{"id":"complement-c4","name":"Complement C4","shortName":"C4","aliases":["C4","C4 Complement","Complement C4, Serum","C4, Quantitative","Complemento C4","C4 Complement, Serum","C4 Complement Serum","C4, Serum","4th Component of Complement, Serum","Fourth Component of Complement","Complement Component 4","Complement C4, S","Complement C4 Quant","Serum C4"],"abbreviations":["C4"],"loinc":[{"code":"4498-2","primary":true}],"specimen":"serum-or-plasma","units":[{"ucum":"mg/dL","display":"mg/dL"},{"ucum":"g/L","display":"g/L"},{"ucum":"mg/L","display":"mg/L"}],"referenceRanges":[{"population":"18+","low":12,"high":38,"unit":"mg/dL","unitDisplay":"mg/dL","note":"Labcorp interval for adults over 17 (test 001834), from its pediatric reference ranges document, with no sex split. Other labs differ: ARUP prints 10–40 mg/dL for ages 18 and up, Mayo prints 14–40 mg/dL, and ABIM lists 14–48 mg/dL. Use the interval printed on your own report first.","sources":[{"title":"Pediatric Testing Reference Ranges (includes adult intervals for Labcorp tests 001776, 001784, 001792 and 001834)","url":"https://www.labcorp.com/content/dam/labcorp/drupal/178250_DX_TL_PediatricTestRef_Final.pdf","publisher":"Labcorp Diagnostics"},{"title":"Complement Component 4 (test 0050155)","url":"https://ltd.aruplab.com/Tests/Pub/0050155","publisher":"ARUP Laboratories"},{"title":"Complement C3 and C4 with Anti-C1q Antibodies, Serum (test C341Q)","url":"https://www.testcatalog.org/show/C341Q","publisher":"Mayo Clinic Laboratories (via testcatalog.org)"},{"title":"ABIM Laboratory Test Reference Ranges, January 2026","url":"https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf","publisher":"American Board of Internal Medicine","year":2026}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"A protein in the complement system, part of your immune defense. Low or high levels are read together with C3 and your symptoms.","url":"https://bloodtesttracker.com/markers/complement-c4","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}