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Immunology Laboratory

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C1 Inhibitor (levels and functional)

Also known as: C1EQ; C1 Esterase Inhibitor

C1 esterase inhibitor deficiency is the most common complement deficiency (antigenic or functional) and is transmitted as an autosomal dominant disorder resulting in hereditary angioneurotic oedema. Acquired C1 inhibitor deficiency may occur with B-cell lymphomas and some autoimmune diseases. Samples collected during an acute attack of angioedema due to C1 inhibitor deficiency are characterised by a low C4. Conversely, a normal C4 level virtually excludes all forms of C1 inhibitor deficiency.

Specimen requirements

Functional activity: 5ml EDTA

Serum levels: 1ml serum


Price on application

Laboratory turnaround time

21 days

Laboratory method

  • Functional Assay
  • Quantitaive Assay: RID

Reference range/units

  • Quantitatively: 15 - 35 mg/dl
  • Functional activity: 70 - 130%

Associated tests

Sample stability


8 days (must be stored at -80ºC)


6 hours (must be stored at -80ºC)

Shipping and storage

Samples need to reach the Laboratory within 6 hours of venepuncture.

Further information and contact details

For further information, email

Last reviewed:12 September 2022