Complement C3 optimal range and reference range

Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026

Sera's bands for Complement C3:

  • Optimal 90 – 175 mg/dL (0.9 – 1.75 g/L); sufficient 75 – 175 mg/dL (0.75 – 1.75 g/L); out of range below 75 or above 175 mg/dL.

Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.

All units

UnitOptimalSufficientOut of range
mg/dL90 – 17575 – 175below 75 or above 175
g/L0.9 – 1.750.75 – 1.75below 0.75 or above 1.75

What the evidence says

Read for what it falls to. A low C3 with a low C4 means complement is being consumed, which in lupus tracks disease activity and renal involvement. C3 is also an acute-phase reactant, so concurrent inflammation can lift it and mask consumption, which is the reason the pair is always ordered together. The band is the Mayo Clinic Laboratories reference interval, 75 to 175 mg/dL (0.75 to 1.75 g/L). Laboratory intervals differ, with lower limits from 65 to 90 mg/dL and upper limits from 167 to 190, so the interval printed on the report takes precedence. The narrower optimal band is a functional target; no published evidence supports it.

Sources

  • Complement C3, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceReference interval 75 to 175 mg/dL; a fall into the abnormal range is consistent with disease activation in lupus. This is the proposed sufficient band (0.75 to 1.75 g/L).
  • Complement C3 — Labcorp, 2026 · Laboratory / reference-interval sourceReference interval 82 to 167 mg/dL for men and women beyond the first month of life. Close to Sera's current lower edge of 80, and well short of 200 at the top.
  • Complement (C3, C4 Levels) — Gloucestershire Hospitals NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceUK laboratory interval for C3 of 0.90 to 1.80 g/L (updated January 2026). This equals Sera's current optimal band of 90 to 180 mg/dL, showing that band is a reference interval and not a tighter target.

What Complement C3 measures

The central protein of the complement cascade, consumed when immune complexes activate it.

Read for what it falls to, not what it rises to. A low C3 with a low C4 means complement is being consumed, which in lupus tracks disease activity and particularly renal involvement. C3 is also an acute-phase reactant, so active inflammation can push it up and mask consumption — which is why the pair is ordered together.

Related autoimmune markers

See Complement C3 in the full list of biomarker ranges

About the author

Alina Radu is the founder of Sera and a software engineer. The idea started with her own Hashimoto's tests, scattered across years without the big picture. She is not a clinician: these ranges are compiled from the published sources linked on each page, with every source named. Alina Radu on LinkedIn

This page is a reference for practitioners, not medical advice. Sera's bands are practitioner targets for structured review, not diagnostic thresholds, and Sera does not diagnose or recommend treatment. Read a result alongside the interval printed by the issuing laboratory and the client's history and symptoms. Range set: Sera Production, version 1.0, last reviewed November 9, 2026.