Modifiers · HCPCS modifier

Left side

Modifier LT is a HCPCS Level II anatomic modifier appended to a procedure or supply code to tell the payer that the service was performed on the left side of the body. It eliminates ambiguity on claims involving paired structures—think left knee, left shoulder, left hip—and helps payers distinguish a unilateral left-side service from a right-side or bilateral service billed on the same or a subsequent date.

Verified May 8, 2026 · 7 sources ↓

Type: HCPCS
CPT codes use it: 1,529
Top regions: Foot & ankle, Hand, Wrist

Drawn from CMSCGSEmblemHealth: CorrectCMAAMA

When to use modifier LT

Source · Editorial brief grounded in 7 cited references ↓

Append modifier LT whenever you perform a unilateral procedure on a left-sided structure and the CPT or HCPCS code does not already specify laterality in its descriptor. Classic orthopedic examples include a left total knee arthroplasty (CPT 27447), left knee arthroscopy with meniscectomy (CPT 29881), or left distal radius ORIF (CPT 25600-series). The modifier signals to the payer that only the left side was treated, which is critical when the same code could plausibly apply to either limb.

For bilateral same-session procedures, do not stack LT and RT on one claim line. Instead, bill two separate claim lines—one with LT and one with RT, each carrying one unit of service—unless payer policy requires modifier 50 for a bilateral procedure designation. Medicare and most DME MACs specifically reject a combined RTLT modifier on a single claim line. When the procedure code carries a bilateral surgery indicator of '1' in the Medicare Physician Fee Schedule and both sides are done at the same operative session, modifier 50 is generally the correct choice rather than LT/RT; confirm the bilateral surgery indicator before choosing between these approaches.

Modifier LT is also an NCCI PTP-associated anatomic modifier, meaning it can be used—when clinically justified—to bypass a National Correct Coding Initiative Procedure-to-Procedure edit. For example, if two procedures are performed on separate anatomic sites (left knee and left hip on the same date), LT on one code and a separate anatomic modifier on the other can document that the services occurred at distinct locations. Never append LT solely to circumvent an edit when the clinical facts do not support separate anatomic sites.

Orthopedic scenarios

Concrete situations in orthopedic practice that warrant modifier LT.

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

Left total knee arthroplasty: Report CPT 27447-LT to distinguish the left-side procedure from a prior right TKA (27447-RT) already in the patient's claims history.
Left knee arthroscopy with partial medial meniscectomy: Append LT to CPT 29881 when only the left knee is scoped so the claim does not trigger a duplicate-service edit against a right-side procedure billed the same day.
Left distal radius ORIF with plate fixation: Use CPT 25609-LT to document the left wrist operative site; pair with ICD-10-CM S52.501A (left distal radius fracture) for laterality consistency.
Left hip total arthroplasty: Append LT to CPT 27130 when only the left hip is replaced; if the right hip is replaced at a separate session within the same admission, bill 27130-RT on a distinct claim line.
Left shoulder rotator cuff open repair: Report CPT 23412-LT for a left-sided full-thickness supraspinatus repair; omitting LT risks a duplicate denial if CPT 23412-RT was filed within the global surgery window.
Bilateral knee injections billed separately: If a corticosteroid injection (CPT 20610) is given to both knees in the same encounter, bill 20610-LT and 20610-RT on two claim lines—not a single line with two units—per CMS bilateral billing rules.

Common mistakes

Where coders most often go wrong with modifier LT.

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

Billing a combined RTLT modifier on a single claim line instead of two separate claim lines with LT and RT respectively—this triggers rejection under Medicare DME MAC policy.
Appending modifier LT to a CPT code whose descriptor already states 'bilateral,' such as certain bilateral arthroscopy or bilateral turbinate ablation codes, which makes the modifier redundant and can cause a claim denial.
Using modifier LT instead of modifier 50 for same-session bilateral total knee arthroplasty (27447 billed twice); when the MPFS bilateral surgery indicator is '1,' modifier 50 is the appropriate designator, not separate LT and RT lines.
Omitting modifier LT entirely on a left-side-only procedure like a left shoulder rotator cuff repair (CPT 23412) when the same code was billed for the right side within the global period, causing the second claim to reject as a duplicate.
Appending modifier LT to a unilateral CPT code without also updating the diagnosis pointer to a left-lateralized ICD-10-CM code (e.g., using M17.11 left primary osteoarthritis for a left TKA), creating a laterality mismatch that flags during payer review.
Using modifier LT to bypass an NCCI PTP edit when the two procedures were actually performed in contiguous structures of the same anatomic region—LT does not justify separate billing in that scenario.

