Investigations
1st investigations to order
serum electrolytes
Test
Hypokalaemia suggests ingestion of sympathomimetics or barium salts and is frequently accompanied by hypomagnesaemia.
Hyperkalaemia suggests ingestion of digoxin or fluoride-based cleaning products.
Hyponatraemia suggests use of amfetamines or methylxanthines.
Hypocalcaemia suggests fluoride toxicity or ethylene glycol.
Result
normal; hypokalaemia with or without hypomagnesaemia; hyperkalaemia; hyponatraemia; hypocalcaemia
serum urea
Test
Acute kidney injury can occur either due to overdoses that are directly nephrotoxic or as a result of rhabdomyolysis from prolonged seizures, hypotension, or acidosis.
Result
elevated in acute kidney injury
serum creatinine
Test
Acute kidney injury can occur either due to overdoses that are directly nephrotoxic or as a result of rhabdomyolysis from prolonged seizures, hypotension, or acidosis.
Those assays that use the Jaffe reaction to determine creatinine can have a falsely elevated creatinine in the presence of ketones.
Result
elevated in acute kidney injury
fingerprick or serum glucose
Test
Hypoglycaemia suggests poisoning with insulin, sulfonylureas, beta-blockers, or severe salicylate poisoning.
Hyperglycaemia suggests calcium-channel blocker or theophylline poisoning.
Result
normal, elevated, or reduced
capillary blood gas or ABG
Test
A capillary blood gas or ABG helps to establish the cause of an increased anion gap acidosis.
Metabolic acidosis is seen in salicylate, toxic alcohol, or iron poisoning due to direct effects on metabolism, or in sympathomimetic or theophylline poisoning due to end-organ ischaemia.
Hypoxaemia with or without respiratory acidosis from hypoventilation is seen in opioid or clonidine poisoning.
Respiratory alkalosis is seen in salicylate poisoning before the onset of metabolic acidosis.
Result
normal or shows metabolic acidosis, respiratory acidosis, respiratory alkalosis, or hypoxaemia
anion gap
Test
May be raised due to lactate, ketones, or ingested toxic alcohols.
Result
normal or increased
serum lactate
Test
Elevated in metabolic acidosis produced by agents that interfere with metabolism or produce ischaemia.
Glycolic acid may interfere with the lactate measurement.
Result
normal or elevated
serum ketones or acetone
Test
Ketone formation is seen with starvation and may be seen with an overnight fast, especially if glycogen stores are low. It is also seen in salicylate poisoning and chronic abuse of alcohol in children.
Result
normal or elevated
INR
Test
An increased INR suggests poisoning with warfarin, another coumarin rodenticide, or a hepatotoxin (e.g., paracetamol).
Result
normal or increased
LFTs
Test
Used primarily to monitor the progression of hepatotoxicity.
Abnormal LFTs indicate ingestion of a hepatotoxin, usually paracetamol.
Results should be interpreted in the context of the INR. Improving LFTs in the face of a rising INR and rising total bilirubin suggest fulminant hepatic necrosis.
Result
normal or increased
serum paracetamol levels
Test
Should be performed in all patients 4 hours after the time of the suspected ingestion. The level of serum paracetamol relative to the time of ingestion will determine the need for subsequent treatment. The graph used to assess serum levels varies between countries, and physicians should consult the local paracetamol overdose protocols. In the UK, a treatment graph that covers normal and high-risk patients is used, whereas in the US, the Rumack-Matthew nomogram is widely used, and a similar guideline is used in Australia and New Zealand.[36][37]
The diagnosis of paracetamol toxicity based on the Rumack-Matthew nomogram is reserved for single acute ingestions of paracetamol. It cannot be used before 4 hours or after 24 hours.
