Can I resubmit an AC4 claim with the same referring number?

Only if the original rejection was a format problem you have now fixed, such as restoring a leading zero. If the number is an NP or midwife number on a code that does not accept that range, resubmitting the same pair will produce AC4 again.

Is AC4 the same as a missing referring number?

No. A missing referring physician number is a different error (ARF or ARP on the Ministry list). AC4 means a number was present and was not accepted for this service code.

Why does AC4 keep firing on nurse practitioner referrals?

The Ministry rejects an NP number in the range 722900-744292 when the fee schedule code is not eligible for an NP referral. The Claims Error Report conditions list G310, G313, and G700 among acceptable cardiology examples, plus enumerated laboratory codes. If your EMR stores an NP as the default referrer for every consult, AC4 is the designed outcome on every ineligible code.

Is an AC4 claim recoverable after the three-month window?

If the original claim reached the Claims Error Report inside three months of the service date, INFOBulletin 230402 allows a corrected resubmission through the Ministry stale-date process even after the three-month window. If the claim was never submitted in time, payment may be recoverable by written application where documentation supports it, which is a separate process from a corrected resubmit.

OHIP error report

AC4

Provider registration and referrals

OHIP error code AC4: unaccepted referring provider number

AC4 means the referring or requisitioning provider number on the claim is unaccepted for this fee schedule code. The Ministry rejects numbers that are not six digits, that match your own billing number, or that fall in the NP or midwife ranges on an ineligible code.

Ministry wording: Unaccepted referral number. Most often affects Internal medicine, Psychiatry, Neurology, Hospitalists, Orthopaedic surgery.

You already know AC4. A single rejection is rarely the whole pile. Specialists we work with recover $10,000 to $100,000+ from rejected and unpaid claims.

1Why it fires
2What it costs
3Whether it is recoverable

See if this is recoverable

AC4 at a glance

AC4 is an A-series Claims Error Report code. The claim is rejected at validation and does not reach the Remittance Advice as a paid or adjusted item. The Ministry of Health publishes four concrete rejection reasons under this code: the referring number is not six numerics, the referring number equals the practitioner billing number, the referring number falls in the nurse practitioner range 722900-744292 on a fee schedule code that is not eligible for an NP referral, or the referring number falls in the midwife range 700000-722899 on a fee schedule code that is not eligible for a midwife referral.

That is different from a missing referring number. ARF and ARP on the Ministry list cover missing or required referring-physician fields. AC4 means a number was present and failed one of the acceptance tests above. It is also different from EQ6 (the number is not registered) and ERF (the number is registered but currently ineligible to refer).

For specialists, AC4 usually surfaces on consultations, e-consults, and diagnostic services that have a technical and professional component, because those listings require a referring or requisitioning health care provider number. The Schedule of Benefits defines a consultation as an assessment rendered following a written request from a physician, a nurse practitioner, or a dental surgeon in connection with an insured dental procedure in hospital. That definition does not override the AC4 range rules. An NP or midwife number is accepted only when the fee schedule code itself is eligible for that referrer type.

Why it fires

The referring number is not exactly six digits.
The referring number is the same as your own billing number on a code that does not allow self-referral.
The number falls in the nurse practitioner range (722900-744292) and the fee schedule code is not eligible for an NP referral.
The number falls in the midwife range (700000-722899) and the fee schedule code is not eligible for a midwife referral.

The first Ministry reason is format. Six numerics, nothing else. A five-digit store in the EMR, a dropped leading zero, a CPSO number pasted into the billing-number field, or a group clinic identifier will fail this edit. V09 also polices invalid referral-number formats and ranges. Which code fires first depends on the claim shape, but the clinic fix is the same: put the six-digit OHIP billing number in the referring field.

The second Ministry reason is self-referral. If the referring number equals the practitioner billing number, AC4 fires unless the Schedule listing allows that pattern. A common clinic workaround when a patient arrives without a letter is to type the billing physician’s own number so the software will submit. That value is exactly what AC4 rejects.

