CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
Editor: Frederick L. Kiechle, MD, PhD
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Reporting percent cell count reference ranges
Managing WBC diff 24-hour urine samples
Q. Checklist requirement HEM.23050 regarding reference intervals includes a note that if absolute cell counts are reported with their reference ranges, then percent cell count reference ranges should not be reported because they can lead to misinterpretation of CBC data. I understand that many laboratories, like ours, have been reporting reference ranges for both absolute and percent cell counts, and I would like to clarify whether this is permissible.
A. Regarding HEM.23050, currently it is strongly recommended (though not an absolute requirement) that WBC differential percent cell count reference ranges not be reported when accompanied by reporting of absolute cell counts with their reference ranges. It remains at the discretion of the laboratory as to how reference ranges are to be reported, but impact on patient care decisions at the institution should be considered.
The CAP Hematology/Clinical Microscopy Resource Committee provides the following explanation: “If absolute cell counts are reported with their reference ranges, then percent cell count reference ranges should not be reported. In this situation, reporting percentage reference intervals is discouraged because individual values regarded as normal, high, or low may be discordant with the corresponding absolute values, leading to misinterpretation of CBC data. Absolute cell count values are the clinically meaningful parameters and must be accompanied by their reference intervals.”
To illustrate the difference between results as compared with their respective reference ranges, a case example is provided below (excerpted from the March 2010 CAP TODAY article “For WBC differentials, report in absolute numbers”).
Mr. Jones is a 54-year-old man with a fever and fatigue. The CBC shows a WBC of 2.0 × 109/L with the following differential:
- Neutrophils 40% (40–70%)
- Lymphocytes 50% (15–45%)
- Monocytes 10% (0–12%)
- Eosinophils 0% (0–7%)
- Basophils 0% (0–2%)
Based on review of this proportional differential and its associated reference ranges, one could conclude the patient has lymphocytosis (albeit relative) and pursue diagnostic considerations based on this result. Many of us have been witness to clinical conversations similar to this. If these differential results are converted to absolute values, the following data would be more appropriately evaluated: