Screening for activated protein C resistance before oral contraceptive treatment: a pilot study

Health technology Laboratory screening for congenital thrombophilic alterations in women who wished to start oral contraceptive (OC) treatment. At the first screening, the following tests were carried out on blood taken from the subjects. (1) Activated protein C resistance (APCR), using the in-house clotting method proposed by de Ronde and Bertina. The inter-assay coefficient of variation (CV) was 6.1% for normal, and 5.2% for abnormal samples. The cutoff value for abnormal cases was set at less than 0.75 of a normalised ratio. (2) Protein C activity (PC), by means of a commercial chromogenic method using Protac activation. The inter-assay CV of the method was 3.7% for normal and 5.2% for abnormal samples. Values below 62% were considered to be abnormal. (3) Protein S activity (PS), by a commercial clotting method. The inter-assay CV was 3.9% for normal, and 5.4% for abnormal samples. Values below 62% were considered as abnormal. (4) Antithrombin III activity (ATIII), using a commercial chromogenic method. The interassay CV was 2.6% for normal and 4.1% for abnormal samples. Abnormal values were considered to be those below 75%. Women with abnormal or borderline results at first screening were advised to have a second blood sample, to repeat the altered test and perform the corresponding immunologic assay or DNA analysis for factor V Leiden mutation in cases with altered APCR. For all the tests, an internal quality control was routinely performed. External quality assessment was also carried out for antithrombin III, protein C activity and activated protein C resistance.