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European Journal of Heart Failure 2008 10(7):658-660; doi:10.1016/j.ejheart.2008.05.006
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© 2008 European Society of Cardiology

Accuracy of a heart failure diagnosis in administrative registers

Thomas Kümlera,*, Gunnar Hilmar Gislasona, Vibeke Kirkb, Morten Bayc, Olav W. Nielsend, Lars Købere and Christian Torp-Pedersend

a Department of Cardiology, Copenhagen University Hospital Gentofte Niels Andersens Vej 65, 2900 Hellerup, Denmark
b Department of oncology, Copenhagen University Hospital Herlev Herlev Ringvej 75, 2730 Herlev, Denmark
c Department of Cardiology, Copenhagen University Hospital Frederiksberg Ndr. Fasanvej 57, 2000 Frederiksberg, Denmark
d Department of Cardiology, Copenhagen University Hospital Bispebjerg Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark
e Department of Cardiology B, 2141, Copenhagen University Hospital Rigshospitalet Blegdamsvej 9, 2100 Copenhagen, Denmark

* Corresponding author. E-mail addresses: tkumler{at}dadlnet.dk (T. Kümler), v.kirk{at}dadlnet.dk (V. Kirk), morten_bay{at}hotmail.com (M. Bay), own{at}dadlnet.dk (O.W. Nielson), lk{at}heart.dk (L. Køber), ctp{at}heart.dk (C. Torp-Pedersen).


   Abstract
Top
 Abstract
1. Background
 2. Aim
 3. Methods
 4. Results
 5. Conclusion
 References
 
Background: The incidence of heart failure is frequently reported using hospital discharge diagnoses. The specificity of a diagnosis has been shown to be high but the sensitivity of a reported diagnosis is unknown.

Purpose: To study the accuracy of a heart failure diagnosis reported to the Danish National Patient Registers during routine clinical work.

Methods: The patient population consisted of 3644 consecutive patients admitted to all departments in one hospital. Diagnoses reported to the National Patient Register were recorded. A study team evaluated each patient independently of routine care, performed an echocardiogram and evaluated whether clinical symptoms of heart failure were present. Heart failure was defined in accordance with current ESC guidelines as symptoms of heart failure and evidence of cardiac dysfunction.

Results: A registered diagnosis of heart failure (n=126) carried a specificity of 99% and a sensitivity of 29% for all patients. The positive predictive value was 81%, the negative predictive value 90%.

Conclusion: The diagnosis of Heart Failure in the Danish National Registers is underreported, but very specific.

Key Words: Accuracy • Heart failure • Diagnosis

Received September 29, 2007; Revised May 1, 2008; Accepted May 1, 2008


   1. Background
Top
 Abstract
 1. Background
2. Aim
 3. Methods
 4. Results
 5. Conclusion
 References
 
An increasing prevalence of heart failure (HF) has been documented using administrative registers [1,2]. This could be due to demographic factors, risk factors for HF, increased survival of patients with ischaemic heart disease, or changing recording habits. Due to the increased availability of administrative registries, it is important to examine if the discharge coding diagnosis of HF can be used for studies of incidence and prevalence of the disease.


   2. Aim
Top
 Abstract
 1. Background
 2. Aim
3. Methods
 4. Results
 5. Conclusion
 References
 
The aim of this study was to evaluate the accuracy of HF diagnosis reported in the Danish National Patient Register during routine clinical work. Data from a prospective study of all patients admitted to a single hospital were compared with the HF diagnosis from the Danish National Patient Register.


   3. Methods
Top
 Abstract
 1. Background
 2. Aim
 3. Methods
4. Results
 5. Conclusion
 References
 
The methods have been described in detail previously [3].

The study aimed to include all consecutive patients above the age of 40 years admitted to one hospital (n=3644) over a 12 month period starting from April 1st 1998. Four hundred and thirty patients (12%) were excluded due to: (1) discharge within 24 h after admittance (N=155); (2) death before inclusion (N=56); (3) mental or physical status not allowing examination (N=68); and (4) refusing to give consent (N=151). The remaining 3214 patients (88%) gave written informed consent, of these 13 patients (6 with aortic stenosis, 7 with pericardial effusion) were excluded due to echocardiographic findings showing a need for acute intervention. Blood samples were available for patients included in the study after June 1st, (N=2230, 80%). Echocardiographic measurements of left ventricular function could not be satisfactorily performed in 37 patients.

The study was conducted independently of the treatment of patients and clinicians were blinded to the data obtained in the study.

Patients were included consecutively from all departments in the hospital.

One of the study physicians (either Vibeke Kirk (V.K.) or Morten Bay (M.B.)) obtained a medical history and performed a clinical examination within 24 h of admission. The criteria for symptoms of heart failure were fatigue or shortness of breath at rest or during exercise. Clinical signs of heart failure were fluid accumulation or dyspnoea or need for diuretic therapy most likely explained by a cardiac condition. The other physician (V.K. or M.B.) then performed the echocardiographic evaluation. Both physicians were blinded to the results of the other's evaluation and the interobserver variation for echocardiographic evaluation of left ventricular ejection fraction was 4%. Following discharge, the physicians evaluated the patients together.

Registered heart failure (Reg-HF) corresponds to the primary or secondary diagnosis entered in the Danish National Patient Registry (ICD10, DI50.0-DI50.9) by the regular staff clinicians, who were blinded to the results obtained by the study staff.

Heart failure was defined as a patient with symptoms of heart failure and at least one echocardiographic abnormality. This definition is in accordance with the current ESC definition of heart failure [4]. Abnormal NT-proBNP by ELISA-assay (Roche, Basal) [5] was defined as ≥100 pmol/l, corresponding to the optimal value for diagnosing LVEF<35% in a previous study using the same assay [6].

