BACKGROUND: The novel simplified out-of-hospital cardiac arrest (sOHCA) and 
simplified cardiac arrest hospital prognosis (sCAHP) scores used for 
prognostication of hospitalised patients have not been externally validated. 
Therefore, this study aimed to externally validate the sOHCA and sCAHP scores in 
a Japanese population.
METHODS: We retrospectively analysed data from a prospectively maintained 
Japanese database (January 2012 to March 2013). We identified adult patients who 
had been resuscitated and hospitalised after intrinsic out-of-hospital cardiac 
arrest (OHCA) (n=2428, age ≥18 years). We validated the sOHCA and sCAHP scores 
with reference to the original scores in predicting 1-month unfavourable 
neurological outcomes (cerebral performance categories 3-5) based on the 
discrimination and calibration measures of area under the receiver operating 
characteristic curves (AUCs) and a Hosmer-Lemeshow goodness-of-fit test with a 
calibration plot, respectively.
RESULTS: In total, 1985/2484 (82%) patients had a 1-month unfavourable 
neurological outcome. The original OHCA, sOHCA, original cardiac arrest hospital 
prognosis (CAHP) and sCAHP scores were available for 855/2428 (35%), 1359/2428 
(56%), 1130/2428 (47%) and 1834/2428 (76%) patients, respectively. The AUCs of 
simplified scores did not differ significantly from those of the original 
scores, whereas the AUC of the sCAHP score was significantly higher than that of 
the sOHCA score (0.88 vs 0.81, p<0.001). The goodness of fit was poor in the 
sOHCA score (ν=8, χ2=19.1 and Hosmer-Lemeshow test: p=0.014) but not in the 
sCAHP score (ν=8, χ2=13.5 and Hosmer-Lemeshow test: p=0.10).
CONCLUSION: The performances of the original and simplified OHCA and CAHP scores 
in predicting neurological outcomes in successfully resuscitated OHCA patients 
were acceptable. With the highest availability, similar discrimination and good 
calibration, the sCAHP score has promising potential for clinical 
implementation, although further validation studies to evaluate its clinical 
acceptance are necessary.