Modifiers · HCPCS modifier

Medical-policy requirements met

Modifier KX is a two-character HCPCS Level II modifier appended to a claim line to certify that every coverage requirement spelled out in the applicable medical policy has been satisfied and that supporting documentation is on file. It functions as the billing provider's or supplier's formal attestation—not merely a flag—that the service or item is medically necessary and policy-compliant.

Verified May 8, 2026 · 11 sources ↓

Type: HCPCS
CPT codes use it: 22
Top regions: General, Spine, Foot & ankle

Drawn from Palmetto GBANoridianCMSFCSOPremera

When to use modifier KX

Source · Editorial brief grounded in 11 cited references ↓

Append modifier KX when a payer's Local Coverage Determination (LCD) or medical policy explicitly requires it as a condition of payment. In outpatient physical therapy (PT), occupational therapy (OT), and speech-language pathology (SLP), CMS mandates modifier KX on every claim line once cumulative annual charges cross the therapy threshold (formerly called the therapy cap). Its presence certifies that the clinician has determined continued treatment is medically necessary and that the patient's medical record contains documentation justifying services beyond that threshold. Without it, the claim will automatically deny at the threshold amount.

For durable medical equipment, prosthetics, orthotics, and supplies (DMEPOS), modifier KX signals that the supplier has verified all LCD coverage criteria are met—qualifying diagnosis, face-to-face evaluation, written order, and any other policy-specific prerequisites—and that documentation is available upon request. A concrete example is therapeutic shoes for persons with diabetes (TSPD): the supplier appends KX only after confirming the patient has a diabetes diagnosis plus at least one qualifying foot condition, the certifying physician has provided written medical-necessity documentation, and a face-to-face visit occurred within six months before delivery.

Two additional, often-overlooked use cases exist. First, modifier KX resolves gender/procedure conflicts in the NCCI Procedure-to-Procedure (PTP) edit tables; when a sex-specific service is billed for a patient with ambiguous genitalia or a transgender patient, KX tells the MAC the conflict is not a keying error so the claim can continue processing. Second, effective January 1, 2023, dentists and physicians may append KX to dental claims to attest that the dental service is inextricably linked to a covered medical procedure—for example, pre-operative oral infection clearance before cardiac valve surgery—and that coordination of care between the dental and medical providers has occurred and is documented.

Orthopedic scenarios

Concrete situations in orthopedic practice that warrant modifier KX.

Source · Editorial brief grounded in AAOS coding guidance and cited references ↓

Total knee arthroplasty (TKA) rehabilitation: A patient's combined PT charges surpass the annual Medicare therapy threshold mid-course. The physical therapist documents functional progress, persistent gait deficits, and medical necessity for continued skilled care in the plan of care. Modifier KX is appended to each subsequent PT procedure code (e.g., 97110, 97116, 97530) so the claim processes above the threshold rather than auto-denying.
Post-ORIF tibial plateau fracture OT: After open reduction internal fixation, the patient begins outpatient OT for upper-extremity weight-bearing restrictions affecting ADLs. Once cumulative OT charges cross the threshold, the occupational therapist attests medical necessity in the record and appends KX to codes such as 97530 and 97535 on each claim line to avoid threshold-based denial.
Knee arthroscopy with meniscectomy—therapeutic shoe tangent: A diabetic patient with peripheral neuropathy and a prior plantar ulcer undergoes arthroscopic partial medial meniscectomy. Separately, the DME supplier billing for post-operative therapeutic footwear appends modifier KX to the HCPCS shoe/insert codes only after confirming the certifying physician's diabetes management documentation, the neuropathy and ulcer history, and a face-to-face visit within six months—not simply because the patient had a recent orthopedic procedure.
Lumbar spinal fusion pre-operative dental clearance: A patient scheduled for posterior lumbar interbody fusion (PLIF) requires extraction of an abscessed tooth that poses surgical infection risk. The dentist bills the extraction with modifier KX, attesting that the dental service is inextricably linked to the covered spinal procedure, that peer-reviewed literature supports clearance before implant placement, and that documented coordination with the spine surgeon is in the medical record.

Common mistakes

Where coders most often go wrong with modifier KX.

