Chapter 175. Quantitative Abnormalities of Platelets: Thrombocytopenia and Thrombocytosis

Thrombocytopenia

1. Does the patient have true thrombocytopenia or pseudothrombocytopenia?

2. What is the timing of onset, progression, and severity of the thrombocytopenia?

3. Is the thrombocytopenia isolated, or is there concomitant anemia, leukopenia, or both?

4. What are the findings of the peripheral blood film?

5. What tests and studies are useful to evaluate each etiology?

6. What is the frequency of specific causes of thrombocytopenia in defined clinical circumstances?

7. Is the thrombocytopenia a marker of bleeding risk, thrombosis risk, or adverse prognosis?

8. What treatments are available for each etiology?

Thrombocytosis

1. Is the thrombocytosis newly acquired during the hospitalization?

2. Is there concomitant splenomegaly and/or abnormalities in hemoglobin or white blood cell levels?

3. Does the thrombocytosis predate the hospitalization?

4. Is the red cell size (mean corpuscular volume) increased or decreased?

Introduction

The normal platelet count range is approximately 150 to 400 × 109/L (150,000 to 400,000 per mm3). An individual's platelet count usually remains relatively constant during life. The platelet count decreases normally during pregnancy (gestational thrombocytopenia). The platelet count increases to above the usual value following an acute self-limited thrombocytopenia (eg, postsurgery thrombocytosis).

Many clinicians equate thrombocytopenia with increased bleeding risk. Indeed, severe immune-mediated thrombocytopenia does pose increased bleeding risk. But certain other thrombocytopenic disorders are associated with greatly increased risk of thrombosis (eg, heparin-induced thrombocytopenia [HIT], antiphospholipid syndrome, cancer-associated hypercoagulability), or increased mortality (thrombocytopenia complicating septicemia or multi-organ system dysfunction).

The various explanations for thrombocytopenia differ depending on the clinical setting. For patients who present to the emergency room with acute, severe thrombocytopenia, certain life-threatening disorders must be considered, such as thrombotic thrombocytopenia purpura (TTP), drug-induced immune thrombocytopenic purpura (D-ITP), and acute leukemia. In postoperative patients, the timing of onset of thrombocytopenia is important since early thrombocytopenia is usually due to postoperative hemodilution, whereas later-onset thrombocytopenia suggests heparin-induced thrombocytopenia, septicemia, or other postoperative complications. Thrombocytopenia in the intensive care unit is often due to poorly defined platelet consumption complicating multiorgan system dysfunction.

The hospitalist may be the first physician called upon to evaluate a thrombocytopenic patient, especially when the platelet count decline begins during hospitalization. The hospitalist needs to appreciate the circumstances when referral to a hematologist is appropriate.

Physical Examination

The physical examination should focus on the presence of signs of bleeding (petechiae, purpura), fever, or chills (infection, anaphylactoid reaction secondary to acute HIT), the presence of invasive catheters and the integrity of the surrounding ...