European Journal of Heart Failure

European Journal of Heart Failure 2005 7(5):792-797; doi:10.1016/j.ejheart.2005.04.001

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© 2005 European Society of Cardiology

Do discharge codes underestimate hospitalisation due to heart failure? Validation study of hospital discharge coding for heart failure

Aleem U. Khand^a, Morag Shaw^a, Islay Gemmel^b and John G.F. Cleland^c,*

^a Department of Cardiology, Glasgow Royal Infirmary University of Glasgow, UK
^b Social and Public Health Sciences Unit University of Glasgow, UK
^c Department of Cardiology, University of Hull, UK

^* Corresponding author. Academic Unit of Cardiology, Castle Hill Hospital, Castle Road, Kingston-upon-Hull, HU16 5JQ, United Kingdom. E-mail address:J.G.Cleland{at}hull.ac.uk

	Abstract

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
Background: Discharge codes are frequently used to describe hospital activity related to heart failure (HF).

Objectives: To determine whether discharge codes for HF underestimated or overestimated hospital activity related to HF.

Design: Patients with atrial fibrillation (AF), who commonly have HF, were identified and their case notes reviewed to identify cases of HF missed by discharge codes.

Participants and methods: Patients admitted between November 1997 and January 1998 with either HF or AF. Identification of HF and AF by ICD10 hospital discharge codes. Identification of additional cases of AF from a central hospital-wide ECG database.

Results: We identified 330 cases with an ICD 10 code for HF, of which 43 (13%) were deemed to be miscoded, 32 patients (10%) were classified as possible, 39 (12%) as probable and 216 (65%) as definite HF. Results were similar whether or not HF was the primary discharge diagnosis. We identified 452 patients with AF, of whom 45 (10%) were classified as probable and 193 (43%) as definite HF. 129 (54%) of these cases had no diagnostic discharge code for HF. ICD 10 discharge codes for HF were correct in 77% of cases but identified only 66% of patients with probable or definite HF in this analysis. Screening of other diagnoses would have identified further cases of HF.

Conclusions: Hospital discharge codes substantially underestimate hospital events related to HF in the UK.

Key Words: Heart failure • Epidemiology • Hospital discharge coding

Received December 14, 2004; Accepted April 6, 2005

	1. Introduction

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
Hospital discharge codes are a valuable and easily accessible source of information on the disease burden attributable to a number of common diseases that require periods of inpatient care. Interrogation of large databases containing ICD (international classification of diseases) codes has often been used to determine disease trends, undertake economic analyses and to gain insight into the nature or mechanism of heart failure [1–3]. This information is a potent source of evidence for determining allocation of health resources [4]. However, there is relatively little published evidence regarding the accuracy of a hospital discharge diagnosis of heart failure or on the number of cases missed by their use.

We investigated the validity of using hospital discharge coding for a diagnosis of heart failure hospitalisation. Review only of admissions with a hospital discharge code for heart failure will identify false-positive coding but will fail to determine the number of missed cases (or false-negative codes). Therefore, in order to determine whether the diagnosis of heart failure was missed frequently, we reviewed all hospital admissions with atrial fibrillation (AF), a common co-morbidity of heart failure [5].

	2. Participants and methods

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
Glasgow Royal Infirmary is a teaching hospital serving a local population of 153,000. All hospital death and discharges from Glasgow Royal Infirmary and affiliated hospitals, principally a geriatric unit, between November 1997 and January 1998 inclusive were included. Patients with heart failure were identified by an ICD 10 discharge code for heart failure in any of the 6 diagnostic positions. The codes used were the following: Congestive heart failure, 150.1 Left ventricular failure, 150.2 Heart failure, unspecified, 111.0 Hypertensive heart failure, 111.1 Dilated cardiomyopathy, 125.5 Ischaemic cardiomyopathy, 142.9 Cardiomyopathy unspecified. Patients with AF were identified from ICD10 code 148X. A central database of in-patient electrocardiograms (ECGs) was used to identify further patients with a baseline rhythm of AF who did not have a code for AF.

The notes of all patients with a discharge code for heart failure or AF or an ECG diagnosis of AF were then retrieved and scrutinised to determine the presence of heart failure symptoms and the results of relevant investigations. Further data were acquired by searching databases of the radiology, echocardiography and nuclear medicine departments. Digitised ECGs for all patients were retrieved from a database to verify the presence of AF and to use as an additional check to assess the presence of ventricular dysfunction [6]. Significance between various groups was analysed as described by Fleiss et al. [7].