The third and fourth reasons are referrer-type limits. The Ministry names the NP range 722900-744292 and the midwife range 700000-722899. The detailed Claims Error Report conditions for AC4 enumerate examples clinics hit constantly: C813 and C815 require a midwife-range number, and for cardiology services the acceptable NP referral codes listed are G310, G313, and G700. Other cardiology listings with an NP number in the referring field reject. Laboratory L-codes have their own NP-eligible tables under the same conditions. Do not assume every consultation listing accepts every NP number just because the Schedule allows an NP to request a consultation in principle.

Clinic patterns that produce repeat AC4 are almost always master-data problems. The address book stores five digits. It stores a CPSO number. It stores a midwife or NP as the default referrer for every consult. Or booking staff invent a number when the letter is blank. Correcting one claim without fixing the row leaves the next claim on the same path.

What it costs

The claim is rejected outright. Nothing is paid until a corrected claim is accepted. The amount at risk is the full fee for that consultation or diagnostic service, which varies by fee schedule code.

Unlike some Remittance Advice adjustments, AC4 does not pay a reduced visit in the same cycle. The item is off the payment run. If the practice does not correct and resubmit, the entire professional fee for that encounter is unpaid.

Consultation listings are the high-value cases. A single missed consult for internal medicine, psychiatry, or neurology is a full consult fee, not a clerical nuisance. Diagnostic requisitions that need a requisitioning number, including electrocardiography professional components billed under codes such as G310 and G313, add a second loss stream when the same bad referrer row is reused.

The submission window for services rendered on or after 1 April 2023 is three months from the date of service, per Ministry INFOBulletin 230402. An AC4 that sits on the error report without correction can age into a stale-dated problem even though the original rejection was a referrer-number edit, not a clinical denial.

Fee codes this most often affects

C813 · Midwife or Aboriginal Midwife-Requested Assessment: The Claims Error Report conditions for AC4 name this listing with C815. It rejects when the referral number sits outside the midwife range 700000-722899.
C815 · Midwife or Aboriginal Midwife-Requested Special Assessment: Carries the same midwife-range requirement as C813. A family physician number on this listing is an AC4 by design, not an oversight.
G310 · Electrocardiography: One of three cardiology services the Claims Error Report conditions list as acceptable on a nurse practitioner referral.
G313 · Electrocardiography: Accepted on a nurse practitioner referral under the same Claims Error Report conditions. Other cardiology listings with an NP number in the referring field reject.
G700 · Basic fee-per-visit premium for procedures marked (+): The third cardiology listing enumerated as acceptable for nurse practitioner referrals under those conditions.

Listings and descriptions are from the OHIP Schedule of Benefits. Amounts change with each fee schedule update, so confirm the current value before you rely on it.

Step-by-step: how to clear this rejection

Read the Claims Error Report line and confirm the code is AC4, not EQ6, ERF, ARF, ARP, or V09.
Pull the original consultation request or requisition and identify the six-digit OHIP billing number of the person who requested the service.
Check whether that number equals your own billing number, falls in the NP range 722900-744292, or falls in the midwife range 700000-722899.
If the number is NP or midwife, confirm the fee schedule code is one the Ministry accepts for that referrer type before you resubmit the same pair.
Correct the referring field, or change the fee schedule code when the referrer type is the constraint, and resubmit inside the three-month window.

Work the report in order. AC4 is an acceptance edit, not a registration edit. Confirming that the number “looks familiar” is not enough. Match it to the written request, then match the request to the fee schedule code you billed.

If the only available referrer is an NP or midwife and the code you billed does not accept that range, resubmitting the same pair will produce AC4 again. You need either an eligible code for that referrer type or a physician referrer who actually requested the service. Do not invent a substitute number.

Log the original rejection date, the corrected number or code, and the resubmission date. A second AC4 on the same address-book row means the master record is still wrong.

Money you already earned, still unpaid

Recovery is separate work from ongoing billing. Charging only a percentage of what we recover, we review the backlog, correct what your documentation supports, and resubmit. Recent engagements have recovered five- and six-figure amounts, including rejected claims well past the 3-month stale dated deadline going back into 2023.

