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Explainer

What are 340B accumulators, and how does split billing work?

Short answer

A 340B accumulator is the running tally, kept by software, of how much of each drug (by 11-digit NDC) was given to each type of patient. Split billing is the process that uses those tallies to reorder: a hospital dispenses from one shared “neutral” inventory, and when the units given to 340B-eligible outpatients add up to a full package, the software places a replenishment order on the 340B account. Units given to inpatients go to the GPO account, and units given to ineligible outpatients go to a non-GPO WAC account. Every 340B order has to be backed by auditable records showing earlier use by eligible patients.[2][4][12]

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Three accounts

Where each dose is reordered

Hospitals subject to the GPO prohibition typically buy on three wholesaler accounts. Once drugs are back on the shelf they lose their identity as 340B, GPO or WAC stock. The accounts only decide how the next order is priced.[4][11]

340B account

Covered outpatient drugs given to 340B-eligible outpatients

Reordered at the 340B price only after eligible use has accumulated to a full package. Each order should trace back to specific eligible patients.[2][4]

GPO account

Drugs given to inpatients

Hospitals subject to the GPO prohibition (DSH hospitals, children’s hospitals and certain cancer hospitals) can’t obtain covered outpatient drugs through a GPO, but inpatient use isn’t covered outpatient use.[2][5][6]

WAC (non-GPO) account

Outpatients who don’t qualify for 340B, and the starting stock

Used for ineligible outpatient use and when a 340B price isn’t available. Hospitals have typically bought the first neutral stock at WAC before replenishment begins.[2][3][11]

Worked example

One NDC, one week, one accumulator

Illustrative numbers only. A hospital stocks an injectable sold in packs of 10 vials (one 11-digit NDC) and uses it in a mixed-use infusion area.

Event340B balanceGPO balanceWAC balanceOrder placed
Starting balance000—
Clinic visit, eligible outpatient: 4 vials400—
Admitted patient: 3 vials430—
Outpatient seen by a non-eligible prescriber: 2 vials432—
Eligible outpatient infusion: 7 vials1132—
Software checks balances1321 pack of 10 on the 340B account
  • The 340B side reached 11 vials, so one 10-vial pack is ordered at the 340B price and 1 vial carries forward. The GPO and WAC balances keep building until they reach a full pack.[4][12]
  • The order has to be traceable to the eligible encounters that built the balance. Under HRSA’s sample audit request, the 1 vial still waiting is already part of the 340B universe.[4][10]
Inside the software

Five checks before a unit counts as 340B

  1. 1

    Is the patient an inpatient or an outpatient?

    340B drugs can’t be used for hospital inpatients, so inpatient use always accumulates to the GPO side.[1][2]

  2. 2

    Does the outpatient meet the patient definition?

    The encounter has to happen at a registered, reimbursable location, with a provider the entity employs or contracts with, under HRSA’s 1996 patient definition guidelines.[1][2]

  3. 3

    Is Medicaid a payer on the claim?

    If the entity carves Medicaid out, any Medicaid claim (primary, secondary or tertiary) is excluded from 340B accumulation to avoid a duplicate discount.[5][12]

  4. 4

    Is it a covered outpatient drug?

    Products that fall outside the hospital’s written definition of covered outpatient drugs shouldn’t accumulate for 340B replenishment.[5][11]

  5. 5

    Does the NDC match exactly?

    Replenishment is tracked per 11-digit NDC, so the reordered product is the same product that was given to the patient.[12]

The same logic runs for contract pharmacies, where the TPA accumulates each pharmacy’s eligible claims by NDC and places 340B replenishment orders for that pharmacy. See how contract pharmacy setup works with a 340B TPA.[12]

Where accumulators go wrong

Moving accumulations between NDCs

Shortages and vial-size changes tempt staff to shift a balance from one NDC to another. Treat it as a compliance issue and document every exception.[12]

Charge-to-package conversion errors

If the charge code’s billing unit doesn’t convert correctly to package units, the tally drifts. Over-accumulating 340B is diversion even before an order is placed.[4]

Lost or missing charges

A dose that never reaches the data feed never accumulates, so the hospital rebuys it at WAC.[11]

Stale configuration

Out-of-date location, provider or drug mappings send units to the wrong account. Pharmacy Times lists infrequent split billing maintenance as a common cause of extra WAC spend.[11]

Records that don’t match inventory

The 2015 proposed guidance described a mismatch between recorded and actual 340B inventory as a form of diversion. Reconcile accumulator balances to purchases regularly.[4]

2026 update: the GPO policy for replenishment models

In 2013, HRSA said the GPO prohibition is violated as soon as a GPO is used to obtain covered outpatient drugs and “cannot be fixed or cured” by re-labeling the purchase afterward.[6][8]

On March 31, 2026, the U.S. District Court for the District of Columbia vacated that policy in Premier, Inc. v. HRSA, finding HRSA hadn’t given a reasoned explanation. HRSA’s policy release page now marks it as vacated, and HRSA did not appeal.[7][8][9]

What didn’t change: the statutory GPO prohibition, the bans on diversion and duplicate discounts, and HRSA’s 1994 guidance. The court said HRSA could reach the same conclusion with a better explanation, and it’s still unclear whether hospitals can now merge their GPO and WAC stock.[5][8]

How Aventi helps

Split billing and contract pharmacy on one platform

Independent TPA. Aventi runs split billing and contract pharmacy for 300 covered entities, 24 of them hospitals.

Traceable accumulations. Each balance ties back to the encounters and NDCs that built it, so you can answer an auditor’s sample from one place.

