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PTT
Test CodePTT2
Alias/See Also
Partial Thromboplastin Time, APTT, Activated Partial Thromboplastin Time
Preferred Specimen
4.5 mL blood (9:1 blood to anticoagulant) in 5 ml tube
Instructions
Tube must be filled to the line to ensure the proper ratio of blood to anticoagulant.
NOTE: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
NOTE: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
Transport Container
3.2% Sodium Citrate (light blue-top)
Specimen Stability
Room temperature: 4 hours (2 hours if on heparin therapy), Refrigerated: not recommended, Frozen platelet-poor plasma: 2 weeks
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Moderate or grossly hemolyzed specimens are unacceptable.
Limitations
Many commonly administered drugs may affect the results obtained in APTT testing. (Example: heparin and coumadin). When monitoring heparin therapy, any release of platelet factor 4 (PF4) which is a potent inhibitor of heparin, represents a potential source of error. A congenital or acquired inhibitor may prolong the APTT.
Reference Range
23-37 seconds
Clinical Significance
The activated partial Thromboplastin time (APTT) is a general coagulation-screening test of the intrinsic coagulation pathway (factors XII, XI, IX, VIII, X, V, II, and fibrinogen). The main application of the APTT is to detect congenital and acquired deficiencies of these factors and to monitor the heparin therapy. The APTT is more sensitive and reproducible than other screening tests, such as plasma recalcification and partial thromboplastin time, due to the control of contact activation and platelet phospholipid concentration. A prolongation of the APTT is encountered in the following situations: Congenital deficiencies of factors VIII, IX, XI, and XII, Liver diseases, consumptive coagulopathy, circulating anticoagulants, during heparin or oral anti coagulant therapy.
