Are we underestimating diabetes-related lower-extremity amputation rates? Results and benefits of the first prospective study.

OBJECTIVE: The objective of this study was to accurately determine the incidence of lower-extremity amputation using prospective data collection and to compare the results with those obtained by retrospective methods. RESEARCH DESIGN AND METHODS: The study was carried out over a 3-year period in a large district general hospital covering a clearly defined and relatively static population. All diabetic inpatients with foot problems were identified and followed-up until discharge or death. The demographic and admission details, medical history, investigations, procedures, and history and etiology of the foot lesion were collected twice weekly by a specialist nurse and podiatrist from all relevant wards. Thus, all subjects who underwent amputation could be identified. For comparison, retrospective data were collected from the hospital coding activities database, operating theater log books, anesthetic database, and limb-fitting records.
RESULTS: The total population of the region in 2000 was 337,859, of which 9,183 were known to have diabetes. The total number of amputations during the 3-year survey period was 79, of which 45 were major and 34 minor. In our local population, the mean incidence during the survey period (1997-2000) equates to 7.8/100,000 general population and 2.85/1,000 diabetic population for all amputations, 4.5/100,000 general population and 1.62/1,000 diabetic population for major amputations, and 3.3/100,000 general population and 1.23/1,000 diabetic population for minor amputations. The prospective survey detected all lower-extremity amputations identified by the various retrospective methods; however, for the reverse, this was not the case. All of the retrospective methods, including the most commonly used (ICD-9 and OPCS-4 coding), failed to detect all of the cases revealed by the prospective survey (error rate ranging from 4.2 to 90.6%), and between 4.5 and 17.4% of amputations were misclassified.
CONCLUSIONS: This study demonstrates the advantages of prospective data collection as a means of determining the incidence of lower-extremity amputations and highlights the limitations of retrospective data collection methods, which underestimate the incidence. In particular, the operating theater records, which have been the gold standard for many surveys, were found to be unreliable. Moreover, we have shown a 47% reduction in the major amputations during the survey period. Thus, we recommend that a prospective audit be incorporated into the activities of the specialist foot care team as a means of assessing and improving clinical care.