What is the normal range of blood glucose concentrations in healthy term newborns?
- Report By Richard Nicholl, Consultant Neonatologist, Northwick Park Hospital, Northwest London NHS Hospitals Trust, UK
You are the attending neonatal consultant. It is 6 pm on a Friday after a busy week on the unit. A rather flustered midwife appears from the postnatal ward with a baby and two anxious parents. The baby is full term and appropriately grown, following a normal vaginal delivery and just 8 hours old. Mum has been attempting to breast feed but the baby is reported to have been “not feeding well” and “jittery”. There are no prenatal risk factors for sepsis. Your examination of the baby is normal—he is now not “jittery”.
A capillary heel prick blood test (Medisense) done on the postnatal ward has given a blood glucose reading of 2.6 mmol.
Because this result is perceived to be abnormal (low), one of the neonatal trainees has suggested to the parents that he may need admission to the neonatal unit. As she has had three previous babies, the mother was hoping for an early (six hour) discharge from hospital.
The midwife asks you to “sort out the situation”.
Some hours later, the laboratory plasma glucose result (taken at the same time as the Medisense capillary sample) is available. This result is 3.4 mmol/l.
The mother agreed to stay overnight with the baby on the postnatal ward, received breast feeding support, and was discharged home next morning. No further blood samples were taken. A phone call to the mother on day 3 confirmed that the baby remained well and fully breast fed.
Structured clinical question
In otherwise healthy newborn babies, what is the normal range of blood glucose, in the first days of life?
Search strategy and outcome
[newborn] AND [blood glucose OR hypoglycaemia] AND [Exp cohort studies]
Cochrane Library: no relevant studies found.
Primary sources (Medline): 3 observational studies.
See table 3.
CLINICAL BOTTOM LINE
The normal range of blood glucose is around 1.5–6 mmol/l in the first days of life, depending on the age of the baby, type of feed, assay method used, and possibly the mode of delivery.
Up to 14% of healthy term babies may have blood glucose less than 2.6 mmol/l in the first three days of life. Lowest concentrations are more likely on day 1.
There is no reason to routinely measure blood glucose in appropriately grown term babies who are otherwise well. “Jitteriness” is a mostly benign finding.
Feeding difficulty should be overcome with education, promotion, and support for breast feeding.
There was remarkable agreement between the results of these three studies in spite of different populations (UK, Denmark, and India) and different methods of assay (whole blood glucose: microenzymatic and glucose dehydrogenase photometric methods; plasma glucose: glucose oxidase method).
Breast fed babies have statistically significantly lower blood glucose concentrations (mean 3.6 mmol/l; range 1.5–5.3) in the first week of life, compared to formula fed babies (mean 4.0 mmol/l; range 2.5–6.2).
Breast fed full term babies with low blood glucose concentrations produce ketones and other fuels as an adaptive mechanism.
Jitteriness is an extremely common and usually benign finding in otherwise well term newborns.1 In a study of 102 full term babies with “jitteriness”,2 sucking on the examiner's hand stopped the tremor in over 80%. Of the 18 babies whose tremor continued, only five had hypoglycaemia and 13 had hypocalcaemia
In our case, the difference between the Medisense heel prick (2.6 mmol/l) and the laboratory plasma glucose of 3.4 mmol/l, highlights the poor predictive value of reagent strips to detect true hypoglycaemia (PPV 0.18 for blood glucose of <2.0 mmol/l). Use of reagent strips will on average wrongly diagnose hypoglycaemia in one out of four babies who are in fact normoglycaemic.3
If a baby appears well but “jittery”, he or she should be examined carefully and have a suckling stimulation test. If he or she fails this test, blood assay of calcium and glucose should be done. Blood glucose of less than 1.5 mmol/l should prompt further investigation in any baby (well or otherwise).