare Part B covers a broad range of laboratory tests, from routine blood work to cancer screenings, as long as they are ordered by a doctor and considered medically necessary. For most covered lab tests, you pay nothing out of pocket. That $0 cost applies even though Part B normally requires a 20% coinsurance for other services. Lab tests are one of the few categories where Medicare waives both the annual deductible and coinsurance entirely.
What counts as “covered” depends on whether the test is diagnostic (ordered to investigate a symptom or monitor a condition) or preventive (a screening for people without symptoms). The rules differ for each.
Diagnostic Lab Tests: The Broad Category
Any clinical laboratory test that your doctor orders to diagnose or manage a medical condition is eligible for coverage under Part B. There is no fixed list of approved diagnostic tests. Instead, Medicare uses a medical necessity standard: if your doctor has a documented reason to order the test, and it relates to a specific health problem you’re being treated for, Medicare will generally pay for it.
This includes common blood panels like complete blood counts, metabolic panels, thyroid function tests, liver and kidney function tests, urinalysis, cultures for infections, and countless others. It also covers more specialized tests such as genetic panels when ordered to guide treatment decisions for a diagnosed condition. The key requirement is that a treating physician must order the test for a specific medical reason, and that reason must be documented in your medical record.
Your cost for these diagnostic lab tests is $0 when the lab accepts Medicare assignment, which most labs do. You do not pay the Part B deductible (currently $283 per year for 2026) for clinical laboratory services, and there is no coinsurance.
Preventive Screenings Medicare Covers
Beyond diagnostic testing, Medicare covers several preventive lab screenings at no cost to you, even if you have no symptoms. Each has its own eligibility rules and frequency limits.
Diabetes Screening
Part B covers up to two blood glucose screenings per year if your doctor determines you’re at risk. These can be fasting glucose tests, A1C tests, or other Medicare-approved glucose tests. You qualify if you have high blood pressure, a history of abnormal cholesterol or triglyceride levels, obesity, or a history of high blood sugar. You also qualify if two or more of the following apply: you’re 65 or older, you’re overweight, you have a family history of diabetes, or you have a history of gestational diabetes or delivering a baby weighing more than 9 pounds.
Colorectal Cancer Screening
Medicare covers several types of colorectal cancer screening lab tests, including fecal occult blood tests, multi-target stool DNA tests (the most well-known brand is Cologuard), and newer blood-based biomarker tests. The specific frequency and age requirements vary by test type, but these are covered as preventive services with no cost to you.
Prostate Cancer Screening
PSA (prostate-specific antigen) blood tests are covered once every 12 months for men 50 and older.
Hepatitis B and Hepatitis C Screening
Part B covers screening for hepatitis B virus infection and hepatitis C virus. Hepatitis C screening is particularly relevant because the CDC recommends it for all adults at least once, and Medicare follows that guidance.
HIV Screening
HIV blood tests are covered as a preventive benefit. Medicare covers screening for people at increased risk and for anyone who requests it.
Sexually Transmitted Infection Screening
Part B covers STI screenings and related counseling for people at increased risk.
For all of these preventive screenings, your cost is $0 when you see a provider who accepts Medicare.
When Medicare Won’t Pay for a Lab Test
Medicare will deny a lab test claim if it doesn’t meet the medical necessity standard. This usually happens in one of a few scenarios: the test wasn’t ordered by your treating physician, the diagnosis code on the order doesn’t match what Medicare considers a valid reason for that particular test, or the test is being repeated more frequently than Medicare allows.
Local Coverage Determinations (LCDs) play a big role here. These are region-specific rules that spell out which diagnosis codes justify which tests. A vitamin D level, for example, might be covered if you have osteoporosis or kidney disease but denied if ordered as part of a general wellness check without a qualifying diagnosis. The same test can be covered or denied depending on why your doctor ordered it.
Screening tests ordered outside the covered frequency are another common denial. If you had a diabetes screening three months ago and your doctor orders another one, Medicare may not pay for the second test within that 12-month window unless there’s a separate diagnostic reason.
What Happens When a Test Might Not Be Covered
When a lab or your doctor’s office believes Medicare is unlikely to pay for a specific test, they are required to give you a form called an Advance Beneficiary Notice of Noncoverage (ABN) before performing the test. This form lists the tests in question and explains that you may have to pay out of pocket.
You then choose one of three options. You can have the test done and ask the lab to bill Medicare anyway, so you get an official coverage decision you can appeal if it’s denied. You can have the test done but skip the Medicare claim entirely, accepting full financial responsibility. Or you can decline the test altogether, in which case you owe nothing.
If a lab runs a test that Medicare denies and they never gave you an ABN beforehand, the lab generally cannot bill you for it. This protection is important to know about. If you receive a surprise bill for a denied lab test and you never signed an ABN, you have grounds to dispute the charge.
Medicare Advantage and Lab Coverage
If you have a Medicare Advantage plan (Part C) rather than Original Medicare, your plan must cover at least the same lab tests that Original Medicare covers. Many Advantage plans cover additional services or have agreements with specific lab networks. Check with your plan to confirm which labs are in-network, because going out of network could mean higher costs even for tests that would be free under Original Medicare.
At-Home Test Kits
Medicare’s coverage of at-home test kits is limited. During the COVID-19 public health emergency, Medicare temporarily covered over-the-counter COVID tests, but that program ended on May 11, 2023. Standard laboratory-conducted COVID tests, like PCR tests ordered by a doctor and processed at a lab, are still covered.
At-home colorectal screening kits that involve mailing a sample to a lab (such as Cologuard) are covered when ordered by your doctor as part of the preventive screening benefit. The distinction is that these are physician-ordered tests processed by a certified lab, not truly over-the-counter products you buy on your own. General wellness test kits purchased directly by consumers without a doctor’s order are not covered.
How to Avoid Unexpected Lab Bills
Most surprise lab bills come down to one of three issues: the lab was out of network, the test lacked a qualifying diagnosis code, or the test exceeded Medicare’s frequency limits. A few practical steps can help you avoid these situations.
- Confirm the lab accepts Medicare assignment. When your doctor sends you to a lab, ask whether it’s a Medicare-participating lab. Major chains like Quest and Labcorp generally accept assignment, but smaller or hospital-based labs sometimes don’t.
- Ask your doctor about medical necessity. If your doctor is ordering a test and you’re unsure Medicare will cover it, ask whether the test is linked to a specific diagnosis. Routine “wellness panels” without a qualifying condition are a common source of denied claims.
- Watch for the ABN form. If someone hands you an ABN to sign, that’s a signal the test may not be covered. Read it carefully and make a deliberate choice rather than signing automatically.
- Track screening frequency. For preventive tests like diabetes or cancer screenings, keep a record of when you last had each one so you know whether you’re within the covered interval.