Hi - Have you tried checking the interventional radiology or cardiology forums? Perhaps someone there will have some specialty insights to help for the specific case. In general terms, 36466-LT, 36465-RT represent two veins in the left and one vein on the right.
For instance the WPS LCA (
Article - Billing and Coding: Treatment of Varicose Veins of the Lower Extremities (A56914)) has this for opposite legs:
"When reporting
sclerotherapy procedures (36465, 36466, 36470, and 36471) performed on opposite legs, report CPT code 36465, 36470 (one vein) and 36466, 36471(multiple veins) on separate lines using the RT and LT modifiers. For bilateral services, use the 50 modifier. Only one service should be reported for each leg regardless of how many veins are treated. When the procedure is performed for cosmetic purposes, use code Z41.1."
CPT Assistant (Dec. 2018) says 36465 and 36466 "may be reported for lower extremity truncal veins that include the great saphenous vein (GSV; also called the long saphenous); the small saphenous vein (SSV; also called the short saphenous); the anterior and posterior accessory of the great saphenous vein (AAGSV, PAGSV); and the extension of the SSV termed the intersaphenous vein (Vein of Giacomini). Codes 36465 and 36466 may not be reported for perforators or saphenous tributaries (sometimes called “branch veins”) because they are not one of the truncal veins listed previously."