Hospitalizations for Acute Exacerbations of Chronic Obstructive Pulmonary Disease: How You Count Matters

Figures & data

Table 1.  ICD-9-CM codes used in algorithms to identify AE-COPD

ICD-9-CM code	Description
490	Bronchitis, not specified as acute or chronic
491.0	Simple chronic bronchitis
491.1	Mucopurulent chronic bronchitis
491.20	Obstructive chronic bronchitis without exacerbation
491.21	Obstructive chronic bronchitis with acute exacerbation
491.22	Obstructive chronic bronchitis with acute bronchitis
491.8	Other chronic bronchitis
491.9	Unspecified chronic bronchitis
492.0	Emphysematous bleb
492.8	Other emphysema
493.22	Chronic obstructive asthma with acute exacerbation
494.0	Bronchiectasis without acute exacerbation
494.1	Bronchiectasis with acute exacerbation
495.0	Farmers’ lung
495.1	Bagassosis
495.2	Bird-fanciers’ lung
495.3	Suberosis
495.4	Malt workers’ lung
495.5	Mushroom workers’ lung
495.6	Maple bark-strippers’ lung
495.7	Ventilation” pneumonitis
495.8	Other specified allergic alveolitis and pneumonitis
495.9	Unspecified allergic alveolitis and pneumonitis
496	Chronic airway obstruction, not elsewhere classified
518.81	Acute respiratory failure
518.82	Other pulmonary insufficiency not elsewhere classified
518.84	Acute and chronic respiratory failure

The table above includes all ICD-9-CM codes that have been used in five published algorithms employed to identify patients hospitalized for acute exacerbations of COPD (AE-COPD).

Abbreviations: ICD-9-CM, International Classification of Disease, Ninth Edition, Clinical Modification.

Table 2.  Different ICD-9-CM algorithms used to identify hospitalizations for AE-COPD

Algorithm	Age	Primary ICD-9-CM Diagnosis	Secondary ICD-9-CM Diagnosis
1 [Patil] ^(12)	≥40 yrs	491.21	None
2 [HEDIS] ^(14)	≥40 yrs	491.x, 492.x, or 496	None
3 [Holguin] ^(10)	≥25 yrs	490, 491.x,492.x, or 496	None
4 [NHLBI] ^(7)	All yrs	490, 491.x, 492.x, 494.x, 495.x, or 496	None
5 [Lee] ^(17)	≥40 yrs	491.0, 491.1, 491.21, 491.22, 491.8, 491.9, 492.0, 492.8, 493.22, or 496**	None
		OR
		518.81, 518.82 or 518.84AND	491.0, 491.1, 491.21, 491.22, 491.8, 491.9, 492.0, 492.8, 493.22, or 496**

Abbreviations: ICD-9-CM, International Classification of Disease, Ninth Edition, Clinical Modification; AE-COPD, acute exacerbation of chronic obstructive pulmonary disease.

*Secondary ICD-9-CM Diagnosis may be in any position after the first.

**Excluded if 491.20 (obstructive chronic bronchitis without exacerbation) in any diagnostic field.

ICD-9.x represents all possible ICD-9-CM sub-codes following the initial 3 digit ICD-9 code.

Table 3.  Hospitalizations, patient characteristics, and outcomes in 2006

	Algorithm 1 [Patil]	Algorithm 2 [HEDIS]	Algorithm 3 [Holguin]	Algorithm 4 [NHLBI]	Algorithm 5 [Lee]
Number (99% CI) Patient Characteristics	421,000 (395,000 – 447,000)	557,000 (524,000–591,000)	582,000 (547,000 – 617,000)	599,000 (563,000 – 634,000)	870,000 (817,000–922,000)
Age, yrs Mean (99% CI)	69.4 (69.1, 69.7)	69.5 (69.2, 69.8)	69.1 (68.8, 69.4)	68.5 (68.1, 68.9)	68.8 (68.5,69.1)
< 40 years,%	0.0	0.0	1.1	2.2	0.0
Female,% (99% CI)	55 (55, 56)	56 (55,56)	56 (55, 56)	56 (55, 57)	57 (57, 58)
Charlson Index,%
1	42	43	43	44	39
2	30	30	30	30	30
3	16	15	15	15	16
>4	12	12	12	12	14
Outcomes
Hospital days,
Median per hospitalization (IQR)	4 (2,6)	4 (2,6)	4 (2,6)	4 (2,6)	4 (3,7)
Total for all hospitalizations x 1 million (99% CI)	2.0 (1.9,2.1)	2.7 (2.5, 2.8)	2.7 (2.6, 2.9)	2.9 (2.7, 3.0)	5.1 (4.8, 5.4)
Hospital charges, $
Median per hospitalization x 1,000 (IQR)	12.6 (7.6,21.7)	12.7 (7.7,21.8)	12.5 (7.6,21.5)	12.6 (7.6,21.8)	15.2 (8.7, 29.2)
Total for all Hospitalizations x 1 billion (99% CI)	8.0 (7.4, 8.7)	10.7 (9.8,11.6)	11.1 (10.1, 12.0)	11.5 (10.6, 12.5)	23.8 (21.8,25.8)
Mechanical ventilation,% (99% CI)	5.2 (4.7, 5.7)	4.7 (4.3, 5.2)	4.6 (4.2, 5.0)	4.6 (4.2, 5.0)	16.5 (15.8, 17.3)
In-hospital mortality,% (99% CI)	2.1 (1.9,2.2)	2.1 (2.0, 2.3)	2.0 (1.9,2.2)	2.0 (1.9,2.2)	5.1 (4.8, 5.3)

Abbreviations: CI, confidence interval; IQR, Inter-quartile range (interval of the 25^th and 75^th percentile); yrs, years.

Percentages may not sum to 100% due to rounding.

Missing values less than 1% for all variables.

Total hospital days is the sum of all hospital days for each algorithm in 2006.

Total hospital charges is the sum of all hospital charges for each algorithm in 2006.

Figure 1.  Prevalence of selected comorbidities* across ICD-9-CM algorithms for AE-COPD.

Figure 2.  Trends in the number of hospitalizations, total hospital days, and total charges for AE-COPD, 2000-2006

Figure 3.  Trends in mechanical ventilation use and in-hospital mortality for AE-COPD, 2000-2006