Every charge on your hospital bill is represented by a code. CPT codes (Current Procedural Terminology) describe what was done to you. ICD-10 codes describe why it was done. Understanding these codes — even at a basic level — transforms you from a confused patient into someone who can actually verify their bill. Here's the plain-English guide.
CPT codes are five-digit numeric codes published by the American Medical Association that identify every medical procedure, service, and test. They're the universal language of medical billing — when a hospital bills your insurer, they use CPT codes to describe what they did. Every CPT code has a corresponding relative value unit (RVU) that determines how much Medicare pays for it, which becomes the baseline for all other pricing.
When you see a number like 99285 on your bill, that's a CPT code. Specifically, 99285 is the code for a Level 5 emergency department visit — the highest complexity level, which costs $1,500–$2,500 and should only be assigned to the most complex cases.
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Check my bill free →These are the codes for office visits, emergency department visits, and hospital care. They're the most commonly upcoded codes in medical billing.
If you had a straightforward visit but your bill shows a Level 4 or Level 5 code, ask for the documentation that justifies that level — specifically the medical decision-making documentation.
Each surgical procedure has its own CPT code. The key thing to know: many procedures include follow-up care in the same code through what's called the "global surgical package." Billing separately for a post-op visit that's included in the global package is an unbundling violation.
Blood tests, urinalysis, cultures, and pathology exams all have specific codes. Duplicates are extremely common — the same test code appearing twice on the same date is a clear billing error.
Key codes to recognize:
Imaging studies. High-dollar codes to recognize:
ICD-10-CM codes (International Classification of Diseases, 10th Revision) describe the diagnosis — the reason for the visit or the condition being treated. They affect coverage directly. A preventive service coded with the right ICD-10 code is free under the ACA. The same service coded with a diagnostic ICD-10 code subjects you to your full deductible.
Examples:
If your annual physical was coded with a diagnostic code instead of the preventive code Z00.00, you may have been charged for a visit that should have been free.
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Check my bill free →Request an itemized bill specifically. Ask the billing department for an "itemized statement" that shows the CPT code for every service, not just the description. You have the right to receive this.
For E/M codes specifically, the level billed must match the complexity documented in the physician's note. If your visit was routine and a Level 4 or 5 code was billed, request the physician's note and look for the medical decision-making section — it should document high complexity. If it doesn't, the code is unsupported. A certified professional coder (CPC) can review your records and bill for a definitive opinion.
An NPI (National Provider Identifier) is a unique 10-digit number assigned to every healthcare provider. Your bill should show the NPI of the provider who treated you. You can look up any NPI at nppes.cms.hhs.gov to verify the provider's name, specialty, and whether they're enrolled in Medicare — all relevant if you're disputing an assignment violation.