Source · Editorial brief grounded in CMS NCCI Policy Manual and cited references ↓

Appending KX without confirming the specific LCD or medical policy requirement is satisfied—using it as a generic 'please pay this' flag rather than a documented attestation voids its protective function and exposes the claim to RAC recovery.
Omitting KX on every claim line once the therapy threshold is crossed, not just the line that first exceeds it—each individual PT, OT, or SLP procedure code line above the threshold must carry the modifier independently.
Applying KX to DMEPOS claims before a face-to-face evaluation has occurred or before the physician's written order is in hand—policy criteria must be fully satisfied before attestation, not after the equipment ships.
Failing to retain contemporaneous documentation that supports the KX attestation; CMS Recovery Audit Contractors (RACs) specifically target therapy claims billed with KX for post-payment review, and missing records convert a paid claim into an overpayment.
Pairing KX with the GY modifier only when the intent is to seek a denial for secondary-payer purposes on dental claims—KX alone processes for Medicare payment, while the KX + GY combination signals a statutorily excluded service needing a denial notice.
Confusing modifier KX with modifier KF (item designated by FDA as Class III) or modifier KZ (new coverage not implemented by managed care plan)—each two-character K-series modifier has a distinct, non-interchangeable function.

CPT codes that use modifier KX

22 orthopedic CPT codes in our reference list this modifier as applicable. Sorted by total RVU.

Source · Derived from per-code modifier guidance in our CPT reference

Showing top 12 of 22 by total RVU.

Where modifier KX shows up

Body regions where this modifier most commonly appears in our orthopedic reference.

General 13 codes
Spine 4 codes
Foot & ankle 2 codes
Hip 1 code

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 11 cited references ↓

01Is modifier KX required on every therapy claim, or only after the threshold is crossed?

KX is required only on claim lines where the patient's cumulative PT/SLP or OT charges have reached or exceeded the annual Medicare therapy threshold. Claims below the threshold do not need it, and adding it unnecessarily may trigger unnecessary scrutiny without providing any billing benefit.

02Does appending modifier KX guarantee Medicare will pay the claim?

No. KX makes the claim eligible to process above the therapy threshold or to bypass certain coverage edits, but it does not override a finding of medical non-necessity on post-payment review. CMS Recovery Audit Contractors specifically audit KX-flagged therapy claims; if documentation does not support medical necessity, the payment will be recouped.

03Can modifier KX be used on orthopedic surgery claims for TKA or arthroscopy?

Not directly on the surgical code itself under typical circumstances. Its primary orthopedic relevance is in post-surgical outpatient rehabilitation claims that cross the therapy threshold, and in DMEPOS claims (e.g., diabetic footwear, orthoses) where an LCD mandates it as a coverage attestation.

04What documentation must be on file when modifier KX is appended to a DMEPOS claim?

At minimum: a detailed written order from the treating practitioner, documentation of a face-to-face clinical evaluation, a diagnosis that satisfies the LCD coverage criteria, and clinical notes that demonstrate medical necessity. The documentation must exist before the item is delivered—not reconstructed after a post-payment audit request.

05How does modifier KX interact with modifier GY on dental claims?

When a dental service is inextricably linked to a covered medical procedure, bill KX alone to seek Medicare payment. If the dental item is statutorily excluded and a formal denial is needed for a secondary payer, bill both KX and GY on the same claim line; KX signals the inextricable-linkage attestation while GY triggers the denial notice required by the secondary insurer.

06Which MACs and payers recognize modifier KX beyond Medicare?

All Medicare Administrative Contractors (MACs) recognize modifier KX under CMS policy. Several commercial payers—including some Blue Cross Blue Shield affiliates—have adopted it in their own payment policies to signify that plan-specific medical policy criteria have been met, though payer-specific rules vary and should be confirmed individually.

07What is the RAC audit risk associated with modifier KX on therapy claims?

CMS RAC topic 0A339 specifically targets PT, OT, and SLP claims billed with modifier KX for review of medical necessity and documentation compliance. High-volume KX billing relative to peer norms increases audit probability; robust, contemporaneous functional documentation is the primary defense.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

MODIFIER KX — AI SCRIBE GUIDANCE Modifier KX must appear on the claim line when Medicare or another payer's medical policy requires documented attestation that all coverage criteria are met. For outpatient PT, OT, or SLP services, the treating clinician must ensure the medical record contains: (1) a current, signed plan of care; (2) objective functional measures demonstrating medical necessity for continued skilled services; and (3) explicit documentation that the patient's cumulative therapy charges have crossed the applicable annual threshold and that further treatment remains reasonable and necessary. Each procedure code line above the threshold needs its own KX modifier—it cannot be applied once to a claim and inherited by remaining lines. For DMEPOS, confirm that the qualifying diagnosis, physician's written order, and face-to-face visit are all documented before appending KX. Do not autopopulate KX on every claim; generate it only when policy-specific prerequisites are verifiably satisfied and charted.

See how Mira flags modifier KX in dictation