Other Coagulation Tests Hematology Review 355
TEST DISCUSSION
Mixing studies
Activated clotting
time (ACT)
Thrombin
time (TT)
Reptilase time
Fibrinogen
Factor assays
Factor XIII
screening test
Anti-Factor Xa
assay
Follow up to abnormal PT or APTT. Test is repeated on 1:1 mixture of pt plasma & normal plasma. If pt has factor defi-
ciency, time will be corrected because normal plasma supplies missing factor. If time is not corrected, an inhibitor is
present, e.g., antibody or anticoagulant.Whole blood clotting method using point-of-care analyzer. Used in cardiac care units & during cardiac surgery to
monitor heparin.Measures time required for thrombin to convert fibrinogen to fibrin. Prolonged with hypo- or dysfibrinogenemia,
heparin, FDPs.Similar to TT except uses reptilase (snake venom enzyme) instead of thrombin. Prolonged results with afibrinogenemia &
most congenital dysfibrinogenemias. Variable results with hypofibrinogenemia. Not affected by presence of heparin.Estimation of fibrinogen level by modified TT. Thrombin added to dilutions of pt plasma. Results obtained from
calibration curve prepared from testing dilutions of a fibrinogen standard. Normal: 200–400 mg/dL.% of factor activity determined by amount of correction of PT or APTT when dilutions of pt plasma are added to
factor-deficient plasma.Pt’s platelet-rich plasma mixed with CaCl 2. Clot placed in urea or monochloroacetic acid & incubated at 37°C. With XIII
deficiency, clot dissolves within 24 hr.Test to monitor therapy with low molecular weight heparin. Can also be used instead of APTT to monitor therapy with
unfractionated heparin. Pt plasma added to excess factor Xa & substrate specific for factor Xa. Heparin in sample forms
complex with AT & inhibits factor Xa. Residual factor Xa cleaves substrate to produce colored product whose intensity
is inversely proportional to concentration of heparin.