Absolute Accuracy

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.

Continued on page 2

Identify the Human Barriers

Generalists and hematologists with decades of experience will have percentage differentials embedded in imagination and habits more than some physicians. To build an action plan that succeeds, you’ll need to consider all human barriers.

A structured team approach can identify many of these human and cultural barriers. Ask your employees to brainstorm objections to this change. Involving your staff early helps generate enthusiasm to strengthen your vision (V) and thus dissatisfaction (D) with the status quo. Here are suggested questions for discussion:

? Why is this considered a barrier?

? What impact does it have (major or minor)?

? How likely is it to occur (unlikely or likely)?

? What can the lab do to remove it?

? When should the lab do this?

? Who should lead different parts of the project?

This and a prioritization system listed in Table 2 (scoring added) are suggested by one industry quality web site.4 Ask people for their instinctive reactions to change. This can include responses such as “If no one has complained, why are we changing?” to “We don’t have the power to change.”

Table 2

Rank Ordering Human Barriers to Change
How likely is it?
Unlikely (-1) Likely (+2)
If it did occur it would be Major objection (+1) 0 3
Minor objection (-1) -2 1

Action Planning

A team approach to identify barriers creates dissatisfaction (D) and clarifies vision (V). This process also identifies first steps (F) that can be taken, crucial to overcoming resistance (R). Building your action plan to account for resistance increases your chance of success.

Steps, such as changing the report formatting and sending a memo to physicians, are embedded in a description of the proposed change. Others, such as Physician A in the ED insists on manual differentials or Tech A is a constant complainer whenever anything changes, may arise in discussion. All should be addressed by your action plan.

A partial sample action plan is listed in Table 3 that illustrates when and how human barriers are linked to steps. Adding your score highlights obstacles that can require extra effort to overcome. Additional columns in your action plan include action taken, resources needed for the action, who is responsible, and a deadline date.

Table 3

Sample Action Plan
Step Barrier(s) Score
Educate staff

Old habits are hard to break
Per diem techs need to be trained
Off shift techs need to be trained
Techs uncomfortable with calculating absolute counts from a manual differential

Educate physicians

Old habits are hard to break
Physicians may not agree to change
Our pediatrician wants percentage diffs
Outliers may demand percentages
Office staff participation varies

Recruit staff champion Will encounter staff resistance
Need an incentive
Recruit physician champion Physician buy-in is unknown (do we need a champion?) ???
Draft format change Not aware of what physicians want to see
Smear review reflex criteria may be different
Test format change Lack of participation or interest 0
Develop system backup Solution may seen complicated
Techs less comfortable with computers will revert to reporting percentages
Develop assurance tool Lack of participation or interest 0
Implement new format Lack of communication
System downtime while change is made
Track outliers Physicians demanding the “old format”
Lack of communication
Sustain new behavior Not educating new staff
Reverting to old habits

Inertia of physician and laboratory cultures can seem to overwhelm efforts to change your CBC to report an absolute instead of a percentage differential. By identifying and building your action steps around human barriers, you can make this change. As a result your laboratory will report more accurate values that lead to better patient care.

Scott Warner, MLT(ASCP) is lab manager at Penobscot Valley Hospital in Lincoln, ME.


1. Zwick D. WBC leukocyte differential data processing. Pathology and Laboratory Medicine News (July 2009). Available at: http://www.childrensmercy.org/Content/uploadedFiles/Departments/Pathology_and_Laboratory_Medicine/News0709-Dr.%20Zwick.pdf. Last accessed: 7/1/11.

2. Etzell J. For WBC differentials, report in absolute numbers. Available at: http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt{actionForm.contentReference}=cap_today%2F0310%2F0310d_for_wbc_differentials.html&_state=maximized&_pageLabel=cntvwr. Last accessed: 7/1/11.

3. Value Based Management. Change Equation – Beckhard. Available at: http://www.valuebasedmanagement.net/methods_beckhard_change_model.html. Last accessed: 7/2/11.

4. NHS Institute for Innovation and Improvement. Human barriers to change. Available at: http://www.institute.nhs.uk/quality_and_service_improvement_tools/quality_and_service_improvement_tools/human_dimensions_-_human_barriers_to_change.html. Last accessed: 7/2/11.

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