Re: Completeness and diagnostic validity of recording acute myocardial infarction events in primary care, hospital care, disease registry, and national mortality records: cohort study
We read with interest the article by Herrett and colleagues, reporting that a primary care database alone captured approximately 75% of all cases of acute myocardial infarction (Herrett, Figure 3). This could have implications for every study that has used primary care databases to derive, or validate, clinical prediction rules for cardiovascular disease.
For example, a study using The Health Improvement Network (THIN) database to evaluate cardiovascular risk equations reported that Framingham equations overestimated cardiovascular risk by 23% . The Framingham Investigators used a comprehensive standardised ascertainment method for cardiovascular outcomes  whereas THIN relies on similar data to the CPRD database studied by Herrett. The apparent discrepancy in accuracy between Framingham and cardiovascular events in this THIN study appears remarkably similar to the discrepancy in ascertainment reported by Herrett et al., albeit for MI alone rather than total cardiovascular risk. Subsequent external validations using THIN also reported that Framingham over estimated risk [3,4].
We suggest that the choice of risk score for use in clinical practice should ideally be based on head to head validation studies that have used linked methods, similar to those of Herrett, to establish event rates.
1. Collins GS, Altman DG. An independent external validation and evaluation of QRISK cardiovascular risk prediction: A prospective open cohort study. BMJ (Online). 2009;339(7713):144-7.
2. Shurtleff D: Some characteristics related to the incidence of cardiovascular disease and death: Framingham study, 16-year follow-up, in Kannel WB, Gordon T (eds): The Framingham Study: An Epidemiological Investigation of Cardiovascular Disease, section 26. US Government Printing Office No. 0-414-297, Washington, D.C.,1971
3. Collins GS, Altman DG. Predicting the 10 year risk of cardiovascular disease in the united kingdom: Independent and external validation of an updated version of QRISK2. BMJ (Online). 2012;345(7867).
4. Collins GS, Altman DG. An independent and external validation of QRISK2 cardiovascular disease risk score: A prospective open cohort study. BMJ (Online). 2010;340(7758):1231.
Competing interests: Richard Stevens is a member of the Independent Scientific Advisory Committee for MHRA database research. Both authors have used primary care databases in their research including CPRD, THIN and QRESEARCH.