What a unit limit does — Medically Unlikely Edit
20610Arthrocentesis / injection — major joint or bursa (knee, shoulder, hip)3 units
2 allowedcap 2/day
The claim as billed
One line: 20610, 3 units on the same day.
The same rule runs on every line of a real claim — this is one line, slowed down. A cap can also be zero: a commercial preventive physical (99396) billed to Medicare is capped at nothing, because Medicare does not cover it. Check any code under Bundling & units.