A C1 esterase test is a blood test that measures the level and function of C1 esterase inhibitor (C1‑INH), a protein that regulates the complement system. It’s used to diagnose hereditary or acquired angioedema and unexplained recurrent swelling. The panel often includes C4 levels; low C1‑INH (quantity or function) with low C4 supports C1‑INH deficiency and guides diagnosis and monitoring.

C1 in a blood test usually refers to complement component 1 (C1) or its esterase inhibitor (C1‑INH), part of the classical complement immune pathway. C1 proteins trigger complement activation. Low C1‑INH level or function suggests hereditary or acquired angioedema; abnormal C1q/C1r/C1s patterns can indicate autoimmune or inflammatory disease. Results require clinical correlation and specialist interpretation.

Pricing varies widely by brand, dose and country. In the US, list prices are typically in the low‑thousands to over $10,000 per dose; in the UK the NHS supplies it free to eligible patients though hospital acquisition costs are often several thousand pounds; in India retail vial prices commonly range from roughly ₹20,000–₹80,000. Insurance or national health services usually cover most or all of the cost.

Normal C1 esterase inhibitor (C1‑INH) values: antigenic level about 21–39 mg/dL (0.21–0.39 g/L). Functional activity is typically reported as roughly 70–130% of normal. Markedly reduced antigenic level or function (commonly <50–70%) suggests C1‑INH deficiency and warrants further evaluation. Reference ranges can vary slightly by laboratory and assay.

Yes. Emotional or physical stress can trigger symptoms in people with C1 esterase inhibitor deficiency (hereditary angioedema). Stress may provoke bradykinin-mediated swelling attacks, as can infections, trauma, hormonal changes, and some medications (e.g., ACE inhibitors). Management includes avoiding triggers, stress reduction, and prescribed prophylactic or on‑demand treatments; seek urgent care for airway or severe swelling.

C1 esterase inhibitor deficiency causes recurrent, non‑itchy angioedema—sudden, painful swelling of the face, lips, tongue, throat, extremities or genitals. Abdominal attacks produce severe cramping, nausea, vomiting and diarrhea. Laryngeal swelling can cause hoarseness, stridor and life‑threatening airway obstruction. Attacks often begin in childhood/adolescence and may be triggered by stress, trauma or medical/dental procedures.