Original ArticleVenous thromboembolism discharge diagnoses in the Danish National Patient Registry should be used with caution
Introduction
Venous thromboembolism (VTE), that is, deep venous thrombosis (DVT) and pulmonary embolism (PE) is a common disease, with substantial clinical implications. Patients with VTE have a mortality of 16–21% the first year after diagnosis; the cumulative incidence of recurrent VTE is 30% and of postthrombotic syndrome is 29% after 8 years of follow-up [1], [2], [3], [4]. Possible risk factors for VTE, identified in recent cohort studies [2], [5], [6], [7], [8], [9], [10], [11], include both genetic predispositions and acquired factors. However, 25–50% of VTE events remain idiopathic, underscoring the need for well-designed studies elucidating the causes of this disease.
Hospital discharge registries are a potentially valuable source of data on VTE [12], with data readily available at low cost. Routine data collection and often universal registration of people in the target population help avoid biases of recall, diagnosis, or selection. However, lack of investigator's control over data collection and quality are important disadvantages of registry data [12], [13]. Quality of registry data varies considerably from disease to disease and poor data quality may invalidate results of epidemiologic studies. Thus, it is essential to validate routinely collected registry data before using them for research. Few studies have examined the data quality of VTE diagnoses in registries in selected patient groups [14], [15], [16], [17]. Validation was done only by secondary diagnoses to determine the frequencies of in hospital-acquired VTE by others [18], [19]. We aimed to determine the positive predictive value (PPV) of VTE diagnoses in the Danish National Patient Registry, a nationwide hospital discharge register.
Section snippets
The Diet, Cancer, and Health study
Diet, Cancer, and Health is a prospective cohort study, with the primary objective to investigate the etiologic role of diet in the development of cancer. The study has been described in detail elsewhere [20], [21]. Briefly, between December 1993 and May 1997, 80,996 men and 79,729 women, aged 50–64 years, were invited to participate in the study; 27,178 men and 29,876 women accepted the invitation. Eligible cohort members were born in Denmark, were living in the urban areas of Copenhagen and
Validation of VTE diagnoses in the Danish National Patient Registry
Figure 1 shows the results of the review of medical records. We identified 1,135 participants in the Diet, Cancer, and Health cohort study with a first-time VTE diagnosis recorded in the Danish National Patient Registry during the follow-up period. We were able to retrieve the medical records from 1,100 (96.9%) of these admissions. Of the 1,100 VTE diagnoses, 454 were given in emergency departments (Fig. 2). All but 36 patients were discharged into a ward unit within 1 week (n = 418). Of these,
Discussion
The PPV varied according to the subdiagnoses (DVT and PE), types of diagnoses (primary or secondary), type of hospital department, and gender. The highest (up to 87%) PPVs were found for PE diagnoses, in particular if it was a primary diagnosis; for diagnoses coded at wards (in contrast to emergency departments); and for diagnoses among men.
A number of other studies have examined the quality of VTE diagnoses in administrative databases [14], [15], [16], [17], [18], [19]. Two studies estimated
References (24)
- et al.
Incidence and mortality of venous thrombosis: a population-based study
J Thromb Haemost
(2007) - et al.
Deep vein thrombosis and pulmonary embolism in two cohorts: the longitudinal investigation of thromboembolism etiology
Am J Med
(2004) - et al.
Accuracy of coding for possible warfarin complications in hospital discharge abstracts
Thromb Res
(2006) - et al.
A review of medical records and discharge summary data found moderate to high predictive values of discharge diagnoses of venous thromboembolism during pregnancy and postpartum
J Clin Epidemiol
(2005) - et al.
ICD-9-CM codes poorly indentified venous thromboembolism during pregnancy
J Clin Epidemiol
(2004) - et al.
The validity of ICD-9-CM codes in identifying postoperative deep vein thrombosis and pulmonary embolism
Jt Comm J Qual Patient Saf
(2007) - et al.
Predictive values of acute coronary syndrome discharge diagnoses differed in the Danish National Patient Registry
J Clin Epidemiol
(2009) Natural history of venous thromboembolism
Circulation
(2003)- et al.
The long-term clinical course of acute deep venous thrombosis
Ann Intern Med
(1996) The epidemiology of venous thromboembolism
Circulation
(2003)