Lower extremity ulcers (LEU) and amputations (LEA) as well as other foot complications are a serious preventable problem among patients with diabetes. To establish a hospital-based surveillance system for foot complications and to initiate quality improvement efforts to prevent future complications, we used a case definition developed by Harrington et al. (1). The authors developed this definition as part of a cost analysis study of foot complications among Medicare beneficiaries. The case definition utilizes ICD-9-CM diagnosis codes and Current Procedural Terminology, version 4 (CPT-4), procedural codes to identify patients with diabetes having a LEU, LEA, or other foot complications. First, patients with diabetes were identified based on hospitalization diagnoses. Then, the subgroup of patients with ICD-9-CM diagnoses of CPT-4 procedure codes for possible foot complications were identified. The ICD-9-CM diagnoses included LEU; carbuncle or furuncle of the foot; cellulitus of abscess of the toe or foot; gangrene; infectious myositis; unspecified myalgia or myositis; osteomyelitis; amputation or resection of the foot, ankle, leg, or knee and above; and late amputation stump complication. The CPT-4 procedures included simple repair of a superficial wound; debridement; lower extremity radiographic techniques; angioscopy; arteriography; angiography; lower extremity CAT or MRI scanning; incision or excision of the foot; Unna’s boot application; and amputation or resection of the foot, ankle, leg, or knee and above. The validity of this case definition, to our knowledge, has not been established. This report describes the adaptation of this case definition using hospitalization discharge data and an evaluation of its validity.
Patients hospitalized with diabetes (ICD-9-CM codes 250, 250.0–250.9, 251.0, and 362.01–362.02) at two hospitals in Missoula, Montana (the Saint Patrick Hospital and Health Sciences Center and the Community Medical Center), in 1999–2000 were identified. The subset of patients with potential foot complications based on diagnosis and procedure codes was then identified using the same definition as Harrington et al. We added ICD-9-CM codes for Charcot disease (ICD-9-CM 94.0 and 713.5) and revascularization or bypass surgery (ICD-9-CM 38.08, 38.09, 38.48, and 38.49) as part of the case definition to increase the sensitivity. The medical records of hospitalized patients with diabetes and foot complications were then reviewed to confirm that these cases were correctly classified. A systematic sample (4%) of medical records of patients with diabetes but without foot complications listed was also reviewed to confirm the absence of obvious foot problems.
A total of 3,596 hospitalizations were identified, and 157 (4.4%) had ≥1 foot problem coded as a discharge diagnosis or procedure code. Of these hospitalizations, 58% were men, and the mean age was 65 years. The majority of the discharge diagnoses were LEU (42%), LEA (36%), and cellulitus or abscess of the toe or foot (26%). Fewer discharges listed diagnoses such as LEA complication (8%), revascularization (6%), Charcot disease (5%), gangrene (4%), and infectious myositis (2%). None of the patients had discharge diagnoses for other local infections of the skin and subcutaneous tissue or for a carbuncle or furuncle of the toe or foot. Of the 157 hospitalizations for foot problems, 137 (87%) were confirmed to have ≥1 foot complication based on the medical record review, 10 (6%) had no foot complication listed, and 10 (6%) records were not available for review. Of the 10 cases with no confirmed foot complication, 4 had a history of foot complications but no current problem, 2 had ulcers on other regions of the body, 1 had a femoral bypass with no foot complication, 1 had sepsis not related to the foot, and 1 had a lower extremity clot with no other foot complications. Of the medical records of patients with diabetes but with no foot complications included in the diagnoses or procedural codes, 2 of 131 (1.5%) had a foot problem documented in the medical record (both foot ulcers). Overall, the values for sensitivity, specificity, predictive value positive, and predictive value negative of the adapted case definition were 0.99, 0.93, 0.93, and 0.98, respectively.
Our findings suggest that the methods developed by Harrington et al. as well as our adapted case definition are valid in terms of accuracy and reliability. The incorporation of diagnosis codes for Charcot disease was useful in that this condition was present among patients hospitalized with diabetes and foot complications. The incorporation of revascularization procedure codes as part of the case definition did not increase the number of false-positive cases. Overall, these case definitions can be useful not only for cost analysis studies as conducted by Harrington et al., but also for hospital-based surveillance for foot complications to initiate quality improvement efforts to prevent future foot complications.
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This project was supported through a cooperative agreement (U32/CCU815663-04) with the Centers for Disease Control and Prevention (CDC), Division of Diabetes Translation. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the CDC.
We thank Jim Joyner and Kate Jackson, PhD, for their work with the hospital discharge data, the medical records departments from both hospitals, and Crystal Nachtsheim and Kirsten Kammerzell for their assistance with the medical record review.
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Address correspondence to Todd S. Harwell, MPH, Montana Department of Public Health and Human Services, Cogswell Building, C-317, P.O. Box 202951, Helena, Montana 59620-2951. E-mail: [email protected].
N.E. has received honoraria for educational lectures from Pfizer, Glaxo SmithKline, and Merk.
