FHW4 on CBC Manual Differential: Not a Standard Result Code
FHW4 is not a recognized or standard result code in Complete Blood Count (CBC) manual differential reporting, and does not appear in any established hematology guidelines, laboratory standards, or clinical practice recommendations.
What FHW4 Likely Represents
This appears to be either:
- A laboratory-specific flag or internal code that varies by institution 1
- An instrument-specific notation from a particular automated hematology analyzer 2
- A data entry or transcription error that should be clarified with the reporting laboratory 1
Standard CBC Manual Differential Components
According to established laboratory practice, a proper CBC manual differential should report 3, 1:
- White blood cell (WBC) count with absolute values 3
- Neutrophils (segmented and band forms) as percentage and absolute count 4
- Lymphocytes as percentage and absolute count 5
- Monocytes as percentage and absolute count 5
- Eosinophils as percentage and absolute count 5
- Basophils as percentage and absolute count 5
- Immature forms (bands, metamyelocytes, myelocytes) when present 4
Recommended Action
Contact the laboratory immediately to clarify what FHW4 represents in their specific reporting system 1. Different laboratories use varying internal codes and flags that are not standardized across institutions 2, 1.
Important Clinical Context
When reviewing CBC results with manual differential 4, 6:
- Manual differential is essential for accurately assessing band forms and immature neutrophils, which automated analyzers frequently miss 4, 7
- Left shift indicators (band count ≥1,500 cells/mm³ or ≥16% bands) have significant diagnostic value for bacterial infection 4
- Clinical correlation is always required—laboratory values must be interpreted with clinical presentation, not in isolation 6
The International Consensus Group for Hematology Review has established 41 standardized rules for automated CBC interpretation, but these do not include any "FHW4" designation 1.