Concept: Ambulatory Care Sensitive (ACS) Conditions

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Concept Description

Last Updated: 2017-03-02

    This concept defines Ambulatory Care Sensitive (ACS) Conditions and describes how these measures are used in MCHP research.

    Billings et al. (1993) defined Ambulatory Care Sensitive (ACS) Conditions as a set of 28 medical conditions/diagnoses "for which timely and effective outpatient care can help to reduce the risks of hospitalization by either preventing the onset of an illness or condition, controlling an acute episodic illness or condition, or managing a chronic disease or condition". In an access type of model, variation in hospitalization rates is explained by differences in access to care prior to hospitalization; these differences tend to be associated with socioeconomic status. In the Billings et al. (1993) model, a set of 28 medical conditions was developed, for which a group of physicians agreed hospital use might be reduced by timely and effective outpatient care prior to the need for hospitalization; hence, the terms "avoidable" or "preventable" hospital use (Billings et al., 1996). Appropriate prior ambulatory care could:

    • prevent the onset of an illness or condition;
    • control an acute episodic illness or condition; or
    • manage a chronic disease or condition

    The programming to define ACS conditions was thoroughly checked by several MCHP employees; it was also cross-checked against the code that Billings et al. (1993) used in their 1993 paper.

    MCHP developed specific SAS code that can be used in conjunction with programming for ACS conditions. See the SAS Code links below (internal access only). This includes the following SAS (text) files:

    • ACS SAS Code and Formats - 1994 - this is the original SAS code developed by MCHP
    • ACS Comparison SAS Code - 2002 - extracts comparative information for a 3-digit analysis of diagnoses codes between Hospital Abstract data and Medical Services / Claims data.
    • ACS Rates SAS Code - ICD-9-CM and ICD-10-CA Coding - From 2013 RHA Indicators Atlas - this is the most recent SAS Code available for ACS Conditions
Comparison of 5- and 3-Digit Diagnoses Codes for Selected Ambulatory Care Sensitive (ACS) Conditions
    In Manitoba, ICD-9-CM codes are coded up to the 5-digit level for certain diagnoses/conditions in the Hospital Abstracts data, but only at the 3-digit level in the Medical Services / Physician Claims data. In Roos LL et al. (2005), they compared 3-digit ICD-9-CM codes in the abstract data from 1998 - 2000 with the diagnoses codes suggested by Billings et al. (1993,) in order to analyze the difference between the total number of codes that would be reported for ACS conditions in Manitoba data.

    The comparison found that twelve relatively common ACS conditions can be specified almost completely on the basis of the 3-digit ICD-9-CM codes. The conditions are: asthma, angina, pelvic inflammatory disease, gastroenteritis, congestive heart failure, severe ear-nose-throat (ENT) infections, epilepsy, bacterial pneumonia, tuberculosis (pulmonary and other), iron deficiency anemia in children up to 5 years of age, cellulitis, and dental conditions.
    The following table lists the twelve ACS Conditions, any exclusions that are applied to the conditions, the ICD-9-CM codes used by Billings et al. (1993) and the 3-digit codes applied in Roos LL et al. (2005).
    ACS Conditions Exclusions Codes Using Billings et al. Definitions Codes Using 3-digit Adaptations
    Asthma None 493 493
    Angina Exclude cases with a surgical procedure 411.1, 411.8, 413 411, 413
    Pelvic inflammatory disease Exclude cases with a hysterectomy procedure 614 614
    Gastroenteritis None 558.9 558
    Congestive heart failure Exclude cases with a surgical procedure 402.01, 402.11, 402.91, 428, 518.4 428, 518
    Severe ENT infections Exclude otitis media (382) cases with a myringotomy procedure 462, 463, 465, 472.1, 382 462, 463, 465, 472, 382
    Epilepsy None 345 345
    Bacterial pneumonia Exclude cases with a secondary diagnosis of sickle cell or patient age less than 2 months old 481, 482.2, 482.3, 482.9, 483, 485, 486 481, 482, 483, 485, 486
    Pulmonary/other tuberculosis None 011 011
    Iron deficiency anemia Exclude cases where patient is greater than 5 years old 280.1, 280.8, 280.9 280
    Dental conditions None 521, 522, 523, 525, 528 521, 522, 523, 525, 528
    Cellulitis Exclude cases with a surgical procedure, except incision of skin and subcutaneous tissue (86.0) when listed as only procedure 681, 682, 683, 686 681, 682, 683, 686

    See the SAS code and formats section below for the ACS Comparison SAS Code - 2002 (internal access only) used to extract this comparative information.

