Thrombocytopenia in the Critical Care Patient
Terry B. Gernsheimer
I. GENERAL PRINCIPLES
A. Definition.
1. Less than 150,000/µL, generally not clinically significant until <100,000/µL.
2. Relative—an acute drop from a higher platelet count may be pathologic.
B. Pathophysiology.
1. Decreased production.
2. Increased destruction, consumption.
3. Increased sequestration in enlarged spleen.
4. Dilutional—effect of massive transfusion and fluid resuscitation.
5. States with multiple causes of thrombocytopenia.
a. Cirrhosis with portal hypertension.
b. Hepatitis.
c. Human immunodeficiency virus (HIV).
d. Other viral illnesses.
e. Patients with multiple medical problems on multiple drugs.
C. Diagnosis.
1. Complete blood count with peripheral smear examination.
a. Rule out pseudothrombocytopenia due to platelet clumping.
b. Review for erythrocyte abnormalities: schistocytes, teardrops, nucleated red blood cells.
c. Review for white blood cell abnormalities: immature or dysplastic forms.
2. Coagulation testing.
a. Identify associated coagulation abnormalities.
3. Additional blood tests.
a. Viral titers and antibody (e.g., HIV, hepatitis C [HCV] infection).
b. Autoimmune disorders—antibody testing.
c. Other—see specific disorders.
4. Radiologic.
a. Abdominal ultrasound—evaluation of spleen size.
b. CT scanning—evaluation for lymphoproliferative disease.
TABLE 89-1 Target Platelet Count Values in Selected Clinical Scenariosa | ||||||||||||||||||
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5. Bone marrow examination indications.
a. Unclear pathophysiology.
b. Multiple cytopenias.
c. Suspected infiltrative process.
D. Therapy (Table 89-1).
1. Indications for platelet transfusion.
a. Bleeding or necessary invasive procedures.
b. Prophylactic—very severe (<10,000/µL) thrombocytopenia or <20,000 when fever or mucositis are present.
c. Other blood components as indicated to correct coagulation abnormalities or severe anemia.
d. Relative contraindications to platelet transfusion.
i. Thrombotic thrombocytopenic purpura (TTP) unless bleeding is present—worsened thrombotic tendency reported.
ii. Immune thrombocytopenia unless bleeding present—poor or short-lived response.
iii. Heparin-induced thrombocytopenia (HIT) without bleeding— unknown.
2. Nonspecific therapy for bleeding.
a. Antifibrinolytic agents—Epsilon-aminocaproic acid, tranexamic acid.
b. Recombinant factor VIIa (Novo Seven)—unproven and controversial. May be indicated in acute intracranial, other life-threatening bleeding in patients without response to platelet transfusion.
3. Secondary thrombocytopenias—direct therapy at underlying cause(s).
4. Primary thrombocytopenia—depends on specific disorder.
II. DECREASED PLATELET PRODUCTION
A. Isolated thrombocytopenia.
1. Drugs, ETOH, viral (e.g., HIV, HCV).
2. Decreased thrombopoietin—liver disease.
3. Amegakaryocytic thrombocytopenia.
B. Multiple cytopenias.
1. Marrow toxins.
a. Drugs, alcohol, radiation.
2. Nutritional—for example, B12 and/or folate deficiency.
3. Metabolic—for example, thyroid disorders.
4. Primary marrow disorders.
5. Hematopoietic stem cell disorders.
a. Marrow infiltration.
6. Hemophagocytic syndrome.
C. Diagnosis.
1. Peripheral blood smear.
a. Bizarre forms—for example, abnormal granulation suggests myelodysplasia.
b. Red blood cell abnormalities.
i. Teardrops, nucleated red blood cells—suggest marrow infiltrative diseases.
ii. Macrocytosis—B12 or folate deficiency, myelodysplasia.
c. White blood cell abnormalities.
i. Immature forms—suggest leukemia.
ii. Multilobed neutrophils, bizarre forms—B12 or folate deficiency, myelodysplasia.
D. Therapy.
1. Direct at underlying or associated disorder.
III. INCREASED SPLENIC SEQUESTRATION
A. Etiology.
1. Portal hypertension.
2. Myeloproliferative disease.
3. Lymphoma.
4. Storage and infiltrative diseases of the spleen.
5. Chronic hemolysis.
6. Granulomatoses—for example, tuberculosis, sarcoidosis.
B. Diagnosis.
1. Imaging—abdominal ultrasound, CT.
2. Biopsy of apparently pathologic tissue, bone marrow.
C. Treatment.
1. Direct at underlying cause.
IV. DISORDERS OF INCREASED PLATELET DESTRUCTION
A. Characterized by shortened platelet life span (normal 7 to 10 days).
B. Nonimmune—isolated or combined platelet consumption.
C. Autoimmune.
D. Alloimmune.
V. AUTOIMMUNE THROMBOCYTOPENIAS
A. Etiology.
1. Primary—immune thrombocytopenic purpura (ITP).
2. Secondary.
a. Associated with other autoimmune disease, for example, systemic lupus.
b. Associated with malignancy (e.g., lymphoproliferative disease).
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