Neonatal bilirubin production, reflected by carboxyhaemoglobin concentrations, in Down's syndrome
Michael Kaplana b, Hendrik J Vreman, Cathy Hammermana b, David K Stevensonc
a Department of
Neonatology, Correspondence to: Dr
Michael Kaplan
Department of Neonatology
Shaare Zedek
Medical Center
Box 3235 Jerusalem 91031 Israel.
Email: kaplan{at}cc.huji.ac.il
Accepted 2 December
1998
AIM
To determine
whether increased bilirubin production, reflected by blood
carboxyhaemoglobin (COHb) values, is responsible for hyperbilirubinaemia in cases of Down's syndrome with no obvious cause
for excessive jaundice.
METHODSBlood was
sampled on the third day of life for COHb, total haemoglobin (tHb), and
serum total bilirubin, from 19 consecutively born neonates with Down's
syndrome (a subset of 34 term babies), who had developed
hyperbilirubinaemia (serum bilirubin 
256 µmol), and from 32 term
controls. COHb, measured by gas chromatography, was corrected for
inspired CO (COHbc) and expressed as a percentage of tHb.
RESULTSSignificantly
more of the Down's syndrome subset developed hyperbilirubinaemia than
the controls (10/19 (52%) vs 7/32 (22%), relative risk 2.4, 95% confidence intervals (CI) 1.10 to 5.26). Third
day serum bilirubin values (mean (SD)) were higher in the Down's
syndrome neonates than in controls (214 +- 63 µmol/l
vs 172 +-
54 µmol/l, respectively, p=0.015). Mean (SD) COHbc values were
significantly higher in the Down's syndrome neonates than in controls
(0.92 +- 0.24%
vs 0.63 +-
0.17%; p<0.0001). However, Down's syndrome neonates who became
hyperbilirubinaemic had similar COHbc values to those who did not (0.87 +- 0.26% and 0.95 +- 0.23%, respectively). These values
contrast with those of the controls, in whom a significant increase in
COHbc was associated with hyperbilirubinaemia (0.74 +- 0.15% vs
0.60 +- 0.16%, respectively;
p<0.05). tHb values were similar in both groups.
CONCLUSIONSDown's
syndrome neonates had a greater risk of hyperbilirubinaemia, and higher
COHbc values, than controls. However, excessive bilirubin production
could not be exclusively responsible for the hyperbilirubinaemia. By
inference, decreased bilirubin elimination probably plays a greater
part in its pathogenesis than in controls. Down's syndrome neonates
may have abnormal erythropoiesis, leading to increased haem turnover.
Keywords:
Down's syndrome;
carboxyhaemoglobin;
carbon
monoxide;
jaundice;
bilirubin production;
haemolysis
© 1999 by Archives of Disease in Childhood
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