Mixing study (1:1 mix)

A laboratory test used to distinguish factor deficiencies versus factor inhibitors such as lupus anticoagulant. The test is performed by mixing the patient's plasma with a known normal control plasma in a 1:1 ratio. If the 1:1 mixing study results in the correction of PT and/or PTT, then the patient most likely has a factor deficiency. Follow-up factor assays can be performed to further identify the deficiency. No correction mostly likely indicates the presence of a factor inhibitor (most likely an antibody). For patients on anticoagulant therapy, the test should not be performed until the anticoagulant is discontinued. In some situations, the inhibitors are time-dependent, therefore, the 1:1 mix is incubated for 2 hours at 37° C first. An example of such a time-dependent inhibitor is the Factor VIII inhibitor.