By the VerifyDoc team
If your pathology bill lists more line items than the number of separate tissue specimens your doctor sent to the lab, you may be looking at an overcharge — and the governing rule is clear: surgical pathology services are billed per separately submitted specimen, not per tissue block, not per slide, and not per jar.
This post walks through exactly how pathology billing is supposed to work, what the CMS National Correct Coding Initiative (NCCI) Policy Manual says about units of service, and how to spot the specific patterns that inflate a patient's share of the bill. We'll use a labeled illustrative scenario so you can see the logic applied to a real-world billing situation.
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Check my bill — free preview →What Is a "Specimen" vs. a "Block" — and Why It Matters to Your Bill
When tissue is removed during a biopsy or surgery, the sample goes to a pathology lab where technicians physically process it. They embed it in wax, slice it into thin sections, mount those sections on glass slides, and stain them so a pathologist can examine the tissue under a microscope. Each of those slices is called a tissue block. A single specimen — say, a colon polyp your gastroenterologist removed — might produce anywhere from one to ten or more blocks depending on its size and what the pathologist needs to see.
The critical billing rule: the number of blocks does not determine the number of billable units. Per the CMS NCCI Policy Manual, the unit of service for surgical pathology is the specimen: one specimen equals one billable unit. The number of slides, tissue blocks, or tissue fragments does not increase the unit count. NCCI defines a specimen as tissue submitted for individual and separate attention, examination, and diagnosis, and notes that separate specimens are usually submitted in separate containers.
This distinction matters because pathology charges can generate significant cost-sharing. Each unit of surgical pathology service is a separate billable charge, so an inflated unit count inflates every amount calculated from it. What one unit actually pays varies by payer, plan and locality, so read the amount off your own Explanation of Benefits rather than a typical figure. Multiply that by an inflated unit count — blocks instead of specimens — and a patient's coinsurance exposure climbs accordingly.
The Governing Rule: CMS NCCI Chapter 10
The authoritative source for how pathology services must be counted is the CMS National Correct Coding Initiative (NCCI) Policy Manual, Chapter 10, which covers Pathology and Laboratory Services (CPT codes 80000–89999). The guide reflects CMS NCCI Policy Manual Chapter 10 effective January 1, 2026. The NCCI program establishes what the government considers correct coding, and providers who bill contrary to it are subject to claim denial, audit, and repayment.
Under Medicare NCCI manual rules, providers cannot unbundle services. Unbundling in the pathology context means splitting one specimen examination into multiple billing units — for example, billing separately for each block taken from a single lumpectomy specimen. The most common pathology billing error is also the most expensive: unbundling. A general biller sees a requisition form with five line items, codes five units of the surgical pathology service, and the provider gets paid for five blocks — then Medicare audits 18 months later and recoups everything because those five blocks came from a single specimen.
For a concrete illustration: coders must count specimens, not containers and not blocks. One breast lumpectomy specimen equals one unit of surgical pathology service, regardless of whether the pathologist took ten blocks. That rule applies regardless of which hospital, lab, or outpatient facility performed the service. The CPT code assignment rules remain identical across settings — specimen type determines code level regardless of where the pathology service occurs.
Illustrative Scenario: A Colonoscopy with Four Biopsies
The following is a clearly illustrative hypothetical, not a real patient record. It is designed to show how the rules apply.
Imagine a patient — call her Maria — undergoes a routine colonoscopy. The gastroenterologist removes four polyps from different locations in the colon and sends each one to the lab in a separately labeled container, each logged as its own specimen. The pathologist examines each polyp and prepares a report. The lab bills four units of surgical pathology — one per specimen. That is correct billing.
Now imagine the pathologist needed to examine each polyp more closely and took three tissue blocks per polyp — twelve blocks total. If the lab billed twelve units instead of four, that would be an overcharge. The twelve blocks came from four specimens; only four units are billable. Surgical pathology services are billed once per separately submitted specimen, not per block or slide. This per-specimen logic drives most unit disputes.
