Differential Diagnosis

The patient's presentation includes a history of rheumatoid arthritis, slightly abnormal CBC results (elevated white blood cells, slightly low red blood cells, elevated neutrophil count, low lymphocyte count, and elevated basophil count). Considering these factors, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Infection: Given the elevated white blood cell count (11.66) and neutrophil count (9.82), an infection is a strong consideration. The patient's history of rheumatoid arthritis may also predispose her to infections due to either the disease itself or the immunosuppressive treatments she might be on.

• Other Likely Diagnoses

  • Rheumatoid Arthritis Flare: The patient's history of rheumatoid arthritis and the current lab findings could indicate a flare of her disease, which can cause elevated inflammatory markers and changes in blood cell counts.
  • Medication Side Effects: Certain medications used to treat rheumatoid arthritis can affect blood cell counts. For example, some disease-modifying antirheumatic drugs (DMARDs) can cause leukopenia or other hematologic abnormalities.
  • Chronic Inflammation: Chronic inflammatory conditions, including rheumatoid arthritis itself, can lead to changes in blood cell counts, including anemia of chronic disease (which could explain the slightly low red blood cell count).

• Do Not Miss Diagnoses

  • Severe Infection or Sepsis: Although the patient's white blood cell count is elevated, indicating an infection, it's crucial not to miss the possibility of a severe infection or sepsis, especially in someone with a chronic condition like rheumatoid arthritis who may be on immunosuppressive therapy.
  • Hematologic Malignancy: While less likely, an elevated white blood cell count, especially with abnormalities in other cell lines (like low lymphocytes and elevated basophils), warrants consideration of a hematologic malignancy, such as leukemia.
  • Drug-Induced Agranulocytosis or Aplastic Anemia: Certain medications can cause severe drops in blood cell counts, which would be a medical emergency.

• Rare Diagnoses

  • Myeloproliferative Neoplasm (MPN): The elevation in basophils, although mild, could suggest a myeloproliferative neoplasm, a group of diseases that affect blood cell production in the bone marrow.
  • Systemic Mastocytosis: Elevated basophil count could also be seen in systemic mastocytosis, a condition characterized by the proliferation and accumulation of mast cells in various organs.
  • Other Rare Inflammatory or Autoimmune Conditions: There are several rare inflammatory or autoimmune conditions that could potentially explain the patient's lab findings, though these would be less likely without additional specific symptoms or findings.