The alternative is usually your evenings or admin blocks, not billable clinic time. No setup or service fees. Every dollar recovered is money already written off, you keep most of it, and you pay nothing if nothing comes back.

“These claims weren’t chased up on. These claims have been stale dated. You add up the volume of money in there and it’s a consequential sum.”

Dr Sanjay Acharya, on what the recovery review found

Show me what is still recoverable

How to fix it going forward

Store referring providers in the EMR by six-digit OHIP billing number, not CPSO number or truncated digits.
Block self-referral on consultation and requisition codes unless the Schedule listing explicitly allows it.
When the referrer is an NP or midwife, confirm the fee schedule code is eligible for that referrer type before you submit.
Train booking staff to capture the referrer number from the consultation request, not from memory or a stale address-book row.

The durable fix is data quality in the referrer file. Review address-book records that fail AC4 twice. Those rows are usually wrong in the same way every time: five digits, a group number, a CPSO number, or a student identifier.

For NP and midwife referrals, keep a short internal list of the consultation, laboratory, and diagnostic codes your group actually uses that accept those ranges. The Ministry condition is code-specific. Using any other code with an NP or midwife number is a designed AC4.

Separate intake from billing. The person who books the consult should record the referrer from the signed request. The person who submits the claim should not be inventing a value to satisfy a required field.

Is it recoverable?

Recoverable by resubmission inside the window

Correct the referring number, or the fee schedule code when the referrer type is the constraint, and resubmit inside the three-month window from the date of service.

If the original claim reached the Claims Error Report inside three months of the service date, a corrected resubmission remains the first path. Replace the number with the six-digit billing number from the written consultation request. If the only available referrer is an NP or midwife and the code you billed does not accept that range, change the code or obtain an eligible physician referrer. Do not keep resubmitting the same pair.

INFOBulletin 230402 also allows claims that reached the Claims Error Report inside three months to be corrected and resubmitted through the Ministry stale-date process after the three-month window. If the claim was never submitted in time, payment may be recoverable by written application where documentation supports it. That is a separate process from a routine resubmit, and this page does not cover how that application is prepared.

For in-province services on or after 1 April 2023, claims must be submitted within three months of the date of service, not six. Ontario INFOBulletin 230402 is the Ministry notice. Many third-party pages still quote six months. That window is closed for current work. If the original claim reached the Claims Error Report inside three months, a corrected resubmission can still be filed after the window in the Ministry's stale-date process. If the claim was never submitted in time, payment may be recoverable by written application. That is not a routine resubmit.

Related codes

Frequently asked questions

What does OHIP error code AC4 mean?: AC4 means the referring or requisitioning provider number on the claim is unaccepted. The Ministry rejects numbers that are not six digits, that match your own billing number, or that belong to a nurse practitioner or midwife on a fee schedule code that does not allow that referrer type.
Can I resubmit an AC4 claim with the same referring number?: Only if the original rejection was a format problem you have now fixed, such as restoring a leading zero. If the number is an NP or midwife number on a code that does not accept that range, resubmitting the same pair will produce AC4 again.
Is AC4 the same as a missing referring number?: No. A missing referring physician number is a different error (ARF or ARP on the Ministry list). AC4 means a number was present and was not accepted for this service code.
Why does AC4 keep firing on nurse practitioner referrals?: The Ministry rejects an NP number in the range 722900-744292 when the fee schedule code is not eligible for an NP referral. The Claims Error Report conditions list G310, G313, and G700 among acceptable cardiology examples, plus enumerated laboratory codes. If your EMR stores an NP as the default referrer for every consult, AC4 is the designed outcome on every ineligible code.
Is an AC4 claim recoverable after the three-month window?: If the original claim reached the Claims Error Report inside three months of the service date, INFOBulletin 230402 allows a corrected resubmission through the Ministry stale-date process even after the three-month window. If the claim was never submitted in time, payment may be recoverable by written application where documentation supports it, which is a separate process from a corrected resubmit.

References

For how error reports relate to the remittance advice, see how to read your OHIP remittance advice and what rejection codes actually mean. Official wording for this code: Ministry of Health, Error Report Rejection Conditions (December 2022).