Block 24e on the CMS-1500 form is the diagnosis pointer field. You fill it with one to four letters, A through L, that match the diagnosis codes you listed in Block 21. Each letter tells the payer which diagnosis justifies the service billed on that line, and a missing or wrong pointer is one of the most common reasons a clean-looking claim comes back denied.
What to Enter in Block 24e
Enter the reference letter from Block 21 that supports the service on that line. If more than one diagnosis applies, you can enter up to four letters, left-justified, with no commas and no spaces between them. So if diagnoses A and C both support the service, you type AC.
Do not enter the actual ICD-10-CM code in this field. Only the letters belong here. The full code stays in Block 21.
Every service line in Block 24 has its own 24e. A service line with a procedure code but no pointer is incomplete and will be rejected.
How Block 21 Feeds Block 24e
Block 24e only makes sense in relation to Block 21, so it’s worth confirming Block 21 is set up correctly before you touch the pointers.
Block 21 holds up to twelve ICD-10-CM diagnosis codes, each on its own lettered line from A through L. Enter the ICD indicator “0” in the space between the dotted lines to signal ICD-10-CM. Medicare requires the highest level of specificity available, and codes are entered without periods.
Once Block 21 is populated, Block 24e simply points back to it. Line A’s diagnosis becomes pointer “A.” Line C’s diagnosis becomes pointer “C.” The pointer is the bridge between the procedure code in 24d (what you did) and the diagnosis in Block 21 (why you did it).
Put the Primary Diagnosis First
The order of the letters in 24e is not arbitrary. Both the NUCC instructions and Medicare guidance say the diagnosis that most directly supports the service belongs first, with additional supporting diagnoses after it.
This matters because many payers run automated edits against the first-listed pointer only. If the first letter points to a diagnosis that doesn’t justify the procedure, the claim can be denied even when a valid supporting diagnosis is sitting right behind it in the sequence. Lead with the diagnosis that best establishes medical necessity for that specific service line.
Mistakes That Get Claims Denied
A few patterns account for most 24e-related rejections:
- Leaving the field blank. Any service line without a pointer comes back as unprocessable.
- Pointing to a diagnosis that doesn’t support the procedure. This triggers denial code 11, meaning the diagnosis does not match or support the service performed.
- Typing the full ICD-10-CM code into 24e instead of the reference letter. Only A through L belong in this field.
- Adding commas or spaces between letters. The NUCC requires letters entered left-justified with no separators.
- Listing the same diagnosis code twice in Block 21. Medicare Administrative Contractors return these claims as unprocessable with Claim Adjustment Reason Code 16 and Remark Code M76, both indicating missing or invalid diagnosis information.
That last one feels harmless. A biller might repeat a code across two lines in Block 21 thinking it adds clarity, but Medicare’s editing systems treat the duplication as an error and reject the whole claim.
Electronic Claims Use Numbers, Not Letters
If you’re submitting electronically rather than on paper, the equivalent of Block 24e is the SV107 segment in loop 2400 of the 837P transaction. The 837P uses numeric pointers, 1 through 12, instead of the paper form’s alphabetical A through L. Alpha pointers have to be converted to their numeric equivalents before the claim goes out.
Fixing a Pointer-Related Denial
When a claim is denied for a pointer problem, start by comparing the medical record to what was billed. Confirm that the codes in Block 21 reflect what the provider documented, then check that the pointer in 24e references the diagnosis that actually supports each service.
If it’s a data entry mistake, correct the pointer and resubmit. If the diagnosis genuinely doesn’t support the procedure, talk to the rendering provider before resubmitting. The documentation may support a more specific code that establishes medical necessity, or additional clinical notes may need to be gathered first.
Track these denials. Pointer errors tend to follow patterns, often a specific procedure code that keeps getting linked to the wrong diagnosis template in the billing software, and catching the pattern fixes more than one claim at a time.