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ACTIVATED PARTIAL THROMBOPLASTIN TIME (089-0220) Synonyms: APTT, PTT Limited Coverage Test (NCD) CPT 4 Code: 85730 Test Order Mnemonic: APTT Applies To: Useful in monitoring unfractionated heparin therapy and detecting abnormalities of the intrinsic clotting pathway. Test Includes: Mean lab control, patient result. Request Form: Hematology A Collection: Routine venipuncture. Discard 1st ml of blood or collect other tubes (EDTA, Serum-separator, etc.) prior to collecting sample in citrate (light blue-top tube). Storage Instructions: Viable for 4 hours at room temperature. If time from draw to delivery is to be greater than 4 hours, centrifuge the sample, separate the plasma from cells, and snap freeze (-70°C) the plasma. Snap frozen plasma is viable indefinitely. Causes for Rejection: QNS, clotted, severely hemolyzed, greater than 4 hours old, identification error, processed and/or stored improperly. Availability: Accepted 24 hours/day at Sample Management, Room 5.136 McCullough. Turnaround Time: STAT: 1 hour ROUTINE: 4 hours Special Instructions: Deliver sample to lab within ½ hour for best results. Accepted up to 4 hours at room temperature. Specimen: Blood Volume: 4.5 ml Min Volume: Call Lab Container: Sodium citrate tube (light blue-top) Reference Range: 23 - 38 seconds Therapeutic Range: Currently, the activated Partial Thromboplastin Time (aPTT) is the laboratory test most commonly used to monitor unfractionated heparin therapy. The Heparin Therapeutic Range is developed utilizing a procedure derived from Brill-Edwards, et al, in which aPTT values and heparin levels are obtained from patients actually receiving heparin. A graph is prepared that correlates the aPTT in seconds to the heparin Anti-XA units. The ranges established, are the time in seconds equivalent to 0.1 to 0.3 and 0.3 to 0.7 Anti-XA units of heparin. Therapeutic Range = 0.1 Units = 44 seconds (aPTT) 0.3 Units = 63 seconds (aPTT) 0.7 Units = 101 seconds (aPTT) However, prolongation of the aPTT does not necessarily indicate that the blood is effectively anticoagulated in vivo. A variety of conditions can complicate the administration and monitoring of unfractionated heparin therapy. Refer to Monitoring Heparin Therapy in Lab Survival Guide http://www.utmb.edu/lsg/LabSurvivalGuide/hem/ACTIVATED_PARTIAL_THROMBOPLASTIN_TIME.htm or contact laboratory [409-772-3314] for further recommendations. Critical Values: >70 seconds (if patient is not on anticoagulant therapy) Test Method: Electromagnetic Viscosity Detection Interfering Substances: Anticoagulant therapy, circulating anticoagulants. 8/10/2007 |
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