A new capillary tube agglutination-inhibition test for the detection of circulating immune complexes containing...

The C1q agglutination-inhibition test (C1q-AIT) is a sensitive assay, capable of detecting circulating immune complexes (CIC) containing as little as 40 ng C1q. This non-isotopic test can be easily performed in 4 h from the receipt of the serum sample (including the isolation of CIC by PEG 6000 percipitation). The reagents are stable for at least 6 months under normal refrigeration. Because a carefully standardized C1q- anti-C1q reaction is used, CIC can be semi-quantitated by a routine titration procedure. Sera from patients with diseases reported to be associated with CIC gave significantly high test results, while diseases not normally associated with CIC (e.g. OA, gout, allergy) gave low frequencies of positive results. The C1q-AIT for CIC containing endogenously bound C1q was shown to be equivalent to and more sensitive than the [125I]C1q-BA for CIC containing exogenously bound C1q.