    The following table lists the numbers and percentage difference reported for each method for each of the twelve ACS conditions.

    ACS Conditions * N Using
    Billings et al.
    N Using
    % Increase
    Using 3-digit
    Pelvic inflammatory disease
    Congestive heart failure
    Severe ENT infections
    Bacterial pneumonia
    Pulmonary/other tuberculosis
    Iron deficiency anemia ***
    Dental conditions
    Notes to Table
    * Diagnoses are ordered according to the degree of consensus among three panels reported by Brown et al. (2001). The top five diagnoses in this table were identified by all panels as ambulatory care sensitive.

    ** Billings et al. (1993) suggest 4-digit definitions for several conditions. Some 5-digit codes were used to specify congestive heart failure.

    *** Iron deficiency anemia in children up to 5 years of age
ICD-9-CM and ICD-10-CA / CCI Codes for ACS Conditions / Diagnoses
    In Fransoo et al. (2009) and (2013), they investigated hospitalization rates for ACS conditions and reported on the findings. In both RHA Atlas deliverables, the Hospital Abstracts data was reviewed and the following ICD-9-CM and ICD-10-CA / CCI codes were used to identify 25 ACS conditions:
    1. Congenital Syphilis: ICD-9-CM code 090; ICD-10-CA code A50 (newborns only)
    2. Immunization-Related and Preventable Conditions: ICD-9-CM codes 033, 037, 045, 390, 391; ICD-10-CA codes A35, A37, A80, I00, I01 (also including hemophilus meningitis for children ages 1-5 only, ICD-9-CM code 320.0; ICD-10-CA code G00.0)
    3. Epilepsy: ICD-9-CM code 345; ICD-10-CA codes G40, G41
    4. Convulsions: ICD-9-CM code 780.3; ICD-10-CA code R56
    5. Severe ENT Infections: ICD-9-CM codes 382, 462, 463, 465, 472.1; ICD-10-CA codes H66, J02, J03, J06, J312 (cases of otitis media, ICD-9-CM code 382; ICD-10-CA code H66, with a procedure code for myringotomy with insertion of tube are excluded, ICD-9-CM procedure code 20.01; CCI code 1.DF.53.JA-TS)
    6. Pulmonary Tuberculosis: ICD-9-CM code 011; ICD-10-CA codes A15.0, A15.1, A15.2, A15.3, A15.7, A15.9, A16.0, A16.1, A16.2, A16.7, A16.9
    7. Other Tuberculosis: ICD-9-CM codes 012-018; ICD-10-CA codes A15.4, A15.5, A15.6, A15.8, A16.3, A16.4, A16.5, A16.8, A17, A18, A19
    8. Chronic Obstructive Pulmonary Disease (COPD): ICD-9-CM codes 491, 492, 494, 496; ICD-10-CA codes J41, J42, J43, J44, J47 (also included in 2005/06 are patients with a primary diagnosis of acute lower respiratory infection, ICD-10-CA codes J10.0, J11.0, J12-J16, J18, J21, J22, and a secondary diagnosis of COPD with acute lower respiratory infection, ICD-10-CA code J44)
    9. Acute Bronchitis: (only included if a secondary diagnosis of COPD is also present, diagnosis codes as above), ICD-9-CM code 466.0; ICD-10-CA code J20
    10. Bacterial Pneumonia: ICD-9-CM codes 481, 482.2, 482.3, 482.9, 483, 485, 486; ICD-10-CA codes J13, J14, J15.3, J15.4, J15.7, J15.9, J16, J18 (patients with a secondary diagnosis of sickle-cell anemia, ICD-9-CM code 282.6; ICD-10-CA codes D57.0, D57.1, D57.2, D57.8, and patients less than two months of age are excluded)
    11. Asthma: ICD-9-CM code 493; ICD-10-CA code J45
