Chapter 32

### INTRODUCTION

Thrombocytopenia is a well-recognized phenomenon in the neonatal intensive care unit (NICU); it can lead to morbidity and mortality from severe and life-threatening bleeding. The epidemiology, pathophysiology, causes, management, and outcome of neonatal thrombo­cytopenia are reviewed in this chapter.

Thrombocytopenia is traditionally defined as a platelet count below 150,000/μL. This definition is based on several population studies, which have demonstrated that in mothers with normal platelet counts, over 98% of healthy term neonates have platelet counts greater than 150,000/μL at birth.1, 2, and 3 Thrombocytopenia is rare in healthy newborns; however, it affects up to one-third of patients in the NICU.4, 5 The increased incidence of thrombocytopenia in NICU patients is reflective of the inverse relationship of thrombocytopenia risk to birth weight and gestational age.4, 6 Christensen et al reported that up to 70% of infants with birth weight less than 1000 g are thrombocytopenic.6 Preterm infants, particularly those at less than 24 weeks’ gestation, have platelet counts as low as 100,000/μL in the first few days of life.4, 7

Severe thrombocytopenia is defined as a platelet count of less than 50,000/μL. Severe thrombocytopenia occurs in less than 1% of healthy newborns2, 3, but affects 5%–10% of hospitalized neonates.4, 8, 9

### CAUSES OF NEONATAL THROMBOCYTOPENIA

The causes of neonatal thrombocytopenia can be classified into 2 major pathophysiologic categories: increased destruction (including consumption) and decreased production. In some neonates, especially sick preterm infants, both processes can occur concomitantly. The time of thrombocytopenia onset has often been used to help with diagnosis. Early-onset thrombocytopenia occurs within 72 hours of birth, while late-onset thrombocytopenia occurs after 72 hours of life (Table 32-1). Diagnostic algorithms and general management of neonatal thrombocytopenia are highlighted in Chapter 92.

Table 32-1Classification of Early-Onset (72 Hours Postbirth) Thrombocytopeniasa,b

The diagnoses of thrombocytopenia based on underlying pathophysiologic classifications are summarized in Table ...

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