Ready for 2027. The rebate module is Included for Aventi TPA clients. Read how split billing, WAC purchasing and cash flow change under the rebate model.

Talk to us about split billing
FAQ

Accumulators and split billing: common questions

Software that tracks, drug by drug, how many units were given to 340B-eligible outpatients, inpatients and other outpatients. When the 340B balance for a drug reaches a full package, the drug can be reordered at the 340B price.[4]

It means splitting replenishment purchases across accounts (340B, GPO and WAC) based on who actually received the drug, so a hospital can run one physical inventory in mixed-use areas like the emergency department, infusion center or cath lab.[1][2][11]

No. A hospital can keep separate physical 340B inventories instead. But in mixed-use settings HRSA requires a tracking system that keeps 340B drugs away from inpatients, and if a hospital can’t track it effectively, it shouldn’t use 340B in that setting.[1]

The 11-digit NDC identifies the manufacturer, product and package size. Hospitals accumulate and replenish on an exact 11-digit match so the 340B purchase is the same product used for the eligible patient. Document any case where an exact match isn’t possible.[12]

In March 2026 a federal court vacated HRSA’s 2013 GPO policy, which said a hospital couldn’t fix a GPO purchase of covered outpatient drugs by re-labeling it afterward. HRSA didn’t appeal. The statutory GPO prohibition still applies, and the court said HRSA could reach the same conclusion again with a reasoned explanation, so keep your accumulator records audit-ready.[5][7][8][9]

HRSA’s sample audit data request asks whether you use physical or virtual inventory and, for virtual inventory, treats all accumulations designated as 340B as part of the 340B universe, whether or not they’ve been replenished yet. Auditors sample individual administrations and may ask someone to walk them through the split billing software.[10]

HRSA’s FAQ says to work with the manufacturer first, then buy at WAC. A GPO purchase is a last resort that requires notifying HRSA, keeping records and trying the 340B price on every order.[3]

For drugs in the rebate pilot, hospitals buy at WAC and claim a rebate later, so purchasing accounts and cash flow change. Aventi’s rebate module is Included for Aventi TPA clients.340B rebate model · Split billing and cash flow under the rebate model

Related pages

Sources

  1. HRSA FAQ, May a hospital use 340B-priced drugs in “mixed-use” settings, such as a surgery department, where both inpatients and outpatients are treated? — https://www.hrsa.gov/about/faqs/may-hospital-use-340b-priced-drugs-mixed-use-settings-such-surgery-department-where-both-inpatients
  2. HRSA FAQ, Our mixed-use area has only inpatients or 340B eligible outpatients … is it required to start with a WAC inventory? — https://www.hrsa.gov/about/faqs/our-mixed-use-area-has-only-inpatients-or-340b-eligible-outpatients-we-do-not-have-any-340b
  3. HRSA FAQ, When a covered entity is unable to purchase a covered outpatient drug at a 340B price, may the covered entity subject to the GPO prohibition buy via a GPO? — https://www.hrsa.gov/about/faqs/when-covered-entity-unable-purchase-covered-outpatient-drug-340b-price-may-covered-entity-subject
  4. Federal Register, 340B Drug Pricing Program Omnibus Guidance (proposed), 80 FR 52300 (Aug. 28, 2015) — https://www.federalregister.gov/documents/2015/08/28/2015-21246/340b-drug-pricing-program-omnibus-guidance
  5. 42 U.S.C. § 256b, Limitation on prices of drugs purchased by covered entities (Cornell LII) — https://www.law.cornell.edu/uscode/text/42/256b
  6. HRSA, 340B Program Notice Release No. 2013-1, Statutory Prohibition on Group Purchasing Organization Participation (Feb. 7, 2013) — https://www.hrsa.gov/sites/default/files/hrsa/opa/prohibition-gpo-participation-02-07-13.pdf
  7. HRSA, 340B Policy Releases (notes Release 2013-1 vacated by Premier, Inc. v. HRSA, No. 24-cv-3116, D.D.C. Mar. 31, 2026) — https://www.hrsa.gov/opa/program-requirements/policy-releases
  8. ArentFox Schiff, Federal Court Vacates HRSA’s 2013 340B ‘GPO Prohibition’ Policy for Replenishment Models (Apr. 14, 2026) — https://www.afslaw.com/perspectives/alerts/federal-court-vacates-hrsas-2013-340b-gpo-prohibition-policy-replenishment
  9. Premier Inc. newsroom, Premier, Hospitals Laud HRSA’s Move to Not Appeal Ruling that Struck Down Drug Purchasing Restrictions Policy (June 12, 2026) — https://premierinc.com/newsroom/news/premier-hospitals-laud-hrsas-move-to-not-appeal-ruling-that-struck-down-drug-purchasing-restrictions-policy
  10. 340B Prime Vendor Program (Apexus), Sample HRSA 340B Audit Data Request List for Covered Entities — https://www.340bpvp.com/Documents/Public/340B%20Tools/sample-hrsa-340b-audit-data-request-for-covered-entities.pdf
  11. Pharmacy Times, Minimizing WAC Exposure to Decrease Drug Expense in the Virtual Inventory Setting — https://www.pharmacytimes.com/view/minimizing-wac-exposure-to-decrease-drug-expense-in-the-virtual-inventory-setting
  12. University of Toledo Medical Center, Policy 3364-133-119: 340B Program (effective Mar. 21, 2025) — https://www.utoledo.edu/policies/utmc/pharmacy_hsc/pdfs/3364-133-119.pdf

Last updated November 11, 2026. This page is general information, not legal advice. The 2015 omnibus guidance was proposed and is cited only for how HRSA described replenishment models.