    12. Congestive Heart Failure (CHF): ICD-9-CM codes 402.01, 402.11, 402.91, 428, 518.4; ICD-10-CA codes I50, J81 (patients with certain cardiac procedures coded are excluded, ICD-9-CM procedure codes 36.01, 36.02, 36.05, 36.1, 37.5, 37.7; CCI codes 1.HB.53, 1.HB.54, 1.HB.55, 1.HD.53, 1.HD.54, 1.HD.55, 1.HZ.53, 1.HZ.55, 1.HZ.85, 1.IJ.50, 1.IJ.57.GQ, 1.IJ.76)
    13. Hypertension: ICD-9-CM codes 401.0, 401.9, 402.00, 402.10, 402.90; ICD-10-CA codes I10.0, I10.1, I11 (patients with certain cardiac procedures coded are excluded, procedure codes as in CHF)
    14. Angina: ICD-9-CM codes 411.1, 411.8, 413; ICD-10-CA codes I20, I23.82, I24.0, I24.8, I24.9 (patients with any surgical procedure coded are excluded)
    15. Cellulitis: ICD-9-CM codes 681, 682, 683, 686; ICD-10-CA codes L03, L04, L08, L44.4, L88, L92.2, L98.0, L98.3 (patients with any surgical procedure coded are excluded, except for incisions of skin and subcutaneous tissue, ICD-9-CM procedure code 86.0; CCI codes 1.AX.53.LA-QK, 1.IS.53.HN-LF, I.IS.53.LA-LF, 1.JU.53.GP-LG, 1.KR.53.LA-LF, 1.OA.53.LA-QK, 1.SY.53.LA-QK, 1.YA.35.HA-W1, 1.YA.35.HA-X4, 1.YA.52.HA, 1.YA.52.LA, 1.YA.55.DA-TP, 1.YA.55.LA-TP, 1.YA.56.LA, 1.YB.52.HA, 1.YB.52.LA, 1.YB.55.DA-TP, 1.YB.55.LA-TP, 1.YB.56.LA, 1.YF.35.HA-W1, 1.YF.35.HA-X4, 1.YF.52.HA, 1.YF.55.DA-TP, 1.YF.55.LA-TP, 1.YF.56.LA, 1.YG.52.HA, 1.YG.52.LA, 1.YG.55.DA-TP, 1.YG.55.LA-TP, 1.YG.56.LA, 1.YR.52.HA, 1.YR.52.LA, 1.YR.56.LA, 1.YS.35.HA-W1, 1.YS.35.HA-X4, 1.YS.52.HA, 1.YS.52.LA, 1.YS.55.DA.TP, 1.YS.55.LA-TP, 1.YS.56.LA, 1.YT.35.HA-W1, 1.YT.35.HA-X4, 1.YT.52.HA, 1.YT.52.LA, 1.YT.55.DA-TP, 1.YT.55.LA-TP, 1.YT.56.LA, 1.YU.52.HA, 1.YU.52.LA, 1.YU.55.DA-TP, 1.YU.55.LA-TP, 1.YU.56.LA, 1.YV.35.HA-W1, 1.YV.35.HA-X4, 1.YV.52.HA, 1.YV.52.LA, 1.YV.55.DA-TP, 1.YV.55.LA-TP, 1.YV.56.LA, 1.YW.52.HA, 1.YW.52.LA, 1.YW.55.DA-TP, 1.YW.55.LA-TP, 1.YW.56.LA, 1.YX.52.HA, 1.YX.52.HA-AV, 1.YX.52.LA, 1.YX.56.LA, 1.YZ.35.HA-W1, 1.YZ.35.HA-X4, 1.YZ.52.HA, 1.YZ.52.LA, 1.YZ.55.DA-TP, 1.YZ.55.LA-TP, 1.YZ.56.LA)
    16. Diabetes: ICD-9-CM codes 250.0, 250.1, 250.2, 250.3, 250.8, 250.9; ICD-10-CA codes E10.1, E10.6, E10.7, E10.9, E11.0, E11.1, E11.6, E11.7, E11.9, E13.0, E13.1, E13.6, E13.7, E13.9, E14.0, E14.1, E14.6, E14.7, E14.9
    17. Hypoglycemia: ICD-9-CM code 251.2; ICD-10-CA codes E16.0, E16.1, E16.2
    18. Gastroenteritis: ICD-9-CM code 558.9; ICD-10-CA codes K52.2, K52.8, K52.9
    19. Kidney/Urinary Infections: ICD-9-CM codes 590, 599.0, 599.9; ICD-10-CA codes N10, N11, N12, N13.6, N15.1, N15.8, N15.9, N16.0-N16.5, N28.83-N28.85, N36.9, N39.0, N39.9
    20. Dehydration/Volume Depletion: ICD-9-CM code 276.5; ICD-10-CA code E86
    21. Iron Deficiency Anemia: ICD-9-CM codes 280.1, 280.8, 280.9; ICD-10-CA codes D50.1, D50.8, D50.9 (patients age 0-5 only)
    22. Nutritional Deficiencies: ICD-9-CM codes 260, 261, 262, 268.0, 268.1; ICD-10-CA codes E40-E43, E55.0, E64.3
    23. Failure to Thrive: ICD-9-CM code 783.4; ICD-10-CA code R62 (patients less than one year of age only)
    24. Pelvic Inflammatory Disease: ICD-9-CM code 614; ICD-10-CA codes N70, N73, N99.4 (female patients only, patients with a hysterectomy procedure coded are excluded, ICD-9-CM procedure codes 68.3-68.8; CCI codes 1.RM.87, 1.RM.89, 1.RM.91, 5.CA.89.CK, 5.CA.89.DA, 5.CA.89.GB, 5.CA.89.WJ, 5.CA.89.WK)
    25. Dental Conditions: ICD-9-CM codes 521, 522, 523, 525, 528; ICD-10-CA codes K02-K06, K08, K09.8, K09.9, K12, K13