When Maria receives her Explanation of Benefits (EOB) from her insurer and her itemized hospital bill, she should be able to cross-reference the number of pathology units billed against the pathology report, which lists each specimen (often labeled "Specimen A," "Specimen B," etc.). If the bill shows twelve pathology line items and the report shows four specimens, she has grounds to dispute. You can learn more about reading every line of your bill in our guide on Understand Your Itemized Hospital Bill: How to Read Every Line (2026).
Special Rule: Prostate Needle Biopsies Under Medicare
Prostate needle biopsies have their own distinct Medicare rule that goes even further than the general per-specimen standard. Per CMS NCCI Policy Manual Chapter 10 (effective January 1, 2026), surgical pathology for any and all prostate needle biopsy specimens from a single Medicare patient on a single date of service must be reported with one unit of HCPCS G0416, not the standard surgical pathology code.
In plain English: regardless of how many separate prostate biopsy cores or specimens are collected during one session, Medicare requires the entire set to be billed as a single unit under the G0416 code. Any and all submitted prostate needle biopsy specimens from a single patient must be reported with one unit of service of HCPCS code G0416. Since January 1, 2015, Medicare does not accept the standard surgical pathology code for prostate needle biopsy. It requires HCPCS code G0416, defined as surgical pathology, gross and microscopic examination, for prostate needle biopsy, any method, any number of specimens. If your Medicare bill for a prostate biopsy shows multiple pathology units, that is a billing error — and worth disputing.
Aetna began requiring G0416 for all prostate needle biopsies effective August 1, 2025, aligning with Medicare. If you are an Aetna member who had a prostate biopsy after that date and you see multiple pathology units on your bill, the same dispute logic applies. Always check your insurer's specific policy, since rules can vary by plan and date.
Common Pathology Billing Error Patterns: A Quick Reference
The table below summarizes the most common per-block vs. per-specimen billing error patterns and how to identify each on your itemized bill. Use this alongside your pathology report and your EOB.
| Error Type | What It Looks Like on Your Bill | The Correct Rule | How to Spot It |
|---|---|---|---|
| Block-level billing | Pathology line items far exceed number of specimens collected | One unit per separately submitted specimen (NCCI Ch. 10) | Compare unit count on bill to specimen count in pathology report |
| Prostate biopsy multi-unit billing (Medicare) | Multiple surgical pathology units billed for one prostate biopsy session | One unit of G0416 for all prostate needle biopsy specimens, same date of service | Look for more than one pathology charge on the same date as a prostate biopsy |
| Stain overbilling | Many immunohistochemistry (IHC) stain charges listed without medical necessity documentation | Only medically necessary stains are separately billable; add-on stain codes follow primary stain rules | Request lab report — each stain should be documented with clinical rationale |
| Duplicate specimen billing | Same specimen accessioned twice; two identical pathology charges on same date | Each specimen may only be billed once per date of service | Look for duplicate line items with the same date; cross-check accession log |
| Level upcoding | Higher-complexity pathology code billed for a routine biopsy without documentation of complexity | Specimen type — not block count — determines the complexity level billed | Compare code billed to specimen type listed in the pathology report |
How to Get the Documents You Need to Check Your Bill
You can't catch a per-block billing error without two key documents: your itemized bill and your pathology report. You have a legal right to both. The itemized bill lists every charge with the billing code and the number of units. The pathology report lists every specimen the lab received, usually labeled Specimen A, B, C, and so on, along with a gross description and microscopic findings for each.
Request both in writing from the hospital or lab. If the pathology was performed by an independent lab (common when your doctor sends tissue to an outside facility), you may need to contact the lab directly — the hospital bill may not include lab charges if they are billed separately. For a step-by-step explanation of how adjustments and charge lines work together, see our post on What 'Adjustments' on a Hospital Bill Really Mean in 2026.
