Neonatal hypoglycemia

Reduced blood glucose concentration (hypoglycemia) is one of the most common metabolic problems during the neonatal period. It may cause acute non-specific symptoms that include altered level of consciousness, feeding difficulties, seizures and even coma. 

Irrespective of the presence or absence of acute symptoms, untreated neonatal hypoglycemia is associated with risk of long-term neurological deficit that can result in mental retardation, recurrent seizures and personality disorder. One of the most enduring controversies surrounding neonatal hypoglycemia is the precise blood glucose concentration that should be used to make the diagnosis. 

According to the author of a recently published review article addressing this controversy, there is current widespread acceptance that even in the absence of clinical signs, hypoglycemia should be diagnosed if blood glucose is <2.6 mmol/L (47 mg/dL). This cut-off is higher than those recommended in the past, which have ranged from as low as 1.1 mmol/L (20 mg/dL) to 2.5 mmol/L (45 mg/dL). 

After an introductory brief discussion of the physiological reasons for the predisposition to relatively low blood glucose concentration during the early neonatal period, the author describes four different approaches that have been used over the years by researchers to define neonatal hypoglycemia. 

Of the four he suggests that the most useful approach is one based on neurological and developmental outcomes. These studies aim to correlate blood glucose concentration during the neonatal period with long-term neurological outcome. 

Much of the article is devoted to a critical assessment of one highly influential study that adopted this favored research approach and was largely responsible for the currently recommended 2.6 mmol/L cut-off value for diagnosis of neonatal hypoglycemia. 

The author argues that the study had significant shortcomings and that the evidence base derived from this and more recent research is not sufficiently robust to support continued use of a single 2.6 mmol/L cut-off value. Instead he recommends, in line with other authorities, the use of a more pragmatic “operational threshold” approach to the diagnosis of neonatal hypoglycemia. 

This approach states that clinicians should only consider treatment of neonatal hypoglycemia in the event of any of the following three scenarios:

• A single blood glucose measurement of <1.0 mmol/L (18 mg/dL)
• Blood glucose <2.0 mmol/L (36 mg/dL) that remains below the same value at the next measurement (i.e. is not rising)
• A single measurement of <2.5 mmol/L in a newborn with abnormal clinical signs

With this approach, diagnosis of neonatal hypoglycemia does not depend solely on blood glucose (unless it is particularly low) but also on the clinical condition of the infant.

Irrespective of the precise blood glucose concentration used to diagnose neonatal hypoglycemia, the author makes clear that there is universal agreement that the use of bedside reagent test strips to monitor blood glucose in the neonate is to be discouraged as they have been shown to be unreliable at low glucose concentrations.