Table 2.

Causality rating system adapted with modifications from Stausberg and Hasford^{21 22}

Code category	Definition	Examples
		Code	Code description
A1	The ICD-10 code description includes the phrase ‘induced by medication/drug’	J70.2	Acute drug-induced interstitial lung disorders
A2	The ICD-10 code description includes the phrase ‘induced by medication or other causes’	142.7	Cardiomyopathy due to drugs and other external agents
		T88.7	Unspecified adverse event of drug or medicament
B1	The ICD-10 code description includes the phrase ‘poisoning by medication’	T36	Poisoning by systemic antibiotics
B2	The ICD-10 code description includes the phrase ‘poisoning by or harmful use of medication or other causes’	X44	Accidental poisoning by, and exposure to, other and unspecified drugs, medicaments and biological substances
C	Adverse drug event deemed to be very likely although the ICD-10 code description does not refer to a drug	L51.2	Toxic epidermal necrolysis
D	Adverse drug event deemed to be likely although the ICD-10 code description does not refer to a drug	N17	Acute renal failure with tubular necrosis
E	Adverse drug event deemed to be possible although the ICD-10 code dictionary does not refer to a drug	K25	Gastric ulcer
U	Adverse drug event deemed unlikely	I49.0	Ventricular fibrillation and flutter
V	Vaccine-associated adverse event	A80.0	Acute paralytic poliomyelitis, vaccine-associated

The causality ratings were modified for the purposes of this systematic review. We added category U for ICD-10 codes that have been used by others to identify adverse drug events, but which we felt were unlikely to be adverse drug event related. We also added category V to indicate codes that may be vaccine-related.

ICD, International Classification of Diseases.