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Complement C4

Abbreviation: C4

Panel: Inflammation & Immune Markers · All inflammation tests

Typical adult reference range

Conventional units10–40 mg/dL
SI units0.10–0.40 g/L

Ranges vary between laboratories and methods — compare your result with the range printed on your own report.

What a high or low result can mean

High complement c4: high values can be seen as an acute-phase response to inflammation.

Low complement c4: low values may occur in active lupus, hereditary angioedema, and inherited deficiency.

These are associations, not a diagnosis: the same result can have several causes, and your clinician interprets it with the rest of your results and history.

◆ Kidney note

This test is closely tied to kidney health, and it is one a kidney specialist (nephrologist) watches closely. On this site, kidney-related results are a special focus: see the kidney and dialysis medicines in our Drug Guide and the kidney condition hubs for the wider picture.

Related tests — Inflammation & Immune Markers

Anti-Cyclic Citrullinated Peptide AntibodiesAntinuclear AntibodiesC-Reactive ProteinComplement C3Erythrocyte Sedimentation RateInterleukin-6ProcalcitoninRheumatoid Factor
Please note: Reference ranges vary between laboratories, and between the methods and instruments they use — the range printed on your own report is the one your result should be compared with. A result outside the range is not by itself a diagnosis, and a result inside it does not rule out illness. These pages are an educational summary, not medical advice: always discuss your results with the clinician who ordered them, who can interpret them in the context of your health and history.