    • For all ACS conditions above (except congenital syphilis), the ACS condition must be coded as the most responsible diagnosis and the patient, unless otherwise noted, must be between the ages of 0-74.
    • Low rates of hospitalizations for ACS conditions can be used as indicators of access to good quality primary care.
    • This list of 25 conditions is an adaptation of the original work by Billings et al. (1993). In this list, convulsions are combined into one category, regardless of age; all types of diabetes are combined into one category; and a category identifying acute bronchitis has been added.
MCHP Research Investigating Hospitalizations for Ambulatory Care Sensitive (ACS) Conditions
    For more information on how MCHP has investigated Hospitalizations for Ambulatory Care Sensitive (ACS) Conditions, please see:

    • In the article Physician visits, hospitalizations, and socioeconomic status: ambulatory care sensitive conditions in a Canadian setting by Roos et al. (2005), they investigate whether rates of physician visits for 12 ACS conditions, definable using 3-digit ICD-9-CM codes that allow cross-sectional and longitudinal comparison of ambulatory visits and hospitalizations, are lower for people of low-socioeconomic status than of high socioeconomic status. In this research, they could not include emergency department and outpatient visits because these types of services are not part of the standard Manitoba hospital abstract data sets. "A relatively small number of such visits (based in the Winnipeg teaching hospitals) are captured as ambulatory visits. An earlier, more labor-intensive analysis using 1 year of Winnipeg data found 4.9 percent of ambulatory care to be provided in emergency departments. (Mustard et al. 1998)".

    • In Fransoo et al. (2009), they compare hospitalization rates for 17 ACS conditions for two time periods (2000/01 and 2005/06) by RHA, RHA Districts and Winnipeg Neighbourhood Clusters. See section 7.13 Hospitalization Rates for Ambulatory Care Sensitive (ACS) Conditions for more information.

    • In Fransoo et al. (2013), they compare hospitalization rates for 17 ACS conditions for two time periods (2006/07 and 2011/12) by RHA (for both current (5) and former (11) RHAs), RHA Districts and Winnipeg Neighbourhood Clusters. See section 7.11 Hospitalization Rates for Ambulatory Care Sensitive (ACS) Conditions for more information.

    • In Katz et al. (2014, they investigate hospitalizations for a select group of ambulatory care sensitive (ACS) conditions that include chronic obstructive pulmonary disease, congestive heart failure, diabetes, and asthma as part of the evaluation of the implementation of Physician Integrated Network (PIN) clinics. See the section titled Hospitalizations for Ambulatory Care Sensitive Conditions for more information.

Related concepts 

Related terms 


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  • Health Measures
  • health status indicators
  • hospitalization

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