All data were analysed by SAS, version 9.13 (SAS institute, Cary, NC), discrete variables by chi-square test and general linear models for continuous variables.

The study was approved by the regional ethics committee of the city of Copenhagen.


   4. Results
Top
 Abstract
 1. Background
 2. Aim
 3. Methods
 4. Results
5. Conclusion
 References
 
A total of 3201 patients were included in the study. Baseline characteristics according to the presence of heart failure compatible with the ESC criteria and/or recorded heart failure in the national hospital registry are shown in Table 1.


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  		Table 1 Characteristics of patients according to heart failure classification

 
One hundred and fifty six patients had Reg-HF of which 30 did not have ESC-HF, while-303 had ESC-HF but not Reg-HF.

Patients with ESC-HF with or without Reg-HF were older (p<0.001), had a higher serum creatinine (p<0,001), lower left ventricular ejection fraction (p<0.001), higher NT-proBNP (p≤0.001), and a greater proportion of cardiac abnormalities (p<0.001) compared to patients without ESC-HF. We found no significant difference with regard to haemoglobin level (p=NS), and systolic (p=NS) or diastolic blood pressures (p=NS).

A registered diagnosis of HF carried a specificity of 99% and a sensitivity of 29% for all patients. The positive predictive value was 81%, the negative predictive value 90% (all patients, Table 2).


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  		Table 2 2 by 2 tables demonstrating calculation of predictive values, sensitivity and specificity

 
Within different hospital departments the sensitivity/specificity of an HF diagnosis varied between 5/100% in the surgical department, 30/98% in the coronary care unit and 39/98% in the general medical ward.


   5. Conclusion
Top
 Abstract
 1. Background
 2. Aim
 3. Methods
 4. Results
 5. Conclusion
References
 
This study demonstrates that HF is severely underreported in the Danish National Hospital Register with a 29% sensitivity of HF discharge coding diagnosis. The independent evaluation was able to confirm a diagnosis compatible with the ESC criteria in 99% of reported cases. The sensitivity was a little higher in patients with low LVEF (39%).

To our knowledge, the present study is the first to systematically evaluate both the specificity and sensitivity of HF diagnosis in consecutively admitted patients to one hospital. A high specificity of a reported case of heart failure has been demonstrated in studies from Canada [7], Sweden [8] and the United Kingdom [9], similar to the current report. Hospital discharge codes substantially underestimate hospital events related to heart failure in the UK [9]. In the EuroHeart Failure survey, the sensitivity of HF diagnosis was 71% overall, but 53-59% in the northern European countries [10].

The implication of this study is that registers can be used to identify large groups of patients with HF for epidemiological studies, as the diagnosis accurately identifies patients with clinical HF. However, discharge coding diagnosis of HF is not suitable for use in studies of prevalence and incidence of HF in a population, as these codes severely underreport the magnitude of HF.


   References
Top
 Abstract
 1. Background
 2. Aim
 3. Methods
 4. Results
 5. Conclusion
 References
 

  1. Young J.B. The global epidemiology of heart failure. Med Clin North Am (2004) 88(5):1135–1143. [ix].[CrossRef][Web of Science][Medline]
  2. Cubillos-Garzon L.A., Casas J.P., Morillo C.A., Bautista L.E. Congestive heart failure in Latin America: the next epidemic. Am Heart J (2004) 147(3):412–417.[CrossRef][Web of Science][Medline]
  3. Kirk V., Bay M., Parner J., et al. N-terminal proBNP and mortality in hospitalised patients with heart failure and preserved vs. reduced systolic function: data from the prospective Copenhagen Hospital Heart Failure Study (CHHF). Eur J Heart Fail (2004) 6(3):335–341.[Abstract/Free Full Text]
  4. Swedberg K., Cleland J., Dargie H., et al. Guidelines for the diagnosis and treatment of chronic heart failure: executive summary (update 2005): The Task Force for the Diagnosis and Treatment of Chronic Heart Failure of the European Society of Cardiology. Eur Heart J (2005) 26(11):1115–1140.[Free Full Text]
  5. Karl J., Borgya A., Gallusser A., et al. Development of a novel, N-terminal-proBNP (NT-proBNP) assay with a low detection limit. Scand J Clin Lab Invest Suppl (1999) 230:177–181.[Medline]
  6. Groenning B.A., Raymond I., Hildebrandt P.R., Nilsson J.C., Baumann M., Pedersen F. Diagnostic and prognostic evaluation of left ventricular systolic heart failure by plasma N-terminal pro-brain natriuretic peptide concentrations in a large sample of the general population. Heart (2004) 90(3):297–303.[Abstract/Free Full Text]
  7. Lee D.S., Donovan L., Austin P.C., et al. Comparison of coding of heart failure and comorbidities in administrative and clinical data for use in outcomes research. Med Care (2005) 43(2):182–188.[CrossRef][Web of Science][Medline]
  8. Ingelsson E., Arnlov J., Sundstrom J., Lind L. The validity of a diagnosis of heart failure in a hospital discharge register. Eur J Heart Fail (2005) 7(5):787–791.[Abstract/Free Full Text]
  9. Khand A.U., Shaw M., Gemmel I., Cleland J.G. Do discharge codes underestimate hospitalisation due to heart failure? Validation study of hospital discharge coding for heart failure. Eur J Heart Fail (2005) 7(5):792–797.[Abstract/Free Full Text]
  10. Cleland J.G., Swedberg K., Follath F., et al. The EuroHeart Failure survey programme — a survey on the quality of care among patients with heart failure in Europe. Part 1: patient characteristics and diagnosis. Eur Heart J (2003) 24(5):442–463.[Abstract/Free Full Text]

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