Table 3 Main advantages and limitations of APTT and anti-Xa activity for UFH treatment laboratory monitoring
From: Management of the thrombotic risk associated with COVID-19: guidance for the hemostasis laboratory
| Advantages | Limits | |
|---|---|---|
| APTT |
- largely available, low cost - sensitive to clinically relevant changes of coagulation (coagulation proteins increases or deficiencies) | - numerous interferences; optical methods can be unreliable in case of DIC |
| - heparin sensitivity is highly reagent dependent | ||
| - APTT prolongation target needs to be established for each new batch of reagents | ||
| - APTT before UFH needed | ||
| - clinically irrelevant changes, or of dubious clinical relevance | ||
| APTT prolonged with: | ||
| • presence of antiphospholipid antibodies (viral infections) | ||
| • high CRP (depending on the reagent) | ||
| • high plasma levels in FDPs | ||
| • preanalytical (e.g., heparin/EDTA contamination, under-filling, delayed centrifugation, hypertriglyceridemia, hyperbilirubinemia) | ||
| APTT shortened with: | ||
| • preanalytical (e.g., prolonged venous stasis, vigorous mixing, coagulation of the sample, PF4) | ||
| • high factor VIII levels | ||
| Anti-Xa activity |
- less vulnerable to biological interferences - no requirement for measurement before UFH administration | - preanalytical interferences: PF4*; free hemoglobin and bilirubin if significant elevation |
| - insensitive to fluctuations in the underlying coagulation state (i.e., coagulation factor increases or defects), of potential clinical relevance | ||
| - AT deficiency (e.g. in sepsis): risk of heparin underdosing with kits containing exogenous AT; sensitivity to endogenous AT not evaluated with kits that do not contain exogenous AT | ||
| - variability in reagents composition (AT, dextran…) | ||
| - therapeutic range poorly defined | ||
| - not validated in hyperinflammatory states | ||
| - less available, more expensive |