Thrombocytopenia

Mark D. Darrow

A low platelet count is usually brought to the attention of the practitioner as the result of an automated complete blood count in an asymptomatic patient (1).

I. Approach. In working through the differential diagnosis of thrombocytopenia, it is helpful to categorize it by cause and severity of clinical presentation.

 A. Causes. Platelet counts fall secondary to a decrease in production, increased consumption, destruction, sequestration or dilution, and from physiologic causes. Errors in measurement and specimen collection also contribute to the causes of thrombocytopenia (Table 16.3).

 B. Common concerns. When does bleeding become a problem? Susceptibility to bleeding is specific to the individual; however, bleeding is rare above a platelet count of 100,000/mm³ (100 × 10⁹/L). With platelet counts between 20,000 mm³ to 50,000/mm³ (20 − 50 × 10⁹/L), bleeding from trauma or surgery can occur. At this level, bleeding in the form of petechiae can occur in the mouth, on legs, along brassiere straps and undergarments, and in the genital area. Spontaneous bleeding occurs with counts less than 20,000/mm³ (20 × 10⁹/L) from or within many body organs. Life-threatening hemorrhage from the gastrointestinal tract or the central nervous system usually occurs at extremely low platelet counts, 5000/mm³ (5 × 10⁹/L) or less (2) (Chapter 9.7).

 
II. History

A. Pertinent recent and past history. Has there been any indication of a low platelet count? Easy bruisability, nose bleeds, petechiae, for example. Does the patient have any acute or chronic medical conditions such as pregnancy, infections, connective tissue diseases, alcohol abuse, medication use (quinidine, heparin), or liver disease?

B. Family history. Are there any relatives with a history suggestive of congenital thrombocytopenic or platelet function disorders?

 C. Surgical history. Has the patient had a cardiac valve or other device implanted in the past? Does the patient have an implanted artificial joint that can serve as a source of infection? Is there is history of a splenectomy?

 D. Medications. Heparin, quinidine, and gold therapy are well known to be associated with drug-related, immune-mediated thrombocytopenia. Recreational use of cocaine can also cause this condition. Many other drugs can lower platelet counts through various other mechanisms (antiinflammatory agents, β-lactamase–resistant antibiotics) (2,3).

 
III. Physical examination. The physical examination should be directed at finding evidence of bruising or bleeding. Look for petechiae on the skin or mucosa, particularly in dependent areas and in areas of pressure, as well as in the mouth and perianal and vulvar areas. Stool guaiac evaluations are also important (2–4) (Chapters 9.11 and 15.3).

Evidence of lymphadenopathy, hepatosplenomegaly, jaundice, fever, and neurologic abnormalities suggests the presence of systemic illnesses that can be associated with and be the cause of the patient’s thrombocytopenia (4,5).

IV. Testing

 A. Blood tests. The first step in the laboratory evaluation is to repeat the platelet count. Clumping or laboratory error may have occurred during the first reading. A complete blood count and an evaluation of the peripheral blood smear help narrow the differential diagnosis based on the presence and number of certain cell types and forms. The remainder of the laboratory evaluation—liver function tests, renal function tests, vitamin B₁₂ and folate levels, and antibody screening—should be guided by historical and physical findings. A bone marrow evaluation may be appropriate if the peripheral smear suggests bone marrow-based pathology (hypoplasia, malignancy, and fibrosis) (2,4,5).

 B. Diagnostic imaging. Imaging studies (e.g., an ultrasound of the abdomen for evaluation of liver and spleen size) are appropriate in some situations where the physical examination of these organs was not adequate. Computerized tomographic (CT) images of the brain should be considered when neurologic findings exist. CT images of the chest, abdomen, and pelvis will help evaluate adenopathy if present peripherally and its extent in the thoracic and abdominal cavities (4,5).

 
V. Diagnostic assessment. To determine the cause of thrombocytopenia, give equal consideration to the history, physical examination, and laboratory findings. Some causes may be obvious; others may consume time and require some further evaluation. For example, the thrombocytopenic patient recently started on quinidine for a cardiac dysrhythmia should have this medication discontinued and the platelet count followed for return to the normal range. A second patient with multiple sexual partners, a history of systemic lupus erythematosus, pain medication abuse, and newly diagnosed adenopathy may require a more extensive evaluation.

Whatever the cause, urgency in the workup of the thrombocytopenia is often driven by the clinical presentation and any clinically significant bleeding that may be present.

References

1. George JN, el-Haroke MA, Raskob GE. Chronic idiopathic thrombocytopenia purpura. N Engl J Med 1994;331:1207–1211.

2. Goldstein KH, Abramson N. Efficient diagnosis of thrombocytopenia. Am Fam Physician 1996;53(3):915–920.

3. Rithell T. Wintrobe’s clinical hematology, 9th ed. Philadelphia: Lea and Febiger, 1993:1325–1373.

4. Schrier SL, Leung LLK. Disorders of hematosis and coagulation. In: Dale DC, Federman DD. Scientific American Medicine. Scientific American, Inc., 1997:11–39.

5. Shuman M. Hemorrhagic disorders: abnormalities of platelet and vascular function. In: Wyngaarden JB, Smith LH, Bennett JC, eds. Cecil textbook of medicine, 19th ed. Philadelphia: WB Saunders, 1992;987–999.

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Book Source Details

• Book Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter
• Author(s): Robert B. Taylor (editor)
• Year of Publication: 2000
• Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2000 Lippincott Williams & Wilkins.

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More About This Book: Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter Authors: Robert B. Taylor (editor) Publisher: Lippincott Williams & Wilkins Copyright: 2000 ISBN: 0-78172-094-X

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