Differential Diagnosis for Elevated WBC without Infectious Source

Single Most Likely Diagnosis

• Stress or Steroid-Induced Leukocytosis: This condition is a common cause of elevated white blood cell (WBC) count without an apparent infectious source. Stress, whether physical or emotional, and the use of corticosteroids can lead to an increase in WBCs due to the demargination of cells from the endothelium and an increase in the release of mature cells from the bone marrow.

Other Likely Diagnoses

• Chronic Myeloid Leukemia (CML): A type of cancer that affects the white blood cells and tends to progress slowly over time. It can present with an elevated WBC count without an infectious source, often discovered incidentally.
• Polycythemia Vera: A myeloproliferative disorder characterized by the excessive production of red blood cells, white blood cells, and platelets. An elevated WBC count can be a presenting feature.
• Reactive Leukocytosis due to Inflammation: Conditions such as rheumatoid arthritis, inflammatory bowel disease, or other autoimmune diseases can cause an elevation in WBC count as part of the body's inflammatory response.
• Smoking: Chronic smoking can lead to a mild increase in WBC count, likely due to the body's response to chronic inflammation and oxidative stress.

Do Not Miss Diagnoses

• Acute Myeloid Leukemia (AML): A rapidly progressing cancer of the blood and bone marrow. It requires immediate diagnosis and treatment, as delays can be fatal.
• Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with an elevated WBC count among other symptoms. Early diagnosis is crucial for effective treatment.
• Sepsis with an Unidentified Source: Although the question specifies "without infectious source," it's critical to thoroughly investigate for any hidden or atypical infections, as sepsis can be life-threatening and may not always present with typical signs of infection.

Rare Diagnoses

• Myeloproliferative Neoplasms (e.g., Essential Thrombocythemia, Primary Myelofibrosis): These are rare disorders of the bone marrow in which excess cells are produced. They can present with elevated WBC counts among other abnormalities.
• Leukocyte Adhesion Deficiency (LAD): A rare immunodeficiency disorder characterized by the inability of leukocytes to migrate to sites of infection, leading to recurrent infections and potentially elevated WBC counts due to the body's attempt to compensate for the defect.
• Chronic Neutrophilic Leukemia: A rare form of leukemia characterized by sustained neutrophilia in the absence of another identifiable cause.