	3. Criteria for classifying likelihood of heart failure

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
European Society of Cardiology working group guidelines for the diagnosis of heart failure were used as diagnostic criteria [8] where both symptoms and objective evidence of important cardiac dysfunction are necessary for the diagnosis. The response to appropriate therapy was not part of the diagnostic criteria but conferred added weight to any diagnosis of heart failure.

	4. Symptoms of heart failure

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
Symptoms of heart failure included the following: Dyspnoea, exercise intolerance, orthopnoea and peripheral oedema. Case notes were scrutinised for the presence of symptoms and signs either on admission or from scrutiny of previous admissions or from correspondence with general practitioners. The presence of symptoms, at some point in time, was necessary to diagnose heart failure. Patients admitted for non-cardiovascular reasons, who were asymptomatic, but had been prescribed diuretics or ACE inhibitors for either of the above symptoms in the past fulfilled this criterion.

	5. Objective evidence of cardiac dysfunction

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
The probability of heart failure was graded according to whether investigations assessing cardiac function were carried out and the quality of these investigations. Therefore if a chest X-ray suggested cardiomegaly but the echocardiogram was normal, evidence from the former was ignored [9]. Patients were grouped into either no heart failure, possible, probable or definite heart failure or asymptomatic left ventricular systolic dysfunction.

No heart failure: Either: (a) no evidence of cardiac dysfunction and no symptoms of heart failure at any time or (b) symptoms consistent with heart failure but objective evidence of normal cardiac function (echocardiography, radionuclide ventriculography or ventricular angiography).

Possible heart failure: Symptoms of heart failure (and response to therapy) with or without cardiomegaly (on Chest X-ray) but no objective test of cardiac function undertaken.

Probable heart failure (ventricular function unknown): Symptoms of heart failure and cardiomegaly (Cardio-thoracic ratio>0.5) and bilateral pleural effusions on chest X-ray (in the absence of other possible pathology).

Definite heart failure (ventricular function unknown): Symptoms of heart Failure and alveolar or interstitial pulmonary oedema on chest X-ray in absence of other obvious explanation.

Definite heart failure due to left ventricular systolic dysfunction: Symptoms of heart failure in combination with any of the following:

Echocardiography: Written or typed report stating evidence of LV systolic dysfunction or dilated left ventricle (left ventricular end diastolic diameter of > 60 mm) or calculated or estimated ejection fraction of < 40% or WMI (wall motion index) score of less than 1.3.

Radionuclide ventriculogram: Report stating evidence of LV systolic dysfunction or left ventricular ejection fraction (LVEF) of less than 35% (cut-of for normal value in Glasgow Royal Infirmary).

Ventricular angiography: Report stating evidence of LV systolic dysfunction or estimated or calculated ejection fraction of less than 40%.

Definite heart failure due to valvular heart disease: Symptoms of heart failure and evidence of severe valvular lesion (regurgitation or stenosis) in the absence of significant left ventricular systolic dysfunction.

Definite heart failure with preserved left ventricular systolic dysfunction: This required the symptom criteria to be fulfilled, the absence of an obvious alternative cause for symptoms and the presence of a dilated left atrium [10], and preserved ventricular systolic function together with at least one of the following:

1. Left ventricular hypertrophy (either reported or inter-ventricular septum and posterior wall 11 mm).
   
2. Any abnormality in left ventricular inflow patterns. AF by definition constituted an abnormality in left ventricular filling.
   

When neither left ventricular hypertrophy nor abnormal left ventricular inflow patterns was present then only a diagnosis of probable heart failure with preserved ventricular systolic function could be made.

All patients had their ECG's scrutinised. If the ECG was normal then the diagnosis of heart failure was re-evaluated.

	6. Results

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
In total 791 case records were screened for the presence of heart failure (Table 1). 131 notes were screened twice; in the initial check of all patients with a HF code and subsequently as part of the process of screening all patients with AF for the presence of heart failure. Six hundred and sixty patients were admitted for or with heart failure or had AF (339 with a HF code and 321 with AF in the absence of an HF code). This constituted 24% of all medical admissions including geriatric admissions and 8% of all admissions. 29 records were screened twice in a blinded fashion to check for consistency of categorisation of heart failure. 28/29 were assigned the same status of heart failure (97% agreement).

