An assessment of C1 inhibitor (C1-INH) functional assay ordering patterns

Abstract

RATIONALE: The appropriate screening test for C1-INH deficiency is a C4 level. C1-INH level and functional assay confirm and classify the diagnosis. We assessed ordering patterns of C1-INH functional assay to determine the proportion obtained without a history consistent with C1-INH deficiency.METHODS: We performed a retrospective chart review of all C1-INH functional assays from 1/1/2003-6/30/2004. We defined C1-INH ordering as appropriate for patients with histories suggestive of C1-INH deficiency.RESULTS: We reviewed 126 charts; 30 men (24%), 66 women (52%), 19 girls (15%), and 11 boys (9%). Of those who had C1-INH functional assay, 91 (72%) also had C1-INH and C4 level, 7 (6%) had C1-INH, and 15 (12%) had functional assay alone. These were all normal in 111 (88%) patients. Of these 111, 31 (28%) had symptoms suspicious for C1-INH deficiency. Eighty (63%) had urticaria, musculo-rheumatic complaints, chronic abdominal pain, or other symptoms. Fifteen of the 126 (12%) had abnormal RESULTS: 9 low C4 and normal C1-INH and functional assays (1 had previously diagnosed C1-INH deficiency); 6 had low C1-INH and/or functional assay (of these, only 1 was a new diagnosis).CONCLUSIONS: Our findings demonstrate that most (63%) C1-INH functional assays are obtained in patients whose presentation is not suggestive for C1-INH deficiency. These data provide support for an educational intervention to encourage more cost-effective ordering of these tests. RATIONALE: The appropriate screening test for C1-INH deficiency is a C4 level. C1-INH level and functional assay confirm and classify the diagnosis. We assessed ordering patterns of C1-INH functional assay to determine the proportion obtained without a history consistent with C1-INH deficiency. METHODS: We performed a retrospective chart review of all C1-INH functional assays from 1/1/2003-6/30/2004. We defined C1-INH ordering as appropriate for patients with histories suggestive of C1-INH deficiency. RESULTS: We reviewed 126 charts; 30 men (24%), 66 women (52%), 19 girls (15%), and 11 boys (9%). Of those who had C1-INH functional assay, 91 (72%) also had C1-INH and C4 level, 7 (6%) had C1-INH, and 15 (12%) had functional assay alone. These were all normal in 111 (88%) patients. Of these 111, 31 (28%) had symptoms suspicious for C1-INH deficiency. Eighty (63%) had urticaria, musculo-rheumatic complaints, chronic abdominal pain, or other symptoms. Fifteen of the 126 (12%) had abnormal RESULTS: 9 low C4 and normal C1-INH and functional assays (1 had previously diagnosed C1-INH deficiency); 6 had low C1-INH and/or functional assay (of these, only 1 was a new diagnosis). CONCLUSIONS: Our findings demonstrate that most (63%) C1-INH functional assays are obtained in patients whose presentation is not suggestive for C1-INH deficiency. These data provide support for an educational intervention to encourage more cost-effective ordering of these tests.