Differential Diagnosis for Low WBC and High Mono Lab
- Single Most Likely Diagnosis
- Viral infection (e.g., mononucleosis, influenza): This is the most likely diagnosis due to the presence of a high monocyte count, which is often seen in viral infections. The low WBC count may be due to a relative lymphopenia or a bone marrow suppressive effect of the virus.
- Other Likely Diagnoses
- Bacterial infection (e.g., tuberculosis, brucellosis): Certain bacterial infections can cause a high monocyte count and a low WBC count, especially if the infection is chronic or severe.
- Autoimmune disorders (e.g., lupus, rheumatoid arthritis): Some autoimmune disorders can cause a low WBC count and an elevated monocyte count due to chronic inflammation and immune system dysregulation.
- Medication effect (e.g., chemotherapy, immunosuppressants): Certain medications can suppress the bone marrow, leading to a low WBC count, and cause an increase in monocytes as a response to the medication-induced stress.
- Do Not Miss Diagnoses
- Leukemia (e.g., acute lymphoblastic leukemia, chronic lymphocytic leukemia): Although less likely, leukemia can cause a low WBC count and an elevated monocyte count, and missing this diagnosis can be fatal if left untreated.
- Aplastic anemia: This rare condition can cause a low WBC count due to bone marrow failure, and an elevated monocyte count may be seen as a response to the underlying inflammation.
- Sepsis: In severe cases of sepsis, the WBC count can be low due to bone marrow suppression or consumption of white blood cells, and an elevated monocyte count may be seen as a response to the infection.
- Rare Diagnoses
- Lymphoma: Certain types of lymphoma can cause a low WBC count and an elevated monocyte count, although this is less common.
- Myelodysplastic syndrome: This group of disorders can cause a low WBC count and an elevated monocyte count due to bone marrow dysplasia and ineffective hematopoiesis.
- Histiocytosis: Rare conditions like Langerhans cell histiocytosis can cause a low WBC count and an elevated monocyte count due to infiltration of the bone marrow by histiocytes.