++
The hematocrit (Hct) is 68% in a newborn. Polycythemia is defined as a venous hematocrit above 65% or a hemoglobin >22 g/dL. Polycythemia occurs in 2–4% of newborns and is rare in premature infants <34 weeks' gestation. The current definition and management of neonatal polycythemia is empirical and not evidence based. Polycythemia may result in an increase in blood viscosity, which causes a reduction in blood flow, acidosis, hypoglycemia, tissue hypoxia, and an increase in microthrombi formation. Hyperviscosity is defined as a viscosity value >14 centipoise (shear rate of 11.5 seconds) and is also defined as 2 standard deviations greater than the norm. Polycythemia hyperviscosity syndrome (PHS) is the symptom complex that involves polycythemia, hyperviscosity, and the symptoms that accompany it. Forty seven percent of polycythemic infants have hyperviscosity. Twenty-four percent of infants with hyperviscosity have polycythemia.
++
II. IMMEDIATE QUESTIONS
++
What is the central hematocrit (Hct)? In blood obtained by heelstick, the Hct may be falsely elevated by up to 5–20%. Treatment should never be initiated based on heelstick Hct values alone; a central (peripheral venous phlebotomy) Hct is needed. If the sample is from the umbilical vein or radial artery, the upper limit of normal is 63%. The hematocrit in a newborn peaks at 2 hours of age and then decreases to a baseline by 24 hours of age. A micro-centrifuge hematocrit can be 2% higher than hematocrit by a hematology analyzer.
Does the infant have symptoms of polycythemia? Many infants with polycythemia are asymptomatic. Symptoms of hypoperfusion correlate more with viscosity than the hematocrit. One study found that feeding problems and lethargy were the most common symptoms. There are many signs of polycythemia, most of them nonspecific, which can include the following:
Central nervous system. Lethargy, hypotonia, irritability, jitteriness, weak sucking reflex, vomiting, seizures, tremulousness, apnea, sleepiness, exaggerated startle, tremors, and cerebrovascular accidents.
Cardiovascular. Heart murmurs, congestive heart failure, cyanosis, plethora, tachycardia, cardiomegaly, and prominent vascular markings on chest radiograph.
Respiratory. Respiratory distress, tachypnea, and cyanosis.
Gastrointestinal. Poor feeding, poor sucking, vomiting, and necrotizing enterocolitis (NEC).
Renal. Proteinuria, oliguria, hematuria, renal vein thrombosis and decreased glomerular filtration rates, and transient hypertension.
Hematologic. Thrombocytopenia, hepatosplenomegaly, thrombosis, disseminated intravascular coagulation (rare), and elevated reticulocyte count.
Metabolic. Hypoglycemia (most common; 12–40%), hypocalcemia (1–11%), and increased jaundice (hyperbilirubinemia).
Skin. Plethora or ruddiness.
Genitourinary (GU). Testicular infarcts or priapism (majority are idiopathic).
Is the mother diabetic? Poor maternal control of diabetes during pregnancy leads to chronic fetal hypoxia, which may result in increased neonatal erythropoiesis. Infants of diabetic mothers have a 25 to >40% incidence of polycythemia. Infants of mothers with gestational diabetes also have an increased incidence (30%) of polycythemia.
What is the infant's age? The Hct normally rises after birth and reaches a peak at 2 hours of age, and then slowly decreases and stabilizes by 12 to 24 hours of age.
Is the infant dehydrated? Dehydration may cause hemoconcentration, resulting in a high Hct. It usually occurs in infants >48 hours old.
Does the mother live at a high altitude? Infants born to mothers at high altitudes have a higher incidence of polycythemia.
Is the infant at high risk for polycythemia? Infants that are small for gestational ...