Medical coding requires precision to document and bill for services provided to a patient. Modifiers LT (Left Side) and RT (Right Side) are two-character codes appended to procedure codes (CPT or HCPCS Level II) to indicate laterality. Their purpose is to specify which side of the body a procedure or service was performed on. These modifiers communicate to the payer whether the service was delivered to a paired organ, like a kidney, or an extremity, such as an arm or leg. Correct application of LT and RT ensures the medical record is clear and helps prevent claim denials that arise from ambiguous or incomplete location information.
Foundational Rules for Unilateral Coding
The primary function of the LT and RT modifiers is to specify the anatomical location when a procedure is performed on a paired body structure. These are used when the procedure code itself does not contain any reference to laterality. When a service is performed unilaterally, the appropriate laterality modifier must be attached to the procedure code on the claim form. This informs the payer that the procedure was performed on the left or the right side.
Failing to use the correct laterality modifier in a unilateral scenario can lead to claim rejection. Without LT or RT, the payer cannot assume the location of the service, often resulting in a denial or a request for additional documentation. For example, an injection into a single knee joint requires the appropriate modifier, RT or LT, to clarify which knee received the treatment. These two-character codes are designated as HCPCS Level II modifiers, and their use is mandated by many payers, including Medicare, for certain codes to ensure correct reimbursement.
Proper Application for Bilateral Services
Procedures performed on both sides of the body during the same operative session are considered bilateral. The most common method for reporting a bilateral procedure is by using Modifier 50 (Bilateral Procedure) on a single line item. Modifier 50 is the standard practice, especially for Medicare claims, and it typically results in a payment adjustment based on the fee schedule amount for a single procedure.
Confusion arises because not all payers accept Modifier 50, and some procedures are not eligible for it. An alternative method required by some commercial payers is to report the procedure on two separate lines, with one line using Modifier LT and the other using Modifier RT. In this scenario, the procedure code is listed twice, each with a quantity of one unit of service. A third, less common method is to use the LT and RT modifiers and report a quantity of two units for the procedure code.
The correct billing method is dependent on the payer’s guidelines, making it necessary to verify their policy before submitting a claim. Using the LT and RT modifiers together on the same single line item is incorrect and will typically result in a claim denial. Modifiers LT and RT should instead be used to identify paired organs, like the lungs or ovaries, and are not intended to replace Modifier 50 when a procedure is performed bilaterally during the same session, unless the payer specifically mandates the two-line approach.
Scenarios Where Laterality Modifiers Are Not Used
Laterality modifiers are designed for paired anatomical structures. Their use is inappropriate for procedures on organs or body parts that are singular or exist at the midline. Procedures performed on structures such as the heart, the spine, the esophagus, or the nasal septum should not have Modifiers LT or RT appended. Similarly, services performed through a midline incision are not considered side-specific and do not require these lateral indicators.
Laterality modifiers are also redundant or prohibited when the procedure code description already specifies the location or laterality. For instance, a CPT code that includes the word “bilateral” or “unilateral” in its definition already provides the necessary information to the payer. Codes designated as inherently bilateral by the Centers for Medicare & Medicaid Services (CMS) or the National Correct Coding Initiative (NCCI) also do not require LT or RT, as the code itself already accounts for the procedure being performed on both sides. Checking these payer lists is a necessary step to avoid overusing the modifiers, which can lead to payment issues.