The following cases should be discussed with a regional poison control centre or a paediatric toxicologist: children with repeated supratherapeutic ingestions of paracetamol, repeated ingestions over time, co-ingestion with drugs that alter gastric motility such as opioids or antimuscarinic medications, co-ingestion with ethanol, ingestion of sustained-release paracetamol products, ingestions occurring 24 hours or more before presentation, or when the time of ingestion is unknown, because nomograms such as the Rumack-Matthew nomogram cannot be used in these circumstances.[Figure caption and citation for the preceding image starts]: Paracetamol treatment graph. This consists of a normal treatment line, which connects 1.32 mmol/L (200 mg/L) at 4 hours and 0.04 mmol/L (6.25 mg/L) at 24 hours, and a high-risk treatment line for those at increased risk of liver damage, which connects the points at 50% of the plasma paracetamol concentrations of the normal line. Patients should be treated if their plasma paracetamol concentration is above their appropriate treatment lineWith permission of Professor P.A. Routledge, Therapeutics and Toxicology Centre, Cardiff University [Citation ends].
Result
negative or level detected
serum salicylate levels
Test
Should be performed in all patients with an intentional overdose, due to the ubiquity and fatality of these ingestants.
A positive result is seen in acute salicylate poisoning, but a negative result may be seen in sub-acute or chronic poisoning. For this reason, the diagnosis should be based both on clinical features and on laboratory findings, including the results of ABG analysis.
Result
negative or level detected
urine drug screen
Test
A urine drug screen should be performed in all children with a deliberate or suspected ingestion. However, the limitations of these tests need to be appreciated. A screen may cover ingested, injected, and inhaled drugs. A range of screening assays are available, which typically cover varying numbers of commonly misused substances such as amfetamines, cocaine, phencyclidine (PCP), cannabinoids, and opioids. If a category is reported (e.g., opioids), it is important to inquire which specific substances (e.g., opium, codeine, heroin, morphine) are actually detected as some specific compounds may be excluded.
Additional testing can be ordered if needed for any substances of interest that are not covered by a given urine drug screen.
The tests are usually immunoassays that screen for a group of substances within a class of medications, and, therefore, may identify false positives (e.g., the cough suppressant dextromethorphan can give a false positive on the PCP assay). Conversely, a negative result does not exclude the presence of the drug.
The results should be interpreted in the context of clinical findings and may require confirmatory testing in legal cases.
Result
identification of select drugs of misuse (available results will vary depending on which drug screen is utilised)
urinalysis
Test
Calcium oxalate crystals should prompt measurement of serum ethylene glycol.
Rhabdomyolysis may be due to prolonged seizures, hypotension, or acidosis.
Result
calcium oxalate crystals in ethylene glycol poisoning; haem without red blood cells in rhabdomyolysis; brown discoloration in phenol poisoning
ECG
Test
Certain ST-T changes and rhythms are consistent with digoxin poisoning.
An R-wave in aVR and an S wave in I and aVL are early signs of sodium channel blockade, which progress to widening of the QRS complex. Tricyclic antidepressants are the most common causative agents.
QT prolongation suggests potassium-channel blockers (neuroleptics, methadone and other opioids, arsenic), calcium-channel blockers, or hypocalcaemia.
Bradycardia suggests alpha-2 agonists, calcium-channel blockers, beta-blockers, digoxin, or cholinergics.
Result
normal or characteristic changes of causative agent; arrhythmias
pregnancy test
Test
It is important to be aware of the presence of pregnancy when treating a toxic ingestion, as the treatment threshold for certain poisonings may be low. Treatment of the mother is usually sufficient to treat the fetus and takes precedence in therapy.
Result
exclude pregnancy in a girl of reproductive age
serum creatine kinase
Test
An elevated creatine kinase indicates rhabdomyolysis, which may be due to prolonged seizures, hypotension, or acidosis.
Aspartate aminotransferase is also frequently elevated in rhabdomyolysis.
Result
elevated in rhabdomyolysis
abdominal x-ray
Test
Radio-opaque medications and toxins include iron, heavy metals, certain chlorinated hydrocarbons, enteric-coated pills, and phenothiazines.
