This calculator is a faithful replication of the Non-Laboratory INTERHEART Risk Score (NL-IHRS), given website developer's technical ability, as externally validated in the PURE (Prospective Urban Rural Epidemiology) study — a community-based prospective cohort of over 140 000 participants across 17 countries and 7 geographic regions.
The underlying research was led by Dr Philip Joseph (first author, Population Health Research Institute, McMaster University, Hamilton, Canada — a cardiologist and clinical trialist whose work focuses on global cardiovascular epidemiology) and Professor Salim Yusuf (senior / corresponding author, McMaster University — one of the most cited cardiovascular researchers in the world, principal investigator of the landmark INTERHEART, PURE, and HOPE trials, and a recipient of the Order of Canada). The validation cohort spans high-, middle-, and low-income countries, making the score uniquely suited for diverse populations.
Our implementation faithfully reproduces the Prognostic Index (PI) for a given set of risk-factor point totals using the original INTERHEART regression coefficients published in the paper:
Equation [3] — Estimated Prognostic Index from total points:
estimated PI = −1.45 + 0.2875 × (NL-IHRS total points / 2)
Region-specific recalibration is then applied using the intercept (α̂) and slope (β̂) measured in each PURE region (Table 2 of the paper), producing the final predicted probability:
Equation [4] — Recalibrated CVD risk:
p̂ = 1 / { 1 + exp[ −( α̂ + β̂ × estimated PI ) ] }
Following recalibration, the score achieved a C-statistic of 0.72 (95 % CI 0.71–0.73) in the overall PURE population — moderate-to-good discrimination across all seven regions — and was only marginally outperformed by the laboratory-based FC-IHRS (C-statistic 0.74 vs 0.73, p < 0.001).
References
Joseph P, Yusuf S, Lee SF, et al. Prognostic validation of a non-laboratory and a laboratory based cardiovascular disease risk score in multiple regions of the world. Heart 2018;104:581–587. doi:10.1136/heartjnl-2017-311609.