Measurement of inorganic phosphorus (phosphate) in blood, used in metabolic bone disease, renal, and nutritional workups.
- Medicare
- $0.00
- Work RVU
- 0
- Global, days
- Region
- General
Documentation requirements
What must appear in the operative or office note to support the claim.
Source · Editorial brief grounded in 3 cited references ↓
- Clinical concern for metabolic bone disease, nonunion, or nutrition
- Diagnosis linked to that concern
- Related labs ordered, such as calcium and vitamin D
- Confirmation that a full panel was not run
- Lab report with phosphorus result
Applicable modifiers
Modifiers commonly billed with this code.
Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual
What this code covers
Source · Editorial summary grounded in 3 cited references ↓
Phosphorus (84100) gets ordered when the bone itself looks wrong: suspected osteomalacia, a nonunion that will not heal, a stress fracture in a young patient with poor nutrition, or a child with bowing and suspected rickets. Phosphorus, calcium, alkaline phosphatase, PTH, and vitamin D together tell you whether bone is mineralizing.
Phosphorus is a component of the renal function panel but not of the BMP or CMP. If you order a CMP and phosphorus, bill both. If the lab runs every component of the renal function panel, the panel code is required instead of the individual tests. That panel rule catches offices that build their own lab order sets.
The diagnosis needs to reflect the concern: osteomalacia, delayed union, malnutrition, chronic kidney disease, or a vitamin D disorder. Payers deny phosphorus tied to a simple sprain or routine post-op visit.
RVU & reimbursement
Component RVUs and Medicare national rate. Actual payment varies by GPCI locality.
Source · CMS Physician Fee Schedule, RVU26A · January 2026
| Work RVU | 0 |
| Practice expense RVU | 0 |
| Malpractice RVU | 0 |
| Total RVU | 0 |
| Medicare national rate | $0.00 |
| Global period | days |
Payment by site of service
Medicare pays different rates by setting. HOPD typically pays substantially more than ASC for the same procedure.
Source · CMS OPPS Addendum B·ASC HCPCS payment rates·2026
| Setting | Medicare rate (national) |
|---|---|
Office (PFS non-facility) Procedure performed in physician's office | $0.00 |
Common denial reasons
The recurring reasons claims for CPT 84100 get rejected.
Source · Editorial brief grounded in CMS NCCI edits, AAOS coding appeals, and cited references ↓
- All renal function panel components billed individually
- Diagnosis limited to routine aftercare
- Frequency beyond payer policy
- Duplicate claim with reference lab
- Screening indication without coverage
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 3 cited references ↓
01Is phosphorus part of a CMP?
02When do ortho surgeons order phosphorus?
03Can I bill phosphorus and calcium separately?
Sources & references
Editorial content was developed using the following public sources.
Mira Scribe
Mira Scribe captures the reason the surgeon suspects a mineralization problem, such as a stalled union, so the phosphorus order has its justification on file.
See how Mira captures CPT 84100 documentation