Читать книгу Neonatal Haematology - Barbara J. Bain, Irene Roberts - Страница 40

The site of sampling also influences blood count analyses in neonates. For example, in the first few hours of life the Hb of venous samples is lower than that of heel‐prick samples collected simultaneously,¹⁵⁵ sometimes by up to 20–40 g/l.³⁵ This difference is greater in preterm neonates and falls with increasing postnatal age, such that by the fifth day of life there is almost no difference in Hb between a well‐taken heel‐prick sample and a venous sample.¹⁵⁵ Similarly, the haematocrit and red blood cell count at birth are lower in venous blood compared with capillary blood samples collected simultaneously, while there is no difference in the other red cell indices by site of sampling.¹⁵⁵ Neonatal heel‐prick samples have also been shown to have white cell, neutrophil and lymphocyte counts about 20% higher than arterial or venous samples; counts are most likely to approximate to those of venous blood if there is a free flow of blood and if early drops, excluding the first, are used for the count.³⁵ In contrast, the platelet count and mean platelet volume (MPV) are lower in capillary samples than in venous samples.^155,156