Differential Diagnosis for Elevated WBC and Abnormal Cell Counts

Given the patient's lab results (WBC 15,486, RBC 4,970, Poly 25%, Mononuclear 75%), the following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Viral Infection: The high percentage of mononuclear cells (75%) suggests a viral infection. Viral infections often cause an increase in mononuclear cells, such as lymphocytes and monocytes, in response to the infection.
• Other Likely Diagnoses
  • Bacterial Infection: Although the percentage of polymorphonuclear cells (PMNs or polys) is lower than expected for a typical bacterial infection, some bacterial infections can present with a mixed picture, especially in the early stages or in certain types of infections.
  • Chronic Inflammatory Condition: Conditions like chronic inflammatory bowel disease or rheumatologic diseases can cause an elevation in WBC count with a variation in the differential count.
• Do Not Miss Diagnoses
  • Severe Bacterial Sepsis: Even though the polys percentage is low, sepsis can present atypically, especially in elderly or immunocompromised patients. Sepsis is a life-threatening condition that requires immediate attention.
  • Malignancy: Certain types of leukemia or lymphoma can cause an abnormal WBC count and differential. These conditions are critical to diagnose early for appropriate management.
• Rare Diagnoses
  • Parasitic Infection: Some parasitic infections can cause an increase in eosinophils, a type of white blood cell, but the provided differential does not specify eosinophil count. However, parasitic infections can sometimes present with a mixed or atypical differential count.
  • Histiocytosis: A rare group of diseases involving abnormal proliferation of histiocytes, which can affect various organs and present with a range of symptoms, including abnormal blood cell counts.

Consideration for Peritonitis

Peritonitis, which is inflammation of the peritoneum, typically presents with abdominal pain, fever, and signs of infection. The diagnosis of peritonitis is more clinical and requires evidence of peritoneal irritation (e.g., rebound tenderness) and possibly imaging or lab findings indicative of infection or inflammation within the abdominal cavity. While the provided lab results indicate an infection or inflammatory process, they do not specifically diagnose peritonitis without additional clinical context.

It's crucial to correlate these lab findings with clinical symptoms, physical examination, and possibly additional diagnostic tests to determine the underlying cause accurately.