Many algorithms for detection and treatment of hypoglycaemia make a big deal of whether the hypoglycaemia is symptomatic or not. Symptomatic hypoglycaemia is supposed to be more dangerous in the long term, and requires more aggressive treatment. But symptoms accredited to hypoglycaemia also occur in non-hypoglycaemic infants, and many infants with low blood sugars look and act just like their normoglycaemic peers.

So bravo to a group of German investigators who have tried to determine whether clinical signs really discriminate between babies with and without low blood sugars. (Hoermann H, et al. Reliability and Observer Dependence of Signs of Neonatal Hypoglycemia. J Pediatr. 2022)

They video monitored 145 term and late preterm babies, some considered to be at-risk of hypoglycaemia (SGA, LGA, diabetic mothers, late preterm, and respiratory distress), and others at standard risk. 430 videos were taken just before the blood sample, which was analyzed by a bedside “Stat-strip” glucose analyzer. This is, I think, the main limitation of the study, as such monitors are known to be inaccurate, they produce results which tend to be lower than reference methods, when in the hypoglycaemic range. But if we assume that the hypoglycaemic babies were truly hypoglycaemic, which would often be true, then clinical signs, as detected by the 8 nurses and 2 neonatologists who reviewed all the videos, are completely unreliable.

The sensitivity and specificity of any of the clinical signs were poor, with tachypnoea being the clinical sign which was most different between babies with blood sugars above and below 2.5 mM/L (45 mg/dl).

Apart from the very rare baby with blood sugar of zero who is convulsing, clinical signs are really not much use in detecting hypoglycaemia, and there really is no reliable evidence that an infant with a low blood sugar who has some of these clinical signs has any worse prognosis than a baby with a similar blood sugar who is not thought to be symptomatic.

I really question the division of hypoglycaemia into “symptomatic” and “asymptomatic”; as these authors note, there is no good previous data that shows reliably that symptoms of hypoglycaemia are reproducible or readily detected, and nor is there good data that babies with what are considered to be signs of their low blood sugar are worse off in the long term than those without such clinical signs.