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INTRODUCTION

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CASE HISTORY • Part 1

A 50-year-old man presents with a history of worsening headaches, difficulty sleeping, and general malaise. Past history is positive for hypertension, chronic obstructive pulmonary disease, and a recent deep venous thrombosis. He has a more than 30-year history of smoking and poor weight control. Examination reveals an obese male (~280 lbs) with a ruddy complexion. Vital signs: BP - 160/95 mm Hg; P - 94 bpm; R - 18 bpm. Otherwise, his examination is unremarkable.

CBC: Hematocrit/hemoglobin - 59%/19.7 g/dL

MCV - 92 fL  MCH - 32 pg  MCHC - 33 g/dL

RDW-CV - 12%

WBC count - 14,500/μL

Platelet count - 280,000/μL

SMEAR MORPHOLOGY

Normocytic and normochromic with normal white blood cell morphology. Platelets are abundant with some clumping.

Reticulocyte count/index - 1.0%/>1

Sedimentation rate - 10 mm/h (Westergren)

Questions
  • What CBC abnormality is apparent?

  • What tests are indicated to explore the cause?

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Erythrocytosis and polycythemia are clinical terms used to describe an abnormally elevated hemoglobin (hematocrit) or red blood cell mass. As with anemia, the probability that a patient has an elevated hemoglobin level will depend on the distribution of "normal" hemoglobin levels for any population. This will differ according to age, gender, race, and for subjects living at different altitudes (see Chapter 1). Physiological changes can also result in an apparent increase in the hemoglobin/hematocrit without a concomitant change in red cell mass. Because the hemoglobin and hematocrit are simple ratios of the concentration of red blood cells to volume of plasma, an increase can result from a reduction in plasma volume without a true increase in red blood cell mass (relative erythrocytosis).

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Detection and accurate diagnosis of erythrocytosis is important regardless of its cause. Even modest increases in the hemoglobin/hematocrit level can have a major impact on whole blood viscosity. Depending on the patient's clinical condition, an increase in the hematocrit can significantly affect blood flow and oxygen delivery to tissues. Therefore, management involves both treating the primary condition and appropriately adjusting the patient's hematocrit to normal.

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NORMAL ERYTHROPOIESIS AND BLOOD VOLUME CONTROL

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The total number of red blood cells in circulation varies according to the patient's age, gender, race, and clinical condition. Just as the erythroid marrow increases red blood cell production in response to anemia, the number of red blood cells produced each day will increase in response to chronic hypoxia. The normal value for a patient must take these factors into account. The normal distribution of hemoglobin or hematocrit measurements will be different for men and women of different ages and for individuals living at higher altitudes (Figure 13-1). In addition, patients with mild to moderate hypoxia caused by lung disease will compensate by increasing the number of circulating red blood cells. Within limits, this physiologic response to decreased oxygen availability to tissues is an effective compensatory mechanism.

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FIGURE 13-1

Hemoglobin levels at ...

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