View this table: [in this window] [in a new window]   Table 1 Characteristics and investigations of patients screened for heart failure

 
6.1. Heart failure discharge codes
Of 370 patients with a discharge code for heart failure, case notes on 339 were retrieved and scrutinised (92% retrieval rate). These 339 patients generated 407 admissions in the 3 months of study. This represented 5% of all admissions and 15% of admissions to all medical wards (including geriatric wards). Of the 339 patients there were only nine patients in whom it proved impossible to verify the presence or absence of heart failure symptoms either before or during admission because of inadequate documentation of events.

6.2. Accuracy of coding for heart failure
274 (83%) patients with an ICD 10 code for heart failure had an objective measure of ventricular function and a further 43 (13%) had at least a chest X-ray. Only 4% of patients had no assessment of cardiac dysfunction (Table 1). Fig. 1 illustrates the evidence for ventricular dysfunction in those assigned a discharge code for heart failure. 158 (48%) of the population had cardiomegaly on chest X-ray and 50 (15%) had evidence of acute pulmonary oedema. 267 (81%) patients were administered diuretics with documented symptom improvement in 221 patients (67%). 229 (69%) patients had evidence of left ventricular systolic dysfunction on echo, radionuclide ventriculography or left ventricular angiography.

View larger version (7K): [in this window] [in a new window] [Download PowerPoint slide]   Fig. 1 Evidence for left ventricular dysfunction in patients with a heart failure discharge code. LVSD: left ventricular systolic dysfunction, LVSF: left ventricular systolic function, Pulm oedema: pulmonary oedema.

 
Of the 330 patients with a diagnostic code for heart failure, 31 (9%) had no evidence of heart failure or LV systolic dysfunction and 13 patients had asymptomatic ventricular systolic dysfunction (4% of total) (Table 2). 31 patients (9%) had possible heart failure, 39 (12%) had probable heart failure and 216 (65%) had definite heart failure. This indicated an accuracy of 87% for ICD 10 discharge codes for heart failure if possible, probable and definite heart failure were allowed or 77% for probable or definite heart failure.

View this table: [in this window] [in a new window]   Table 2 Relationship of certainty of heart failure diagnosis to coding position

 
70% (237 patients) of HF discharge codes were in position 1 or 2 (Table 2). Coding position did not significantly influence accuracy of a code for heart failure. (p=0.3 for difference between accuracy of coding positions).

6.3. Screening of the atrial fibrillation population (Fig. 2)
325 patients had a discharge code for AF and case-notes of 314 were retrieved (97% retrieval rate). 170 patients had no discharge code for AF but had AF on their ECG and case-notes of 138 were retrieved (81% retrieval rate). Of the 452 patients identified by ECG or ICD 10 coding, there was insufficient information to assess heart failure status in 18 patients (4%).

135 (31%) patients had no evidence of heart failure, 44 (10%) had possible heart failure, 45 (10%) probable heart failure and 193 (45%) definite heart failure. 16 (4%) patients had asymptomatic left ventricular systolic dysfunction (LVSD). 155 of 193 (80%) patients with definite heart failure had LVSD, of whom 89 (57%) were receiving diuretics. 49 patients (11%) with AF had symptoms of heart failure but no investigations undertaken to confirm or refute left ventricular dysfunction.

Of the 238 patients with probable or definite HF identified by screening for AF, 129 (54%) were found to have no discharge code for HF. (Table 3; Fig. 2) Therefore, using only HF discharge codes and the presence of AF, 384 patients were identified during 3 months with probable or definite and 451 with possible, probable or definite HF. Hospital discharge coding identified only 66% of cases of probable or definite HF and underestimated HF admissions by between 16% (probable or definite HF) and 36% (possible, probable and definite HF) using only AF, as an additional risk marker, for heart failure.

View this table: [in this window] [in a new window]   Table 3 How patients with heart failure were identified

 

View larger version (9K): [in this window] [in a new window] [Download PowerPoint slide]   Fig. 2 Probable or definite HF in the AF population.

 
Compared to patients in whom a discharge code for heart failure had been missed, those patients receiving a correct discharge code were more likely to have ischaemic heart disease and more likely to have suffered a clinically overt exacerbation of heart failure in hospital (Table 4). Patients' age, sex or, surprisingly, admission ward did not explain coding practice.

View this table: [in this window] [in a new window]   Table 4 Characteristics of coded versus non-coded patients with probable or definite heart failure

 

	7. Discussion

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
This analysis suggests that the use of hospital discharge codes underestimates rather than overestimates admissions for or complicated by heart failure. Had this analysis been extended to all admissions, additional cases would certainly have been identified, although probably with a much lower percentage yield for many diagnoses other than AF [11]. Although the general accuracy of hospital morbidity records has been studied [12] as far as we are aware, no previous study has assessed the validity of using hospital discharge coding for heart failure hospitalisation.

