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A white cell differential performed with a complete blood count (CBC) is a common test order. Doctors diagnose and track infections, leukemia and other conditions by interpreting cell lines reported as relative and/or absolute numbers. If your laboratory reports percentage numbers and your instrument reports absolutes, it may be time to upgrade your CBC to reflect your technology.
This can be a big change for your laboratory. By developing an action plan with your staff and awareness of how change will affect them, you can make the transition to reporting only absolute counts effortless.
Absolute Differences
Historically, laboratories have reported what was measured. An automated or (in the case of very low white counts) manual WBC was performed followed by a 100- or 200-cell differential. Decades of clinician experience interpreting and applying these results and their relative imprecision discouraged widespread reporting of absolute counts.
 The introduction of modern cell counters able to perform 3- and then 5-part differentials made it feasible for laboratories to report reliable absolute counts. Instead of a technologist counting 100 cells using a microscope, which is subject to variation in precision, instruments now identify and count thousands, even tens of thousands, of cells. Instruments now calculate percentage differentials based on absolute and total white cell counts.
According to David Zwick, MD, director of the Clinical Hematology Laboratory at Children's Mercy Hospital in Kansas City, Missouri, physicians prefer leukocyte percentages rather than more precise, easier to interpret absolute numbers because "dealing with percentage data is still being taught to medical students and house staff and has a firm foothold in the United States." And normal percentages, generally, are easier to remember and visualize.1
However, percentages are not only inherently inaccurate but subject to misinterpretation, since they are proportional to the total WBC. A common example is the ANC, or absolute neutrophil count, defined as the sum of segmented and banded neutrophils. Less common, perhaps, is monocytosis used as a diagnostic criteria of chronic myelomonocytic leukemia (CMML). Potential differences that may lead to unnecessary testing or misinterpretation are highlighted in Table 1.
Table 1
| Relative vs. Absolute Counts: ANC and Monocytes |
| WBC (x 103/µL) |
ANC (%) |
Monocyte (%) |
ANC (x 103/µL) |
Monocyte (x 103/µL) |
| Normal Range |
40-70 |
0-12 |
1.5-8.0 |
0.2-0.8 |
| 4.0 |
87.5 |
12.5 |
3.5 |
0.5 |
| 8.0 |
43.8 |
6.3 |
3.5 |
0.5 |
| 12.0 |
29.2 |
4.2 |
3.5 |
0.5 |
While it is recommended to report the WBC differential as absolute counts, a 2009 College of American Pathologists survey reveals that only 5.6% of laboratories comply. A small percentage of labs report both percentage and absolute numbers.2 Many laboratories in the United States continue to report WBC differentials as percentages, suggesting barriers to changing this practice.
Barriers to Change
While barriers to change may be unique to your organization, a structured approach will identify what they are to help you intervene when developing your action plan. This is an important first step, since any attempt to change behavior--in this case, techs creating new reports and doctors accepting them--will meet a natural resistance that is normal in many respects. And in this sense, it's important to consider "resistance" as information (not insubordination) that can help you succeed.
Assuming technological barriers are simpler to overcome (e.g., changing a report format in your information system), human barriers will consume most of your effort as a manager. The Beckhard and Harris "Change Equation" illustrates this point:
D x V x F > R
D = Dissatisfaction with status quo
V = Vision for change created by management
F = First steps to implement the change that are achievable
R = Resistance to change.
All three elements--dissatisfaction, vision and first steps--must be present to overcome expected resistance.3 For example, if physicians are satisfied with percentage differentials, education has to take place to strengthen a vision of quality to build dissatisfaction with the status quo.
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