What is the further workup for a patient with a white blood cell (WBC) count of 6.4 x10^9/L, monocytosis (15.4% with an absolute monocyte count of 0.99 x10^9/L), and eosinophilia (9.5% with an absolute eosinophil count of 0.61 x10^9/L)?

From the Guidelines

No further workup is necessary for these lab values as they are within or near normal ranges. The total white blood cell count of 6.4 x 10^9/L is within normal limits (typically 4.5-11.0 x 10^9/L). While the monocyte percentage is slightly elevated at 15.4% (normal range typically 2-10%), the absolute monocyte count of 0.99 x 10^9/L is just at the upper limit of normal (typically 0.2-1.0 x 10^9/L). Similarly, the eosinophil percentage is elevated at 9.5% (normal range 1-6%), but the absolute count of 0.61 x 10^9/L is only mildly elevated (normal range typically 0.0-0.5 x 10^9/L). These mild elevations in monocytes and eosinophils with normal neutrophils and lymphocytes often represent a normal physiologic response to recent infection, allergic reaction, or medication effect rather than a pathologic process, as noted in the guidelines for myeloid/lymphoid neoplasms with eosinophilia and tk fusion genes 1. If the patient is asymptomatic, observation with possible repeat testing in 4-6 weeks would be reasonable to ensure these values normalize. However, if the patient has persistent symptoms such as fatigue, recurrent infections, or other concerning findings, further evaluation might include a thorough history and physical examination focusing on potential causes of monocytosis and eosinophilia, and consideration of additional laboratory testing as outlined in the guidelines, including serum tryptase levels, and vitamin B12 levels, as well as a peripheral blood smear to review for other blood count abnormalities 1. Some potential causes of these lab findings could be explored through serology testing for Strongyloides and other parasitic infections, testing for antineutrophil cytoplasmic antibodies and antinuclear antibodies, or quantitative serum immunoglobulin levels (including IgE) 1. But given the mild nature of the elevations and the absence of other concerning findings, a more extensive workup is not initially warranted.

From the Research

Monocytosis and Eosinophilia Workup

• A white blood cell (WBC) count of 6.4 with a monocyte percentage of 15.4% and an absolute monocyte count of 0.99, along with eosinophilia (9.5% and absolute count of 0.61), may require further investigation 2, 3.
• The presence of monocytosis can be caused by a wide variety of neoplastic and non-neoplastic conditions, and its evaluation involves integrating laboratory data, morphology, clinical findings, and ancillary studies 2.
• Eosinophilia can be associated with various conditions, including primary biliary cirrhosis (PBC) 4, and chronic myeloid leukemia (CML) 5.
• A stepwise diagnostic approach for monocytosis includes basic studies, flow cytometry, and other diagnostic tests to distinguish between different etiologies 3.
• The high eosinophil count in this case may warrant further investigation, including evaluating for conditions such as PBC or CML, and considering the use of ancillary studies like flow cytometry 6, 4, 5.

Potential Diagnostic Considerations

• Primary biliary cirrhosis (PBC) should be considered as a potential cause of eosinophilia, especially if liver function tests are abnormal 4.
• Chronic myeloid leukemia (CML) is another potential cause of eosinophilia and monocytosis, and should be evaluated using diagnostic tests like flow cytometry and molecular studies 5, 3.
• Other causes of monocytosis and eosinophilia, such as infections, inflammatory disorders, or other hematologic malignancies, should also be considered and investigated accordingly 2, 3.