Polycythaemia is an abnormally high level of red blood cells. It is defined as a venous haematocrit greater than 65 per cent and occurs in 0.4-4 per cent 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
- cerebral infarction that may affect long-term neurological outcome.
Causes of polycythaemia
Most cases of polycythaemia occur in normal healthy infants and may result from a variety of reasons.
Placental red cell transfusion
Placental red cell transfusion may be caused by:
- delayed cord clamping, which may increase blood volume and red cell mass by as much as 55 per cent
- twin-to-twin transfusion syndrome.
Placental insufficiency with increased fetal erythropoiesis secondary to intra-uterine hypoxia
Placental insufficiency may occur in association with:
- small for gestational age infants
- post-mature infants.
Other causes of polycythaemia include:
- maternal substance use such as smoking
- maternal diabetes
- large for gestational age infant
- chromosomal abnormality (such as Down syndrome).
Signs and symptoms
Many polycythaemic infants are asymptomatic.
When present, the signs and symptoms of polycythaemia are non-specific and include:
- feeding problems
- respiratory distress
Investigation for polycythaemia includes the following:
- The diagnosis of polycythaemia is made on central or peripheral venous blood with a haematocrit over 65 per cent.
- Because capillary blood haematocrit is not reliable, a peripheral venous haematocrit should be performed if the capillary haematocrit is above 65 per cent.
- The haematocrit peaks at two hours of age, then falls by six hours of age and thereafter.
Management issues to note:
- Universal screening of haematocrit for polycythaemia is not warranted.
- Many selectively test for polycythaemia in high-risk infants (such as IDM and placental insufficiency).
Treatment for polycythaemia involves the following:
- Use liberal fluid intake and/or partial exchange transfusion (PET) to reduce the venous haematocrit below 60 per cent.
- Asymptomatic polycythaemic infants should have their fluid intake liberalised.
- PET using normal saline as the replacement fluid is recommended in symptomatic infants with a haematocrit above 70 per cent.
- PET is best performed through peripheral arterial and venous lines.
Volume of exchange (ml) = blood volume* (observed - desired haematocrit) / observed haematocrit
*Blood volume is:
- 70-90 mL/kg for term infants
- 85-110 mL/kg for preterm infants.
Areas of uncertainty in clinical practice
Areas of uncertainty include the following:
- Treatment of polycythaemia with PET remains controversial. While 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 per cent in asymptomatic infants.
- Risk of necrotising enterocolitis is probably increased by PET, so a decision should be based on symptoms and the potential for more serious complications.
- Long-term outcome is more likely related to the underlying cause of polycythaemia.
- 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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First published: May 2015
Last web update: October 2018
Review by: December 2020
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