Polycythaemia
Introduction
Polycythaemia is defined as a venous haematocrit greater than 65% and occurs in 0.4 - 4% of newborn infants. This may result in increased blood viscosity and therefore reduced blood flow, impaired tissue oxygenation and a tendency to microthrombus formation exacerbated by hypoxia, acidosis and/or poor perfusion. Thrombosis may result in renal venous thrombosis, adrenal insufficiency, necrotising enterocolitis and cerebral infarction that may affect long-term neurological outcome.
Causes
Although most cases of polycythaemia occur in normal healthy infants, polycythaemia may result from
- placental red cell transfusion (delayed cord clamping, twin to twin transfusion syndrome)
- placental insufficiency with increased fetal erythropoiesis secondary to intra-uterine hypoxia
- small for gestational age infants
- pre-eclampsia
- postmature infants
- other
- maternal diabetes
- large for gestational age infant
- chromosomal (e.g. Down Syndrome)
Many polycythaemic infants are asymptomatic. When present, the signs and symptoms of polycythaemia are non-specific and include
- feeding problems
- plethora
- lethargy
- cyanosis
- respiratory distress
- jitteriness
- hypotonia
- hypoglycaemia jaundice
- hypocalcaemia
- thrombocytopenia
Investigation
The diagnosis of polycythaemia is made on central or peripheral venous blood with a haematocrit over 65%. Because capillary blood haematocrit is not reliable, a peripheral venous haematocrit should be performed if the capillary haematocrit is above 65%. The haematocrit peaks at 2 hours of age, then falls by 6 hours of age and thereafter.
Management
- universal screening of haematocrit for polycythaemia is not warranted. Many selectively test for polycythaemia in high-risk infants (e.g. IDM, placental insufficiency)
- treatment of polycythaemia is with liberal fluid intake and/or partial exchange transfusion (PET) to reduce the venous haematocrit below 60%. Asymptomatic polycythaemic infants should have their fluid intake liberalized. PET using Normal Saline as the replacement fluid is recommended in symptomatic infants with a haematocrit above 65%
Volume of exchange (ml) = blood volume*(observed - desired haematocrit)/ observed haematocrit
*Term blood volume is 85 ml/kg
This is best performed through peripheral arterial and venous lines.
Areas of Uncertainty in Clinical Practice
Treatment of polycythaemia with PET is controversial. Whilst it may improve symptoms, there is no evidence that it improves long-term outcome in either asymptomatic or symptomatic polycythaemic infants. Partial exchange transfusion may be associated with earlier improvement of symptoms. In spite of inconclusive evidence, some still advocate PET when the venous haematocrit is above 70% in asymptomatic infants. Necrotising enterocolitis is probably increased by partial exchange transfusion. Long term outcome is more likely related to the underlying cause of polycythemia.
References
American Academy of Pediatrics Committee on Fetus and Newborn. Routine Evaluation of blood pressure, hematocrit and glucose in newborns. Pediatrics 1993;92:474-6
Dmpsey EM and Barrington K. Shortand long term outcomes follwoing partial exchange transfusion in the polycythemic newborn: a systematic review. Arch. Dis.Child. Fetal Neonatal Ed. 2006;91;2-6
Werner EJ. Neonatal polycythemia and hyperviscosity. Clinics in Perinatology 1995;22:693-710.
Wiswell TE, Cornish JD, Northam RS. Neonatal polycythemia: frequency of clinical manifestations and other associated findings. Pediatrics 1986;78:26-30
Wong W, Fok T, Lee CH et al. Randomised controlled trial: comparison of colloid or crystalloid for partial exchange transfusion for treatment of neonatal polycythemia. Arch Dis Child 1997;77:F115-8
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