Use of purified dermatan sulfate for heparin cofactor II (HC II) assay

HC II functional assays are generally preferred with respect to immunochemical assays. Nevertheless functional assays can be biased by the antithrombin III (AT III)-heparin complex activity; in fact trace amounts of heparin generally contaminate dermatan sulfate (DS) commercial preparations used as HC II reaction activators. We have employed a purified DS preparation showing these features: DS concentration 94.4%, chondroitin sulfate 5.6%, M.W. 21.4 kDa. The absence of any interference due to AT III-heparin complexes was verified in a kinetic HC II assay of some human plasma pools. The immunological inhibition of AT III by anti-AT III caused a minimal decrease (6-8%) of the reaction slope, attributable to AT III activity. Progressive increase of heparin concentration in the assay was effective only starting from 30 U/ml (the assay was carried out in the presence of polybrene to prevent any AT III activation). The reference interval (mean +/- SD) obtained from 157 normal subjects was 100.8 +/- 20.2%; there was a good correlation with immunoreactive HC II. The purified DS we have used seems suitable for routinary assays of HC II where a minimal interference due to AT III-heparin is required.