EFFECT OF TIME, TEMPERATURE AND ADDITIVES ON A FUNCTIONAL ASSAY OF C1INHIBITOR

There are different recommendations for the handling of blood samples for analyses of the kallikrein-kinin or complement system, respectivel y. C1 inhibitor (C1-INH) takes a crucial part in both systems. In orde r to establish recommendations for blood specimen collection and trans port for making the diagnosis of hereditary angioedema (HAE), the effe ct of time, temperature and different additives on C1-INH function and antigen was determined. We used blood samples from normals and patien ts suffering from HAE type I. Plasma containing EDTA, heparin, sodium citrate or polybrene-EDTA, and serum were assayed after incubations at 4 degrees C or 37 degrees C for 6 or 24 h. In addition, pooled serum was incubated for up to 5 days at room temperature. A modest decrease in C1-INH function was observed as an effect of storage-time in sample s from normals (p = 0.039) and a substantial decrease was seen for the HAE patients (p = 0.0002). No significant effect of temperature (4 de grees C or 37 degrees C) was found. Clotting did not reduce C1-INH act ivity. Plasma containing heparin or polybrene interfered with the func tional assay, yielding falsely high and low values, respectively. C1-I NH functional assay performed within 24 h in serum, EDTA-treated or ci trated plasma discriminated well between HAE patients and normals. Thi s was also the case for serum kept at room temperature for up to 5 day s, although a modest fall in C1-INH function was seen in the incubatio n period. For practical purposes we recommend serum as the sample of c hoice, preferably received within 48 h.