Table 5

Investigation of non-traumatic coma

Investigations Indication/clinical clues Possible abnormality Further investigation if abnormal Possible diagnoses Action
DextrostixAllLowBlood glucoseHypoglycaemia secondary to:Intravenous dextrose
Blood glucoseLiver function tests• FastingFluids/insulin
Blood ammonia• Severe illness
Blood lactate• Reye's syndrome
Blood and urine amino acids• Organic aciduria
Urine organic acids• Fatty acid oxidation defect
• Haemorrhagic shock and encephalopathy
Previous polydipsia/polyuriaHighDiabetic ketoacidosis
Blood sodiumAllLowUrinary sodiumHypo/hypernatraemia +/− dehydrationAppropriate fluids
Blood ureaAllHighBlood creatinineDehydrationRehydrate
Blood filmHaemolytic-uraemic syndromeDialysis, plasmapheresis
Aspartate transaminaseAllHighBlood ammoniaReye's syndrome
Blood ammoniaAll (unless cause known)HighBlood orotic acidUrea cycle defectSodium benzoate
Urine organic acidsOrganic acidaemia
Full blood count and filmAllLow HbHb electrophoresisAnaemiaTransfusion
High WBCInfection3rd generation cephalosporin
Low plateletsDIC, infection
Sickle cellsSickle cell disease
Burr cellsHaemolytic-uraemic syndromeDialysis, plasmapheresis
Residence in endemic areaParasites on thick/thin filmsMalariaQuinine
PicaBasophilic stipplingWrist x ray—lead lineLead encephalopathyChelation
Blood cultureAllAppropriate antibiotics
Stool cultureAllShigella, enteroviruses
Mycoplasma IgG, IgMAll (unless cause known)Chest xrayMycoplasma encephalitisErythromicin, ?prednisolone
Viral titresAnalyse if unexplainedRepeat at discharge
Urine for toxin screenAnalyse if unexplainedBlood film—basophilic stipling, wristx ray—lead linePoisoningAntidote
Blood leadAnalyse if unexplainedChelation
CT scan without contrastAll (after resuscitation, afebrile patients should ideally be transferred for CT scan to a unit with neurosurgical facilities)Blood
• SubduralSkull x ray/skeletal survey/clotting screenNon-accidental injuryNeurosurgical referral
Child protection
• ExtraduralNeurosurgical referral
• Intracerebral
Space occupying lesionTumourNeurosurgical referral
• Obstructive ?Space occupying lesionAntituberculous cover
• Communicating CSF examination?Meningitis, especially tuberculousNeurosurgical referral
AbscessCulture aspirateNeurosurgical referral
Anaerobic cover
Contrast CT/MRI
SwellingMannitol 0.25 g/kg
Focal low densityCerebral abscess, herpes simplex, stroke, ADEM
Abnormal basal ganglia Plasma/CSF lactate, blood gasLeigh's syndrome, hypoxic-ischaemic, striatal necrosis
Lumbar punctureIn febrile if no clinical or radiological evidence of raised ICP (delay and treat if doubt)
• Pressure measurementHighCT scanMannitol, ventilate
• MicroscopyHigh WCCMeningitis/encephalitis3rd generation cephalosporin, aciclovir
• Gram, bacterial culture High RBCCT scan (traumatic tap should clear by 3rd bottle)Haemorrhage/encephalitis/ non-accidental injuryNeurosurgical referral, aciclovir, child protection
• GlucoseLowImmediate and prolonged
• ProteinHigh} Tuberculous meningitisantituberculous therapy
• PCR for viruses, TB
• Prolonged search for acid fast bacilli, culture for TB on Lowenstein–
Prodrome > 7 days, optic atrophy, focal signs, abnormal movements, CSF polymorphs < 50%, hydrocephalus and/or basal enhancement on contrast CTTuberculous meningitisImmediate and prolonged antituberculous therapy
• Antibodies e.g. herpes simplex, MycoplasmaEncephalitisAciclovir, erythromycin
• Lactate Abnormal breathing/eye movements, basal ganglia lucenciesMuscle biopsyLeigh's syndrome
EEGAll, especially if ventilated or evidence of subtle seizures (nystagmus, tonic deviation of eyes, clonic jerking limbs)Epileptiform dischargesStatus epilepticusIV benzodiazepines, phenytoin, thipentone
Asymmetrical foci of spikes or periodic lateralising epileptiform discharges on slow backgroundHerpes simplex encephalitis (many patients do not have characteristic EEG)High dose IV aciclovir for 2 weeks
MRIUnexplained encephalopathyFrontotemporal abnormalityCSF for herpes simplex PCRHerpes simplex encephalitisHigh dose IV aciclovir for 2 weeks
Thalamic abnormalityCSF for Epstein–Barr virus (arboviruses in endemic area)