Clinical Lab Handbook

Container/Tube: Light blue-top (3.2% sodium citrate) tube

Specimen Volume: 2.5 mL of sodium citrate whole blood

Transport Instructions:

On Site: Send specimen "room temperature". Must arrive within 2 hrs of collection to meet 4 hr stability window.

Off Campus: Centrifuge and separate. Send plasma frozen in appropriately labeled pour off container.

The activated partial thromboplastin time (aPTT) is a screening procedure for deficiencies in coagulation factors of the intrinsic coagulation pathway, factors VIII, IX, XI, and XII. Severe deficiencies of fibrinogen and factors II, V and X can also be detected by the aPTT. It is a useful and effective method for screening patients with a bleeding tendency, for evaluating the effect of therapy in procoagulant disorders and as the basis for several specific coagulation factor assay procedures. The aPTT is widely advocated as a test for monitoring and regulating unfractionated heparin therapy. The presence of non-specific inhibitors, such as the lupus anticoagulant, may prolong the aPTT; this effect is variable and is generally recognized as being related to the nature and level of the inhibitor present. The aPTT consists of recalcifying plasma in the presence of a standardized amount of platelet-like phosphatides and an activator of the contact factors of the intrinsic coagulation pathway. The aPTT is the time in seconds, required for a fibrin clot to form.

Factors of the intrinsic coagulation system are activated by incubating plasma with the optimal amount of phospholipids and surface activator. The addition of calcium ions triggers the coagulation process and the clotting time is then measured.

85730

Critical value (automatic call-back): >100 seconds

Monday through Sunday

Available STAT

Note:

1. Excessively high or low hematocrit will affect results.

2. Tube must be completely filled to ensure proper ratio of blood to anticoagulant and to avoid erroneous results.

3. Use and discard a light blue-top tube (in order to fill tubing) when drawing with a butterfly needle.