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  1. What are the most common causes of leukocytosis in the hospital inpatient setting?

  2. Which medications can cause neutropenia and agranulocytosis?

  3. What are the most common causes of eosinophilia?

  4. What key white blood cell (WBC) findings indicate an impending medical emergency and warrant immediate action?

  5. What are the indications for a bone marrow biopsy and aspirate?

  6. What is the role of molecular testing in the diagnostic work up of common WBC disorders?

  7. What is the role for granulocyte colony-stimulating factors (GCSF) in nonmalignant hematologic disorders?

Deviation from the normal range in the leukocyte count is one of the most common laboratory abnormalities in the inpatient setting and frequently indicates the onset of clinical conditions that significantly impact hospitalized patients. Individual laboratory values may vary from day to day depending on fluid status and other factors. Hence, a “normal” white blood cell (WBC) or differential count has a typical distribution of values (Table 174-1).

Table 174-1 The Normal White Blood Cell Count

A natural response to the physiologic fluctuations of the host's hormonal and cytokine milieu, WBC counts also vary with the time of day and the season of the year. Typically, the hormonal variation associated with pregnancy will also increase the absolute WBC count due to an increase in circulating neutrophils.

There is also a significant genetic component to the ranges expressed on a WBC count, as neutrophil counts have been shown to vary considerably among ethnic groups. People of African descent, Yemenite and Ethiopian Jews, and people of Middle Eastern decent all have been shown to possess WBC counts with medians well below those established in predominantly Caucasian populations. Typically, these values do not fall below the threshold of mild neutropenia (< 1.5 × 109) for any significant period of time, and thus are not usually associated with significant infection risk. In fact, these physiologic deviations are not known to result in any clinically measurable increase in morbidity or mortality, and do not require any specific intervention once underlying pathology has been ruled out.

Recognizing abnormalities of the complete blood count (CBC) and, more specifically, the composition of the differential count are critical for formulating a differential diagnosis of disorders involving the WBC lineages. Valuable time and resources can be saved and best directed if careful attention is paid to these simple tests in the context of a good history and physical examination performed when abnormalities are first detected. As a general rule of thumb, malignant causes should always be considered in the differential diagnosis when red blood cell (RBC) or platelet lineages are ...

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