Editors: Olga Pozdnyakova, MD, PhD, Geoffrey Wool, MD, PhD, David Bernard, MD, PhD & Raul S. Gonzalez, MD
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Q. Is it important to perform a manual differential on a CBC with a very low or very high mean corpuscular volume (MCV) result, or will a smear review/scan for RBC morphology suffice?
A. April 2025—An MCV indicates the average size of RBCs in a given sample. It is used with other RBC indices to categorize anemias based on cell size (e.g. microcytic, normocytic, and macrocytic).
A microscopic examination of the peripheral blood smear can confirm the results from the analyzer and/or identify factors that may be causing spurious results. For example, excess serum immunoglobulins (in the setting of cold agglutinin disease, multiple myeloma, etc.) or excess fibrinogen (as seen in disseminated intravascular coagulation) can produce an artifactually elevated MCV due to RBC agglutinates. Conversely, when blood samples are cold, immunoglobulins and fibrinogen can precipitate, which can lead to falsely low MCV. A hypoosmolar environment, as with hyponatremia, allows RBCs to increase their cytoplasmic water content, which can also lead to falsely low MCV. Prewarming the sample to 37°C can correct this.
RBC agglutinates and precipitants (e.g. fibrin strands, cryoglobulins, immunoglobulins) are identified by a blood smear review/scan and could prompt an immediate reanalysis of the sample. In the absence of other RBC flags, a smear review/scan is typically sufficient for confirming MCV results.
Without an identifiable cause for an elevated (macrocytosis) or decreased (microcytosis) MCV, a laboratorian can request a fresh sample for analysis. However, every laboratory must develop its own criteria for reviewing a blood smear and performing a manual differential as determined by the medical director.
Barnes PW, McFadden SL, Machin SJ, Simson E; International Consensus Group for Hematology. The International Consensus Group for Hematology review: suggested criteria for action following automated CBC and WBC differential analysis. Lab Hematol. 2005;11(2):83–90.
Briggs C, Culp N, Davis B, et al. ICSH guidelines for the evaluation of blood cell analysers including those used for differential leucocyte and reticulocyte counting. Int J Lab Hematol. 2014;36(6):613–627.
Gulati G, Song J, Florea AD, Gong J. Purpose and criteria for blood smear scan, blood smear examination, and blood smear review. Ann Lab Med. 2013;33(1):1–7.
Gulati G, Uppal G, Gong J. Unreliable automated complete blood count results: causes, recognition, and resolution. Ann Lab Med. 2022;42(5):515–530.
Julie A. Rosser, DO
Pathologist
Presbyterian/St. Luke’s Medical Center
Denver, Colo.
Member, CAP Hematology/Clinical Microscopy Committee
Q. Do exact formalin fixation times and cold ischemia times have to be listed in the final pathology report for immunohistochemistry predictive marker testing so long as they are traceable on internal records (e.g. processor times, container label times)? Or is it sufficient to state that the formalin fixation and cold ischemia times meet ASCO/CAP recommendations of less than or equal to one hour cold ischemia time and greater than six hours but less than 72 hours formalin fixation time?
The only variable not in our final reports is our end of formalin time, but it is traceable through internal laboratory records. We document in the final report the time the tissue was removed from the body and the time it was placed in formalin. Then a blanket statement of “less than or equal to one hour cold ischemia time and greater than six but less than 72 hours formalin fixation time” is inserted in the comment when it applies.
A. Stating on the report that the cold ischemia time is less than or equal to one hour and formalin fixation time is greater than six but less than 72 hours is acceptable to satisfy CAP checklist requirement ANP.22969 if the laboratory or facility submitting the specimens documents the time between removing the specimen from the patient and placing it in fixative, as required by CAP checklist requirement GEN.40115. Best practice is to document exact cold ischemia and fixation times, but if the laboratory can show with certainty that the required times were met on specimen submission, then the comment would be acceptable.
College of American Pathologists. ANP.22969 Report elements. In: Anatomic pathology checklist. Dec. 26, 2024.
College of American Pathologists. GEN.40115 Specimen collection manual elements—surgical pathology and cytopathology specimens. In: Laboratory general checklist. Dec. 26, 2024.
Collins LC, Botero ML, Schnitt SJ. Bimodal frequency distribution of estrogen receptor immunohistochemical staining results in breast cancer: an analysis of 825 cases. Am J Clin Pathol. 2005;123(1):16–20.
Fisher ER, Anderson S, Dean S, et al. Solving the dilemma of the immunohistochemical and other methods used for scoring estrogen receptor and progesterone receptor in patients with invasive breast cancer. Cancer. 2005;103(1):164–173.
Hammond ME, Hayes DF, Dowsett M, et al.; American Society of Clinical Oncology, College of American Pathologists. American Society of Clinical Oncology/College of American Pathologists guideline recommendations for immunohistochemical testing of estrogen and progesterone receptors in breast cancer (unabridged version). Arch Pathol Lab Med. 2010;134(7):e48–e72.
Wolff AC, Somerfield MR, Dowsett M, et al. Human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology–College of American Pathologists guideline update. Arch Pathol Lab Med. 2023;147(9):993–1000.
Christina Bowerman, MLS(ASCP)
Technical Specialist
Laboratory Accreditation Services
College of American Pathologists
Northfield, Ill.