How long should heparin (unfractionated heparin/low molecular weight heparin) be held before drawing blood for a hypercoagulability panel?

How Long to Hold Heparin Before Hypercoagulability Panel Testing

Blood samples for hypercoagulability panel testing should be collected at least 4 hours after cessation of unfractionated heparin infusion and at least 12 hours after a dose of low molecular weight heparin to avoid interference with assay performance. 1

Timing of Heparin Discontinuation Before Testing

• For unfractionated heparin (UFH): Hold for at least 4 hours before blood collection 1
• For low molecular weight heparin (LMWH): Hold for at least 12 hours before blood collection 1
• Patient's sample heparin level should be < 0.2 IU/mL for accurate testing results 1

Rationale for Holding Heparin

• Contamination of blood samples with heparin can interfere with assay performance and lead to inaccurate results 1
• If aggregation is observed in control samples without added heparin, it suggests residual heparin in the patient's sample 1
• Heparin can bind to various proteins involved in the coagulation cascade, potentially masking true hypercoagulable states 1

Sample Collection Recommendations

• Collect blood in both serum and citrate (0.109 M) tubes to allow for comprehensive testing 1
• One serum aliquot should be used immediately for rapid screening, with remaining serum and citrated plasma stored at -80°C for later assays 1
• For heparin-induced thrombocytopenia (HIT) testing specifically, hirudin tubes (25 μg/mL final concentration) are preferred over citrate tubes as they improve assay sensitivity 1

Special Considerations

• If testing for heparin-induced thrombocytopenia (HIT), blood should be collected following the same timing guidelines (≥4 hours after UFH, ≥12 hours after LMWH) 1
• For patients on continuous heparin therapy where discontinuation is not feasible, note the timing of the last dose on the laboratory requisition 1
• If aggregation is observed in the test without heparin, a new sample should be obtained after ensuring adequate heparin clearance 1

Potential Pitfalls

• Inadequate heparin clearance time can lead to false negative results in hypercoagulability testing 1
• Heat inactivation of samples should not be performed as it may decrease antibody titers in HIT testing, resulting in decreased area under the curve (AUC) and increased lag time 1
• Samples with residual heparin levels >0.2 IU/mL may yield unreliable results and require recollection 1

Quality Control Measures

• If testing specifically for HIT, each run should include known negative and positive controls 1
• For inconclusive results, a new patient sample should be taken for repeat testing after ensuring adequate heparin clearance 1
• Document the timing of the last heparin dose on laboratory requisition forms to aid in result interpretation 1