The Laboratory and the New Oral Anticoagulants

BACKGROUND: The new oral anticoagulants (NOAs) dabigatran, rivaroxaban, and apixaban have proved effective and safe when used in clinical trials, without a need to adjust the dose in response to laboratory testing. This demonstrated efficacy does not necessarily mean that the laboratory, considered the mainstay for the management of the old anticoagulants, will no longer play a role in treatment with NOAs. CONTENT: Laboratories are involved in the management of anticoagulants in 2 ways. The first, monitoring, implies laboratory testing to assess the drug's effect and to adjust the dosage to maintain anticoagulation within the therapeutic interval. This consideration applies to the old drugs. The second way, measurement, implies laboratory evaluations of drug effect to determine whether patients are under- or over-anticoagulated, information that can be useful for decision-making in special circumstances. The latter applies to NOAs. SUMMARY: Measurements of the effect of NOAs are indicated in several situations: (a) patients with adverse events (i.e., thrombotic/hemorrhagic), particularly those who present with overdosage owing to excessive drug intake or decreased clearance; (b) patients undergoing surgical procedures for ensuring that no residual drug remains in the circulation; (c) patients requiring anticoagulation reversal because of life-threatening hemorrhage; (d) patients with renal insufficiency, who are likely to accumulate the drug in the circulation; (e) patients with liver failure, because NOAs are metabolized by the liver; (f) patients taking other drugs that might increase/decrease the effects of NOAs via drug-drug interactions. The choice of tests is based on such characteristics as availability, linearity of the dose-response curve, standardization, and responsiveness to increasing drug dosage. Practitioners need to be aware that NOAs can interfere with the measurement of common hemostasis parameters.