Abstract
Shah AS, Griffiths M, Lee KK et al. BMJ 2015; 350: g7873.
Shah and colleagues used a high sensitivity cardiac troponin I assay to investigate the impact of using gender-specific 99th percentiles on myocardial infarction incidence. The group looked at the classification of 1126 patients (504 female, 622 male) with symptoms of acute coronary syndrome as having/had a type 1 myocardial infarction using a standard (less sensitive) troponin I assay with a single, gender-independent threshold (50 ng/L). The patients were then reclassified using a high sensitivity troponin I assay with gender-specific thresholds (females: 16 ng/L, males: 34 ng/L). Using the standard assay, 11% of the females and 19% of the males were classified as having/had type 1 myocardial infarction. Using the high sensitivity assay and the gender-specific thresholds, 11% more females but only 2% more males were identified as having/had a type 1 myocardial infarction.
Shah et al. also followed the death and reinfarction rates in the study participants over 12 months. This showed that the significant number of additional women identified as having/had myocardial infarction using only the high sensitivity assay had similar clinical outcomes to those women diagnosed with myocardial infarction using the standard assay. These additional women also had significantly increased death and reinfarction rates compared to those women stratified as ‘no myocardial infarction’ by the high sensitivity assay. The group also demonstrated that although the same proportion of men and women report chest pain and have ECG changes, women are less likely to be diagnosed with and treated for myocardial infarction. The authors suggest that the under-diagnosis of myocardial infarction in women is due to the use of inappropriate diagnostic thresholds.
Women, possibly due to their smaller ventricular mass, have twofold lower circulating levels of cardiac troponin than men. This difference was not discernable using standard assays due to their lack of analytical sensitivity and precision. Shah et al. have demonstrated that by using a single diagnostic cut off, even with a high sensitivity assay, women are significantly under-diagnosed with myocardial infarction. This paper showed that the proportion of myocardial infarction diagnoses in men and women became similar when a lower diagnostic threshold for women was used. This paper therefore suggests that using gender-specific thresholds will correctly identify more high-risk women, improve their long-term outcomes and reduce gender inequalities in the management and treatment of myocardial infarction.