From the Guidelines
The discrepancy between the automated and manual differential counts is clinically significant and warrants further investigation to determine the accurate neutrophil count. I recommend repeating the complete blood count with manual differential to confirm these values, as suggested by the Infectious Diseases Society of America in their 2008 update 1. This discrepancy likely indicates either a laboratory error or the presence of abnormal white blood cells that the automated analyzer is misclassifying. Automated analyzers sometimes misidentify immature neutrophils, abnormal lymphocytes, or blasts as mature neutrophils. The lower neutrophil count on manual differential (0.8) suggests neutropenia, which could indicate bone marrow suppression, infection, medication effect, or hematologic disorder. Key points to consider in the investigation include:
- The presence of an elevated WBC count or a left shift, which warrants a careful assessment for bacterial infection 1
- The importance of monitoring the patient for signs of infection, such as fever or localized symptoms, especially if they are immunocompromised
- The manual differential is generally considered more accurate when discrepancies exist because it involves direct microscopic examination by a trained laboratory professional who can properly identify abnormal or immature cells that automated systems might miscategorize. In terms of variability, studies have shown that the analytic variability in determining the WBC count using an automated leukocyte counter ranges from 2.2% to 7.7% and from 9.3% to 17.6% using a hemocytometer 1. However, the most recent and highest quality study 1 prioritizes the use of manual differential counts in the evaluation of suspected infection, particularly in older adult residents of long-term care facilities. Therefore, repeating the complete blood count with manual differential is the recommended course of action to ensure accurate diagnosis and appropriate management.
From the Research
Automated vs Manual Differential Leukocyte Counts
- The study 2 found that using manual microscopic examination as a validation procedure rather than as a reflexive substitute for automated methods can optimize patient care and laboratory operations.
- Automated differential leukocyte counts are widely accepted in routine practice, but many laboratories still perform manual counts based solely on abnormal automated results or instrument "flags" 2.
- The use of automated differential counts can decrease turnaround time for results, be less expensive, and reduce exposure of technologists to direct contact with patients' blood 3.
- However, automated instruments may fail to detect patients' blood samples with small numbers of abnormal cells, such as blasts in early relapse of acute leukemia or atypical lymphocytes in viral diseases 3.
Discrepancies between Automated and Manual Diff
- The discrepancy between automated and manual differential leukocyte counts, such as ne# 1.60 and segabs 0.8, may be due to the limitations of automated instruments in detecting abnormal cells 3.
- Manual differential counts may be necessary to confirm or obtain additional information on selected cases, especially in patients with hematologic abnormalities 4.
- The routine eye-count differential method lacks both sensitivity and specificity, and automated differential leukocyte instruments can address many of the technique- and method-related errors 5.
Clinical Implications
- Clinical judgment should be used in selectively ordering manual differential counts for patients with suspected hematologic abnormalities 3.
- Automated differential counts can be useful in screening general medical and surgical patients, but manual differential counts and further examination of a smear may be necessary in referral centers where hematologic abnormalities are more prevalent 3.
- The correlation of clinical disease with automated differential counts requires further study to improve efficiency, economy, and safety while not compromising patient care 3.