Thrombocytopenia in the Intensive Care Unit

Warren Isakow

Thrombocytopenia is a very common occurrence in the intensive care unit (ICU), occurring in as many as 60% of patients. The normal platelet count ranges between 150,000 and 450,000/µL. In the ICU, it is important to recognize that the absolute platelet count is important, but trends in the platelet count, specifically a decline by more than one-half, may be evidence of a serious clinical problem such as heparin-induced thrombocytopenia (HIT), which requires urgent attention. A systematic approach to the diagnosis allows for the common causes to be detected early and enables rational use of platelet transfusions (Algorithm 62.1). Platelet survival in the circulation is approximately 7 to 10 days, and one-third of the platelets are sequestered in the spleen under normal circumstances.

Recognition of thrombocytopenia normally occurs after a complete blood count is drawn, but it is important to remember that mucocutaneous bleeding is a classic sign of thrombocytopenia. Bleeding from thrombocytopenia normally occurs only once the platelet count is <50,000/µL in postsurgical patients; spontaneous bleeding can occur with counts <5000/µL. The diagnostic approach starts with a thorough history and physical examination, followed by examination of the peripheral smear. A pathophysiologic approach to thrombocytopenia enables all common causes to be rapidly screened for and facilitates recognition of potential causes (Table 62.1). Careful attention should be paid to prescription and over-the-counter drugs (Table 62.2).

The common causes of thrombocytopenia in an ICU setting are as follows:

Drug-induced (heparin, H₂-receptor blockers, GP2b3a inhibitors, antibiotics, alcohol)
Sepsis
Massive bleeding
Thrombocytopenia with microangiopathic hemolytic anemia (thrombocytopenic thrombotic purpura [TTP], hemolytic uremic syndrome [HUS], disseminated intravascular coagulation [DIC]).

Clinical recognition of the cause is vital, as the therapies differ considerably depending on the etiology. For example, a patient with thrombocytopenia secondary to bleeding should be treated with platelets compared with a patient with TTP/HUS, in whom platelet transfusion is generally contraindicated. A few common conditions will be discussed, and readers are encouraged to refer to Suggested Reading for further details.

ALGORITHM 62.1 Diagnostic Algorithm for Thrombocytopenia

TABLE 62.1 Pathophysiologic Classification of Thrombocytopenia

Decreased production		Increased destruction		Increased sequestration
Aplastic anemia		Immunologic		Hypersplenism from any cause:
Hematologic malignancies			ITP		Cirrhosis
	Lymphoma		Heparin-induced (HIT)		Portal hypertension
	Leukemia		Drug-induced (see Table 62.2)		Congestive heart failure
	Myelodysplasia		HIV		Hematologic malignancies
Metastatic malignancy			Autoimmune disease		Lipid storage disorders
Nutritional (vitamin B₁₂ and folate)			Infectious
Drugs (see Table 62.2)		Posttransfusion purpura
Chemotherapy and radiation		Antiphospholipid antibody syndrome
Alcohol		Nonimmunologic
Viral infections			DIC
	HIV		HUS/TTP
	Mumps		HELLP syndrome
	Parvovirus		Preeclampsia/eclampsia
	Varicella		Malignant HTN
	Rubella		Sepsis
	Epstein-Barr		Cardiac valves (prosthetic endocarditis)
	Hepatitis C		Burns
			Massive bleeding
HIV, human immunodeficiency virus; ITP, immune thrombocytopenic purpura; HIT, heparin-induced thrombocytopenia; DIC, disseminated intravascular coagulation; HUS, hemolytic uremic syndrome; TTP, thrombotic thrombocytopenic purpura; HELLP, hemolysis, elevated liver enzyme levels and a low platelet count; HTN, hypertension.