Activated partial thromboplastin time (APTT) (UFH monitoring)
Patient plasma is first incubated with a contact activator to activate FXII and commence the intrinsic pathway. Although not a significant reaction in vivo with respect to bleeding, the activated FXII (FXIIa) activates FXI independently of thrombin, which proceeds to activate FIX independently of FVIIa/TF. FIXa generates FXa to begin the 'common' pathway which generates thrombin via the prothrombinase complex to form a fibrin clot. The APTT reagent also contains the 'partial' thromboplastin, comprising phospholipid but not tissue factor, which facilitates reactions involving the vitamin K dependent factors of both pathways but excludes FVII. The process of timing to clot formation begins upon the addition of calcium ions to replace those removed by the tri-sodium citrate anticoagulant and thereby facilitate functioning tenase and prothrombinase complexes.
Our routine APTT reagent, used on automated analysers employing photo-optical clot detection, is lupus anticoagulant insensitive. For rare occasions where interfering factors compromise APTT analysis on the automated analysers, we have an alternative reagent used on a semi-manual coagulometer employing a mechanical clot-detection technique.
APTT is the most commonly used test for UFH monitoring. Between-reagent variability exists for the sensitivity of APTT reagents to the UFH anticoagulant effect
Therapeutic range: 1.5 - 2.5 (ratio)
800µL x 1 aliquot
Internal requests: please refer to EPR label
The sample should be analysed within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling creates a dilution error and leads to inaccurate results.
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH
Laboratory opening times
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT
Outside core hours, contact Duty Haemostasis Biomedical Scientist
Last updated: 10/11/2021