Once you have both documents, count the number of distinct specimens in the pathology report and compare it to the number of pathology service units billed. For multiple units to be justified, the documentation must show separately identified specimens — for example, "Specimen A: Right upper lobe lung biopsy; Specimen B: Right lower lobe lung biopsy." Generic documentation like "multiple biopsies" without individual specimen identification does not support multiple units. If the units don't match, contact the billing department in writing and ask for a corrected itemized statement. If the dispute isn't resolved, you can escalate — for overcharges that hit your credit report, our article on Medical Debt & Credit Reports in 2026: What the CFPB Rule Change Means for You explains your rights.
What to Say When You Dispute
A written dispute letter to a hospital or lab billing department should be specific. Reference the date of service, the procedure that generated the tissue samples, the number of units billed, and the number of specimens documented in your pathology report. State that you are requesting a review under CMS NCCI Policy Manual Chapter 10, which governs units of service for surgical pathology. Ask for a written explanation of each unit billed and the corresponding accession number.
If the provider is billing Medicare and the overcharge affects your cost-sharing, you can also file a complaint with your Medicare Administrative Contractor (MAC) or request a redetermination under 42 CFR Part 405, Subpart I — the Medicare appeals process. CMS, acting through a Medicare Administrative Contractor or other contractor, will determine whether overpayments exist and will recoup any overpayments consistent with its policies and procedures. Providers have the right to appeal those determinations, and patients should familiarize themselves with the rules pertaining to when overpayments must be returned. If you believe the error constitutes a broader pattern rather than a one-time mistake, the HHS Office of Inspector General accepts complaints at oig.hhs.gov. If the billing dispute is moving toward collections, review your rights in our post on When Can a Hospital Send You to Collections? 2026 Rules.
About VerifyDoc: We help patients identify errors and overcharges on medical bills. We publish guides on hospital billing, the No Surprises Act, and disputing medical charges, updated as federal and state rules change.
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Check my bill — free preview →Frequently asked questions
My bill shows six pathology charges after a skin biopsy where the doctor removed three moles. Is that correct?
Not necessarily. If the doctor removed three distinct, separately labeled specimens, the correct billing should show three pathology units — one per specimen. Six units would only be appropriate if six separate specimens were submitted for separate examination and diagnosis. Request your itemized bill and the pathology report; the report should list each specimen with its own label (e.g., Specimen A, B, C). If the report shows three specimens but the bill shows six units, you have grounds to dispute the extra charges in writing to the billing department.
I had a prostate biopsy and my Medicare bill shows multiple pathology charges for the same date. What should I do?
This is a clear flag. Under CMS NCCI Policy Manual Chapter 10, effective January 1, 2026, all prostate needle biopsy specimens from a single Medicare patient on a single date of service must be reported as one unit of HCPCS code G0416 — not as multiple units of any other surgical pathology code. More than one unit of G0416 for the same date likely represents a billing error, though separately documented stains can be billed on their own. Write to the billing department, cite the NCCI Policy Manual Chapter 10, and ask for a corrected claim. If the issue isn't resolved, you can file a redetermination request with your Medicare Administrative Contractor under 42 CFR Part 405, Subpart I.
The pathology bill came from a separate company — not the hospital. Do the same rules apply?
Yes. The CMS NCCI per-specimen billing rule applies whether the service is billed by a hospital outpatient department on a UB-04 form or by an independent pathology lab or physician group on a CMS-1500 form. The unit-of-service rule does not change based on who sends the bill. What does change is who you contact to dispute: if the lab is independent, you'll write to the lab's billing department, not the hospital's. Make sure you obtain both the hospital's itemized bill and the lab's separate bill so you can compare all pathology charges against the single pathology report that covers your specimens.
Can a hospital or lab legally bill per block if it performed extra work processing each block?
No. The extra lab work involved in creating multiple tissue blocks from a single specimen — embedding, cutting, staining — is included in the base surgical pathology charge for that specimen. There is no separate billable code for block preparation under CMS rules. Some additional services like special stains or immunohistochemistry can be billed separately when medically necessary and documented, and those are counted per stain; a special stain can be counted again for another block only when that is medically necessary. The surgical pathology examination code itself is limited to one unit per separately submitted specimen, regardless of how much processing occurred in the lab.