Specimen:

Plasma

Collection Medium:

Minimum:

Full draw, any size blue top (mix well)  must be at least 90% full.

Testing
Schedule:

0800-1630 Monday through Friday.

Analytic Time:

2 hours (upon receipt in laboratory)

Reference Range:

23-30 seconds

Critical value: 50 seconds (on outpatients only)

Comments:

Must be drawn swiftly with a clean venipuncture  (no hematoma).  Time 
drawn must be indicated on requisition.  Obtain special tube from lab 
if patient's hematocrit is over 55%.  If patient is on heparin therapy, 
samples must be in the lab within one hour after draw.  All other 
samples must be tested within four hours.

Activated Partial Thromboplastin time (aPTT) may be performed on the 
same collection tube as Prothrombin Time and Fibrinogen.

Please print, complete and submit the Advance Beneficiary Notice 
(ABN) along with the Laboratory Requisition before shipping the 
specimen.

The laboratory changed to a new lot of PTT reagent on 2/10/07.  The 
mean of the reference range with this new reagent is 26 seconds; the 
reference range will be 23-30 seconds.  Because of the significant 
variability in response of the aPTT reagent systems to heparin, 40 
patient specimens with heparin levels of 0.3-0.7 U/ml were evaluated by 
an Anti-factor Xa method.  The mean of this group of specimens is 60 
seconds.  The aPTT values range from 38-96 seconds.  The mean of the 
published therapeutic range for heparinization of 1.5-2.5 times the 
mean of the reference range (26) yields values of 39-65 seconds with 
this reagent.  Based on our studies of heparin responsiveness, this is 
a reasonable target range to use with this reagent when treating 
uncomplicated venous thromboembolism.  Regarding the monitoring of 
heparin therapy this reagent represents only a slight change from our 
previous lot of aPTT reagent.

Methodology:

Optical clot detection.

Sample
Processing:

Centrifuge within two hours of draw time.
Aliquot serum/plasma into plastic container and cap (glass is not 
acceptable).
Centrifuge a second time at 3500 RPM for 10 minutes and aliquot into a 
new, labeled plastic tube.

Sample
Storage:

Freeze specimen immediately.

Transport
Instructions:

Place specimen into zip-lock type bag, seal bag.
Place requisition into outside pocket of bag.
Place dry ice on top of specimen in styrofoam container.

CPT Code:

85730

See also:
Prothrombin Time, Plasma

See Additional Information:
Hematology Critical Lab Values
Heparin Therapy
Phlebotomy Tubes and Order of Draw