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Treatment
The GDG therefore considered that there was a compelling need to provide specific guidance to
clinicians regarding thresholds for treatment. When determining the thresholds, the GDG
considered that the primary aim was to choose a threshold with a wide margin of safety, with
the threshold for phototherapy well below that for exchange transfusion. The rationale for this
was the difference in the safety profile between the two therapies. However, the choice of
threshold should not be so low that phototherapy would be used unnecessarily. In choosing the
threshold levels, the GDG considered that account should be taken of current common practice
while eliminating more extreme threshold strategies.
Phototherapy thresholds for infants of 38 weeks or more gestation
For babies of 38 or more weeks of gestation, the GDG agreed through an informal consensus
process that a reasonable threshold for initiation of phototherapy was 350 micromol/litre in
infants aged 96 hours or more. The GDG believed that this was consistent with current views on
the low risk associated with moderate hyperbilirubinaemia in term babies. The GDG discussed
a recent publication that provided data on current practice regarding thresholds for therapy in a
1
large number of units in the UK. That publication did not draw conclusions regarding ‘best
practice’ but did inform the group about the range of policies being used. The GDG noted that
their chosen phototherapy threshold was closely comparable with the most commonly reported
1
threshold (340 micromol/litre) currently used by units in the UK. It was also comparable with
the threshold proposed by the American Academy of Pediatrics. 123 There was evidence that the
publication of the AAP recommendation in 1994 had not been associated with a significant
change in the reporting of kernicterus cases in the USA. 124
For the period from birth to 96 hours, again based on informal consensus, the GDG agreed on a
series of bilirubin levels with 6-hourly stepwise increases at which phototherapy is
recommended until the 96-hour threshold of 350 micromol/litre is reached. These
recommended levels are presented in table form (see the threshold table in Section 1.3).
Phototherapy thresholds for infants less than 38 weeks of gestation
With regard to preterm babies, one longstanding and common approach has been to determine
the threshold for phototherapy using the simple formula
bilirubin in micromol/litre = (gestational age × 10) − 100
This formula has been proposed for use in paediatric textbooks for many years. Based on
informal consensus, the GDG agreed that this formula should be used for babies aged 72 hours
or older. The GDG noted that use of this simple formula produced a threshold for phototherapy
that was either within or close to the middle quartiles for thresholds reported to be in current
use by neonatal units in the UK. They were therefore comparable with ‘average practice’ and
would avoid some of the more extreme values being employed in some units. The widespread
use of this formula is not likely to change the number of preterm babies treated with
phototherapy in most neonatal units.
For all babies aged less than 72 hours, based on informal consensus, the GDG agreed that the
threshold should be lower because of the evidence that shows that bilirubin levels are rising for
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the first few days of life.
It was agreed for babies less than 38 weeks of gestation the threshold for phototherapy was best
presented using a series of graphs (see treatment threshold graphs) of total bilirubin versus age in
hours, with a separate graph for each gestational age (from 23 weeks to 37 weeks of gestation).
The graphs were constructed using the formula for infants of 72 hours of age and older. The
threshold levels during the first 72 hours were determined by drawing a straight line from a
level of 40 micromol/litre (the upper limit of normal for the umbilical cord blood bilirubin) at
birth to the formula-based level at 72 hours. The GDG were aware that Excel spreadsheets
originally devised by Dr Giles Kendall and Professor T J Cole at University College London
could potentially be used to display the threshold levels in graphic form. The GDG are grateful
to them for their kind permission to adapt these spreadsheets.
Exchange transfusion thresholds for babies of 38 weeks or more gestation
Similar considerations were applied to the choice of levels for exchange transfusion. The
process was one of informal consensus by the GDG.
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