CPT codes that use modifier LT

1,529 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 1,529 by total RVU.

Where modifier LT shows up

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

Foot & ankle 335 codes
Hand 207 codes
Wrist 165 codes
Knee 164 codes

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01Can modifier LT be used on every CPT code?

No. Modifier LT is appropriate only for procedures performed on anatomic structures that have a left-side counterpart. It should not be appended to codes whose descriptors already specify bilateral performance or to procedures performed on midline structures with no left-right distinction. Always verify the MPFS bilateral surgery indicator before applying LT.

02What is the difference between modifier LT and modifier 50 for bilateral orthopedic procedures?

Modifier 50 signals that a single procedure was performed bilaterally in the same operative session and triggers a 150% payment adjustment for Medicare. Modifiers LT and RT are used when two distinct unilateral procedures are billed separately—either at different sessions or on separate claim lines for the same date—to identify which side each line represents. When the MPFS bilateral surgery indicator equals '1,' use modifier 50 for same-session bilateral work rather than separate LT and RT lines.

03Does modifier LT affect reimbursement?

Modifier LT is an informational anatomic modifier and does not itself change the payment rate; it clarifies laterality to prevent duplicate-claim denials and support medical necessity review. Payment adjustments are driven by modifier 50 for bilateral procedures, not by LT alone.

04Can modifier LT bypass an NCCI PTP edit?

Yes, but only when the clinical circumstances genuinely support it. The CMS NCCI Policy Manual classifies LT as an NCCI PTP-associated anatomic modifier, meaning it can be used to override an edit when two procedures are performed at distinctly separate anatomic sites on the same date. It cannot be used solely to circumvent an edit when the procedures were performed in contiguous structures of the same anatomic region.

05What documentation is required to support modifier LT?

The operative report, procedure note, or clinical documentation must explicitly state that the procedure was performed on the left side. A laterality-specific ICD-10-CM diagnosis code (e.g., M17.11 for left primary knee osteoarthritis) should accompany the claim to corroborate the modifier. Mismatch between the diagnosis laterality and the LT modifier is a common audit flag.

06How should a DME supplier bill for bilateral items using modifier LT?

Medicare DME MAC policy requires two separate claim lines: one line with the HCPCS supply code and modifier LT, and a second line with the same code and modifier RT, each with one unit of service. Billing both modifiers on a single claim line—or billing two units without laterality modifiers—will result in claim rejection per CGS Medicare bilateral modifier policy.

Sources & references

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

01CMS 2025 Medicare NCCI Policy Manual, Chapter 1 – https://www.cms.gov/files/document/01-chapter1-ncci-medicare-policy-manual-2025finalcleanpdf.pdf
02CMS Billing and Coding: Use of Laterality Modifiers (Article A56869) – https://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=56869
03CGS Medicare RT and LT Modifiers Fact Sheet – https://www.cgsmedicare.com/jc/education/fact_sheets/bilateral_modifiers.html
04CMS Medicare NCCI FAQ Library – https://www.cms.gov/medicare/coding-billing/national-correct-coding-initiative-ncci-edits/medicare-ncci-faq-library
05EmblemHealth: Correct Usage of Modifier 50 and Modifiers LT and RT for Bilateral Procedures (03/31/2025) – https://www.emblemhealth.com/providers/claims-corner/coding/correct-usage-of-modifier-50-and-modifiers-lt-and-rt-for-bilater
06CMA: Coding Corner – How to Appropriately Apply Modifiers LT, RT, and 50 (March 2019) – https://www.cmadocs.org/newsroom/news/view/ArticleId/27965/Coding-Corner-How-to-appropriately-apply-modifiers-LT-RT-and-50
07AMA CPT Professional Edition – Appendix A, Modifier Descriptions (current year)

Mira AI Scribe

When AI scribe or ambient documentation tools capture a procedure performed on the left side of the body, the downstream coding workflow should automatically flag modifier LT for attachment to the relevant CPT or HCPCS code. For orthopedic encounters, the scribe should record explicit laterality language—'left knee,' 'left shoulder,' 'left hip'—in the operative or procedure note so that the coder has unambiguous documentation support for modifier LT. Without that laterality documentation, a payer audit can result in recoupment even if the modifier was applied correctly at the time of billing. AI tools should also cross-check whether the selected CPT code already describes a bilateral procedure, in which case LT may be inappropriate or redundant. Structured laterality capture at the point of documentation is the single most effective way to ensure modifier LT is applied accurately and defensibly.

See how Mira flags modifier LT in dictation