Table 1

Early investigations to assess neonatal encephalopathy

First line investigationsComment
Full blood countMay suggest infection, haemorrhage, thrombocytopenia.
ClottingClotting disorders may be seen in HIE and sepsis, but should also lead the clinician to think about anaemia secondary to inherited coagulation disorders and intracranial haemorrhage.
Direct Coombs testEvidence of haemolysis.
Liver function testMay be abnormal in HIE but is usually transient unless a severe insult to the liver has occurred. Abnormal liver function tests can be a feature of bilirubin encephalopathy, metabolic conditions, congenital infections, and acute sepsis with bacteria and viruses, including herpes simplex virus.
Urea and electrolytesMay be impaired if the kidneys have had an ischaemic insult but usually improves, unless severe ischaemic injury has occurred. May also be impaired in congenital abnormalities of the kidneys, metabolic conditions.
Whole blood glucose (rather than serum glucose as the latter is around 15% higher than whole blood)Hypoglycaemia may be seen following HIE, but is usually correctable with appropriate treatment. Persistently low glucose requires further evaluation.
Blood lactateLactate is often measured on the blood gas, and may increase rapidly to high levels following HIE, but usually falls within days and returns to normal. A persistently high lactate should trigger further investigations.
NeurophysiologyAmplitude integrated EEG (aEEG) using a cerebral function monitor and/or serial standard EEGs to identify seizures and monitor recovery of encephalopathy. Will also help diagnose neonatal epilepsy syndromes.
Second line investigations to consider ordering which are available quickly (if concerned this is not typical HIE)
Urinary ketonesUrinary ketones, when present, in a neonate indicate the use of intermediary pathways of metabolism and are almost pathognomonic of the presence of a metabolic disorder.
AmmoniaIn very sick neonates, ammonia, up to about 110 μmol/L may be present. Very high levels (>200 μmol/L) usually indicate a metabolic cause, for example, urea cycle defect and warrants further investigations.
  • HIE, hypoxic-ischaemic encephalopathy.