A CPT code is the five-character identifier for a specific medical service: this scan of this body part with or without contrast, this length of psychotherapy session, this complexity of office visit, this repair of this length in this location.

It is the unit that the entire billing system runs on. A hospital’s published price file is organised by it, an insurer’s negotiated rate is attached to it, and a prior authorization is granted for it. Everything downstream of the code is arithmetic.

For a patient this has one enormous practical consequence: without the code, you cannot get a comparable price. “How much is an MRI” produces a number for a different study than the one you are having. “How much is CPT 70553” produces a number for yours. The ordering office has the code, it takes them a minute to look up, and almost nobody asks for it.

In New York: the code is what makes the state’s price transparency infrastructure usable. Every hospital is required to publish a machine-readable file of its standard charges, including the cash price and negotiated rates, and those files are indexed by code. With the code you can look up your own hospital’s published price for exactly what you are scheduled for. Without it, the file is a spreadsheet of thousands of rows about other people’s care. How to read a price file.

The code also matters after the fact. An explanation of benefits lists codes, and comparing them against what you were told was ordered is how you find a service billed that never happened.

The three-call script it unlocks: ask the ordering office for the code, ask the facility for the cash price for that code and whether it includes the professional fee, ask your plan how that code applies to your deductible.

Also called: procedure code, billing code, service code. Full guide: What it costs, and how to get a real number.

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This page explains how the system works. It is not medical advice. More.