Laboratory Test Directory

Activated Partial Thromboplastin Time: (089-0220)

Useful in monitoring unfractionated heparin therapy and detecting abnormalities of the intrinsic clotting pathway.

 APTT

 Electromagnetic Viscosity Detection

 Samples are accepted 24 hours per day at Sample Management, 5.136 McCullough Bldg.

 STAT: 1 hour; ROUTINE: 4 hours

Collect: Routine venipuncture; discard 1st mL of blood or collect other tubes (purple top, red-topped) prior to collecting sample in blue-topped (3.2% sodium-citrate) tube.

Specimen Preparation:  Samples should be received in laboratory within ½ hour of draw for best results.  Acceptable up to 4 hours after draw, at ROOM TEMPERATURE.

Specimen: Blood

Volume: 2.7ml

Minimum Volume: Call Lab

Storage/Transport: NOTE:  If delivery time is to be greater than 4 hours from time of draw, centrifuge the specimen for 15 minutes at 2000-2500g.  Separate the plasma from the cells and snap freeze (-20⁰C) the plasma. For patients on heparin therapy, the blood  must be centrifuged and the plasma  separated  from cells within 1 hour of collection.

Stability:  Plasma 4 hrs at 20 +/- 5°C.   Patients on heparin therapy -plasma is stable  for 2 hrs at 20 +/- 5°C  when collected in 3.2% sodium citrate (blue top).   Frozen plasma  2 Weeks at -20°C.  Frozen plasma 12 months at -70°C  or colder

Causes for Rejection: QNS, clotted, severely hemolyzed, greater than 4 hours old, wrong tube (3.8% sodium citrate), high hematocrit (> 55%), identification error, processed and/or stored improperly.

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/hem/ACTIVATED_PARTIAL_THROMBOPLASTIN_TIME.htm or contact laboratory [409-772-3314] for further recommendations.

23 - 38 seconds

 85730  Limited Coverage Test (NCD)

When ordering tests for which Medicare or Medicaid reimbursement will be sought, physicians should only order tests that are medically necessary for the diagnosis or treatment of the patient.  Components of the organ or disease panels may be ordered individually.  The diagnostic information must substantiate all tests ordered and must be in the form of an ICD-9 code or its verbal equivalent.

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