Interpretation of Complete Blood Count Results

Red Blood Cell Parameters

The National Comprehensive Cancer Network recommends evaluating hemoglobin and hematocrit to assess oxygen-carrying capacity, with abnormalities indicating anemia, polycythemia, or dehydration 1
The National Comprehensive Cancer Network suggests using Mean Corpuscular Volume (MCV) to classify anemia as microcytic, normocytic, or macrocytic 1
A low reticulocyte index indicates decreased red blood cell production, while a high index suggests blood loss or hemolysis 1

The Infectious Diseases Society of America recommends assessing total white blood cell count for leukocytosis or leukopenia 2
The Infectious Diseases Society of America suggests that neutrophilia with left shift strongly indicates bacterial infection, with a likelihood ratio of 14.5 for band count >1,500 cells/mm³ 2
The Society for Immunotherapy of Cancer notes that lymphocytosis may indicate viral infection, and eosinophilia suggests allergic or parasitic conditions 3

The Society for Immunotherapy of Cancer recommends assessing platelet count for thrombocytopenia or thrombocytosis 3
The Society for Immunotherapy of Cancer suggests considering potential causes of thrombocytopenia, including bone marrow suppression, immune destruction, or consumption 3

The Centers for Disease Control and Prevention recommends reporting both percentages and absolute counts for immunophenotyping results 4, 5
The Centers for Disease Control and Prevention suggests including both percentage and absolute number when reporting CD4+ T-cell counts 5

The Centers for Disease Control and Prevention warns against failing to correct for lymphocyte purity when reporting immunophenotyping results 4
The Infectious Diseases Society of America advises against overlooking the significance of left shift even in the absence of leukocytosis 2
The Infectious Diseases Society of America recommends avoiding ordering additional tests when results will not change management decisions 2

Severe neutropenia (<500 cells/mm³) indicates high infection risk requiring urgent evaluation, according to the American Academy of Allergy, Asthma, and Immunology 6
In infants, severe lymphopenia (<2,500 cells/mm³) should prompt evaluation for severe combined immunodeficiency (SCID), especially if accompanied by absent thymus on imaging, as recommended by the American Academy of Allergy, Asthma, and Immunology 6

Platelet count >400,000/μL in giant cell arteritis has a positive likelihood ratio of 3.75 for diagnosis, as reported by the American Medical Association 7

For research protocols, obtain CBC within 48 hours of enrollment, including WBC with differential (percent and absolute lymphocytes/prolymphocytes), hemoglobin, hematocrit, platelet count, and reticulocyte count, as recommended by the National Comprehensive Cancer Network 8, 9
Repeat CBC at appropriate intervals to assess treatment response, as suggested by the National Comprehensive Cancer Network 8, 9
In chronic lymphocytic leukemia evaluation, hemoglobin should be measured alongside immunoglobulin levels and direct/indirect Coombs testing, according to the American Society of Hematology 8
In multiple myeloma workup, obtain CBC with differential and platelets alongside BUN, creatinine, calcium, and albumin, as recommended by the National Comprehensive Cancer Network 9