These results have important implications. Estimates of the economic burden of hospitalisation for or with heart failure, by the use of ICD hospital discharge coding, may substantially underestimate the true cost [13]. The direct costs of managing heart failure hospital admissions coded in the 1st position in the UK in 1995 were calculated as *£489.7 million and in the 2nd and 3rd position a further £645.6 million accounting for about 50% of the total health care expenditure on heart failure of about 1.5 billion in 1995, rising to > *£2 billion by 2000 [13]. If this analysis is corrected only for the additional hospitalisations for heart failure that we have identified, a more accurate account of expenditure would be an additional *£182–409 million and suggests that about 2% of all health care expenditure in the UK is for the rather disorganised care for heart failure [14,15].

There was relatively good agreement between the presence of heart failure and a discharge code of heart failure in any position with coding in the 1st position being only slightly superior. Overall, miscoding was less than anticipated, compared to the findings of another study estimating numbers of heart failure patients eligible for biventricular pacing [16].

Only 28% of patients had heart failure coded in the 1st position but this increased to 70% when extended to the 2nd position. The percentage of first coding positions, relative to other coding positions, for heart failure was less than in other studies investigating patients hospitalised with heart failure [3,17]. However, one of these studies investigated incident cases or first hospitalisation with heart failure rather than chronic heart failure cases [17], which may increase first position coding for heart failure. A more likely reason though for a lower percentage of coding in first position is local coding practices; greater emphasis may have been placed on listing the underlying cause of heart failure in the first position in our centre. Whether the precipitating cause (for instance myocardial infarction or AF) or the main consequence (for instance heart failure) is recorded in the first position is likely to vary unless strictly regulated.

7.1. Limitations of the study
Assessing both systolic and diastolic ventricular function may be difficult when the underlying rhythm is AF, creating uncertainty about a diagnosis of heart failure [18–20]. However, it is likely that AF is the principal cause of heart failure in some patients and AF itself could be considered sufficient evidence of cardiac dysfunction to fulfil the ESC definition [8]. In this analysis, heart failure symptoms combined with left atrial dilatation [10], supported by evidence of ventricular hypertrophy and the absence of an alternative explanation for the patients symptoms such as respiratory disease were the main criteria used to diagnose heart failure in patients with preserved left ventricular systolic function. In those coded for heart failure the diagnosis of probable or definite heart failure with preserved left ventricular systolic function was made in 20 patients. Of these patients 19 were on diuretics, 15 had improved with heart failure treatment in the past and 14 had suffered from decompensated heart failure on admission. Only 1 out of the 20 had a normal ECG. Amongst all patients with probable or definite heart failure identified by way of screening patients with AF, only 43 out of 238 (18%) had preserved left ventricular function. Of these 30 (70%) were on diuretics, 14 (33%) had suffered from decompensation of heart failure on index admission and only 2(5%) had a normal ECG. The Euroheart Failure study [21] found preserved left ventricular systolic function to comprise 22% of men and 45% of women admitted with heart failure. The smaller proportion in this study reflects the strictness of the definition and the necessity of excluding other pathologies that could explain symptoms.

This was a retrospective case note review and information regarding admissions is dependent on the quality of note keeping and adequacy of investigations in patients admitted with breathlessness, palpitations or oedema. However most of the information needed could be acquired either from the medical or nursing notes, by scrutinising correspondence with general practitioners or a search in departmental databases to retrieve results of investigations. A prospective study would probably affect coding practice and improve diagnostic accuracy.

This study includes admissions in three winter months and therefore could have overestimated total annual admissions. However, coding data suggests only a small seasonal variation in heart failure discharges suggesting that we overestimated annual admissions by less than 100 cases [22,23].

This study also shows that morbidity associated with AF is underestimated to an even greater extent than heart failure. Only 325 of 495 patients with AF had this recorded as part of the discharge diagnosis in any diagnostic position.

	8. Conclusion

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 
Hospital discharge codes appear relatively accurate but substantially underestimate admissions for or complicated by heart failure.

	References

Top Abstract 1. Introduction 2. Participants and methods 3. Criteria for classifying... 4. Symptoms of heart... 5. Objective evidence of... 6. Results 7. Discussion 8. Conclusion References

 

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