Result
radio-opaque bodies in the gastrointestinal tract in heavy metal or foreign body ingestion
chest x-ray
Test
Should be performed in patients with severe respiratory symptoms or in whom aspiration is suspected.
Hydrocarbon ingestions require a repeat chest x-ray 6 hours from ingestion if an initial one is done soon after the ingestion. In this case, initial radiographic findings may not be evident soon after the exposure. Interval development of infiltrate or respiratory symptoms should prompt admission.
Result
normal or signs of pulmonary oedema or aspiration
Investigations to consider
ethanol level
Test
Should be considered in older children suspected of substance misuse. Any detectable level of ethanol using serum alcohol levels is diagnostic. There are situations that may cause a false positive with a breathalyser.
Result
negative or level detected
serum methanol or ethylene glycol
Test
Should be measured if clinical symptoms suggest these poisonings or if there is an anion gap on ABG that is not explained by lactate or ketones. Ethylene glycol levels should also be measured if calcium oxalate crystals are found on urine examination.
Result
negative or level detected
serum digoxin level
Test
Should be considered if digoxin toxicity is suspected based on the clinical features, presence of hyperkalaemia, or ECG findings.
Result
negative or level detected
serum anticonvulsant levels
Test
Should be considered if toxicity due to phenobarbital, phenytoin, valproate, or carbamazepine is suspected.
Result
negative or level detected
serum iron levels
Test
Levels should be measured 4 hours post-ingestion. Levels taken >6 hours post-ingestion may underestimate toxicity. Lower serum iron levels cannot eliminate the possibility of toxicity.
Result
normal or elevated iron
serum lithium, theophylline, or whole blood heavy metal levels
Test
Levels should be obtained if poisoning with any of these agents is suspected.
Some metal poisonings may require urine levels.
Result
negative or positive for ingested substance
comprehensive urine drug screen
Test
May be considered as a confirmatory test.
Designed to test for several hundred medications using a sensitive and specific method, but it is time-consuming.
The results should be interpreted in the context of the clinical features.
Result
identification of ingested substances
therapeutic trial of naloxone
Test
Should be given if features of the opioid toxidrome are present and there is evidence of respiratory depression; a positive response may be diagnostic of opioid ingestion, but may sometimes be seen in clonidine ingestion.
Should not be given if the patient is intubated.
Result
positive response in opioid or alpha-2 agonist ingestion
therapeutic trial of sodium bicarbonate
Test
Should only be given in consultation with an expert experienced in the management of poisoning in children.
If the QRS does not narrow, or symptoms do not improve, check the serum pH to ensure that the pH is between 7.45 and 7.55. If it is not, repeat dosing.
Result
narrowing of the QRS in sodium-channel blocker toxicity; improvement in symptoms in salicylate poisoning
therapeutic trial of atropine and pralidoxime
Test
Should be given if there are features of the cholinergic toxidrome, in consultation with an expert in the management of poisoning in children.
Result
positive response in cholinesterase inhibitor poisoning
therapeutic trial of flumazenil
Test
May be considered if there are clinical features of the sedative-hypnotic toxidrome in patients who are not chronically taking benzodiazepines and withdrawal is not a concern. This should be given in consultation with an expert experienced in the management of poisoning in children.
Result
positive response in benzodiazepine poisoning
therapeutic trial of octreotide
Test
May be given if there is hypoglycaemia suspected to be due to sulfonylurea toxicity or massive insulin injection. This should be given in consultation with an expert experienced in the management of poisoning in children.
Result
improvement in blood glucose levels
therapeutic trial of physostigmine
Test
Consider in cases with signs of peripheral and central antimuscarinic features in appropriate patients.
Expert consultation before using physostigmine for these patients is recommended as its use in some poisonings (e.g., tricyclic antidepressants) may be contraindicated.
Result
improvement in mental status or peripheral antimuscarinic symptoms
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