TABLE 2.

Commonly Used Anticoagulation Monitoring Assays and Factors Associated With Variability in Results

Influences on Coagulation Monitoring	Activated Clotting Time	Anti-Factor Xaa	aPTT When monitoring UFH	aPTT When Monitoring Bivalirudin	Thromboelastogram R-time or ROTEM INTEM Clotting Time	Thromboelastogram Maximum Amplitude or ROTEM INTEM Maximum Clot Firmness	Prothrombin Time/International Normalized Ratio When Monitoring Bivalirudin	Dilute Thrombin Time When Monitoring Bivalirudin
Sample factors
Heparin contamination	↑	↑	↑	↑	↑	↔/↓	↔/↑	↑
Dilution	↑	↓	↑	↑	↑	↔/↓	↑	↑
Under/over-filled sample tubes	Sample must be redrawn because results will be uninterpretable
Delay in sample analysis (beyond 2 hr)	Sample must be redrawn because results will be uninterpretable (optimal time to sampling for bivalirudin is unknown. Some current protocols restrict to 1 hr)
Gross hemolysis due to sampling	Sample must be redrawn because results will be uninterpretable
Patient factors
Hypothermia	↑	↔a	↔a	↔a	↔a	↔a	↔a	↔a
Elevated levels of inflammatory markers including: fibrinogen and factor VIII	↓	↔	↓	↓	↓	↔/↑	↔	↓
Increased heparin binding proteins in the presence of systemic inflammation, infection, malignancies	↓	↓	↓	↔	↓	↔/↑	↔	↔
Thrombocytopenia (generally < 50 × 109)	↑	↔	↔	↔	↔/↑	↓	↔	↔
Antithrombin deficiency	↓	↓b	↓		↓	↔
Consumptive coagulopathy (i.e., disseminated intravascular coagulation)	↑	↔/↓b	↑		↑	↓
Hepatic dysfunction (decreased coagulation factor production)	↑	↔/↓b	↑		↑	↓
Procoagulant factor deficiency(s)	↑	↔	↑	↑	↑	↔/↓	↑	↔
Presence of a lupus anticoagulant	↑	↔	↑	↑	↑	↔	↔	↔
Assay factors
Elevated triglyceride level	↔	↓c	↔/↑c	↔/↑c	↔	↔	↔/↑c	↔
Elevated total bilirubin level	↔	↓c	↔/↑c	↔/↑c	↔	↔	↔/↑c	↔
Elevated plasma-free hemoglobin	↔	↓c	↔/↑c	↔/↑c	↔	↔	↔/↑c	↔
Drug factors
Loss of linearity outside specific dose ranges	Low dose	N/A	Very high dose	High dose	Low and high dose	N/A	Therapeutic range	N/A
Impaired renal function (decreased UFH or bivalirudin elimination)	↑	↑	↑	↑	↑	↔/↓	↑	↑

aPTT = activated partial thromboplastin time, INTEM = intrinsically activated thromboelastometry, N/A = not applicable, ROTEM = rotational thromboelastometry, UFH = unfractionated heparin.

↑ = increase in laboratory result, ↓ = decrease in laboratory result, ↔ = no change in laboratory result status.

^aHypothermia does not alter results because test is performed at standard 37°C. Whether test result accurately reflects biological activity inpatient is unknown.

^bFor anti-factor Xa assay without added exogenous antithrombin.

^cThere is a threshold above which triglycerides, bilirubin, or hemoglobin will interfere with optical detection systems that is specific for each analyzer. See manufacturers notes for details.