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C4 Complement Factor Unit Converter
Complement Component 4 (C4) is a protein involved in the classical and lectin pathways of the complement system. Synthesized in the liver, it plays a crucial role in pathogen recognition and the formation of the C3 convertase enzyme, which amplifies the immune response.
Like C3, C4 behaves as an acute-phase reactant, rising during inflammation. However, its most significant clinical value lies in the diagnosis and monitoring of immune complex diseases. Low levels of C4 are strongly associated with active Systemic Lupus Erythematosus (SLE), cryoglobulinemia, and hereditary angioedema (due to C1 esterase inhibitor deficiency). Consistently low C4 with normal C3 may suggest a null allele (genetic deficiency) rather than consumption.[Image of acute phase protein response] This converter allows precise switching between the standard SI unit (g/L) and the conventional mass unit (mg/dL).
SI Units
RecommendedGrams per liter (Standard International).
Conventional Units
*Molar conversion based on C4 MW ≈ 205 kDa.
Clinical Context
Reference Ranges: Serum C4 levels in healthy adults typically range from 10 – 40 mg/dL (0.1 – 0.4 g/L), significantly lower than C3 levels.
Hypocomplementemia: Depressed C4 is a sensitive marker for classical pathway activation (e.g., in SLE vasculitis). In Hereditary Angioedema, C4 is chronically low even between attacks, making it an excellent screening test. The conversion factor is simple: 1 g/L = 100 mg/dL.
Clinical References
How to Use This Calculator
Follow these steps to get accurate clinical conversions instantly.
Enter Values
Input your laboratory results into the corresponding unit field (e.g., mg/dL). You can use either dot or comma decimals.
Automatic Conversion
The calculator works in real-time. As you type in one field, all other units (like g/L) are instantly updated.
Verify Units
Check the SI Units section. g/L is the standard SI unit, while mg/dL is common in the US.
Reset
Use the Clear button to reset all fields before starting a new calculation.
Frequently Asked Questions & Tips
Comparing both helps distinguish activation pathways. Low C4 usually points to the Classical pathway (immune complexes).
Yes. 1 g/L is exactly equal to 1 mg/mL.