Decoding the full blood count (haematocrit)

Part 2 of “Decoding the full blood count” with thanks to Dr Alexandra Briscoe, paediatric registrar at Whipps Cross University Hospital, and Professor Irene Roberts, professor of paediatric haematology at Oxford.


Haematocrit/packed cell volume

Haematocrit/ packed cell volume- the proportion of blood that is made up of cells (not plasma); it is measured as a percentage or fraction.

Low haematocrit is seen in anaemia, though it will not tell you the direct cause for the anaemia.

Raised haematocrit is seen in polycythaemia, in the newborn infant this is termed Neonatal Polycythaemia.

Defined as a venous haematocrit > 65%, occurring in 0.4-5% of healthy newborns. Symptoms are believed to be due to hyperviscosity. On examination children appear plethoric, and may have multi-systemic symptoms. These include- CNS features of irritability, cerebrovascular accidents and seizures. Apnoea and respiratory distress occur as a result of decreased pulmonary blood flow. In addition infants may demonstrate poor feeding, and may in rare cases develop necrotising enterocolitis (NEC.) Renal effects include renal vein thrombosis, oliguria, proteinuria and haematuria.  Hypoglycaemia and thrombocytopenia (Vlug, 2013) are also seen commonly.

The development of polycythaemia occurs secondary to increased erythropoiesis as a consequence of chronic fetal hypoxia. IUGR and placental insufficiency- due to post-dates pregnancies, pre-eclampsia and maternal smoking, increase the incidence of polycythaemia. Infants of diabetic mothers, those with Beckwith –Weidemann, and congenital thyrotoxicosis are also at increased risk.

There has been much debate as to whether delayed cord clamping increases the incidence of polycythaemia. Current NICE guidelines recommend cord clamping between 1-5 minutes after delivery, provided there is no concern regarding the infant’s heart rate or need for resuscitation. In a Cochrane review of cord clamping practices and neonatal outcomes in 2013 McDonald et al found that delayed cord clamping was associated with increased risk of jaundice requiring phototherapy, however beneficial outcome in terms of iron stores- with a 50% reduction in iron deficiency at 3-6 months. They reported no difference in incidence of polycythaemia in 5 trials measuring this outcome.

Current management of symptomatic polycythaemia is a partial exchange transfusion.


Vlug RD, Lopriore E, Janssen M, et al. Thrombocytopenia in neonates with polycythemia: incidence, risk factors and clinical outcome. Expert Rev Hematol. 2015 Feb. 8 (1):123-9. [Medline].

ID: CD004074 McDonald, Susan J, Middleton, Philippa, Dowswell, Therese Morris, Peter S

Effect of timing of umbilical cord clamping of term infants on maternal and neonatal outcomes

Cochrane Database of Systematic Reviews 2013

DOI: 10.1002/14651858.CD004074.pub3


What are normal haematocrit levels?

(taken from

The normal ranges for haematocrit  depend on the age and, after adolescence, the sex of the individual. The normal ranges are:

  • Newborns: 55% to 68%
  • One (1) week of age: 47% to 65%
  • One (1) month of age: 37% to 49%
  • Three (3) months of age: 30% to 36%
  • One (1) year of age: 29% to 41%
  • Ten (10) years of age: 36% to 40%
  • Adult males: 42% to 54%
  • Adult women: 38% to 46%

These values may vary slightly among different laboratories.

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