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Test Code PTTB Activated Partial Thromboplastin Time

Specimen Type



Light blue top tube, 3.2% sodium citrate

Preferred Volume

2.7 mL

Offsite Collection Instructions

Whole blood sample must arrive in the laboratory within three hours of specimen collection.


If transport time exceeds three hours, follow centrifugation instructions:

  • Samples must be centrifuged at >1500 x g for 10 minutes at room temperature.
  • Carefully remove the plasma from the cells using a plastic transfer pipette avoiding the buffy coat.
  • Aliquot removed plasma into 2 plastic tubes containing a minimum of 500 uL of specimen in each tube.
  • The plasma samples must then be frozen at -20ºC.
  • Once solidly frozen, they must be shipped on dry ice. Samples that have thawed in transit will be rejected.

Note: For clients who do not have access to dry ice DO NOT freeze the specimen. Follow the centrifugation instructions and send fresh plasma or send whole blood sample. It now becomes vital that the specimen arrives in the lab within three hours of collection.

UCMC Collection Instructions

Specimens may be collected and sent to the laboratory at any time.

Test can be added on to an existing order up to 4 hours following the time of blood draw.



Turnaround Time

STAT: 60 minutes

Routine: 4 hours

STAT Availability


STAT Turnaround Time

1 hour

Test Methodology


Additional Information

All 3.2% sodium citrate light blue top tubes require a ratio of 9 parts blood to 1 part anticoagulant (example: a 3.0 mL tube requires 2.7 mL blood added to 0.3 mL of anticoagulant).

For monitoring of heparin therapy with the frequently employed target range of 0.3-0.7 anti-Xa Units/mL (e.g., for treatment of venous thrombosis), the corresponding aPTT range is currently 62-91 seconds. Anti-Xa of 0.35 Units/mL corresponds to 66 seconds. For the lower intensity anticoagulation range of aPTT 50-70 seconds (e.g., as in guidelines from the American College of Chest Physicians), the corresponding range is currently 0.13-0.41 anti-Xa Units/mL.

CPT Code


Test Includes

Activated Partial Thromboplastin Time (aPTT)

Reference Range

24.0-34.0 seconds

Critical Results

>100.0 seconds

Coverage Information

CMS has established a national coverage policy (NCD) for Medicare for this test as of November 25, 2002. Please document medical necessity. For more details click this link:ncd-details.aspx

Minimum Volume

2.7 mL


For pediatric patients = 1.8 mL


Fee Code



aPTT; PTT; activated Partial Thromboplastin Time