Activated Partial Thromboplastin Time

Clinical Significance

Screening for deficiencies or inhibitors of the coagulation system. 
Monitor the dosing effect of unfractionated heparin therapy.

Client Notes

If patient is on unfractionated heparin the specimen will need to be to the testing laboratory within 45 minutes of collection.  

Specimen Requirements

2.7 mL Whole Blood in a Blue Top Tube - 3.2% Buffered Sodium Citrate

Transport And Storage

Patients receiving unfractionated heparin (UFH):

1. Must be centrifuged to produce PPP within ONE hour of collection.
2. Centrifuged samples are stable 4 hours ambient.
   1. If testing will be performed at another testing location the PPP plasma should be transfered to a plastic vial. Send both tubes together to testing site.
   2. If testing will not be completed in 4 hours then PPP should be frozen. Do not freeze in frost free freezer.
      • 2 weeks at -20C
      • 12 months at -70C

Patients not receiving heparin whole blood is stable up to 24 hours ambient.

Collection Instructions

Specimens must be filled appropriately see this example

Correct ratio of blood to citrate is critical (9:1). Tube must be filled to the minimum fill indicator mark on the tube. Do not overfill.

If utilizing a butterfly to collect, a blue top discard tube must be drawn first to remove air from the line. If this is not done, the collection blue top tube will not be filled properly due to the vacuum in tube and a redraw will be required

   Heparinized patient specimens must be spun within 1 hour of collection - Follow Platelet Poor Collection

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 5mL 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.

Minimum Volume

1.8 mL Whole Blood in a Clear Blue Top Tube

Neonatal Volume

1.8 mL Whole Blood in a Clear Blue Top Tube

Reference Range:

23.5 - 33.0 seconds

Therapeutic range for pre-mixed heparin is 50.0-70.0 seconds.  seconds. Heparin therapeutic range is based on the APTT range corresponding to a heparin concentration of 0.3 to 0.7 Units/milliliter determined by Factor Xa inhibition assay.

Critical Ranges:

>= 110.0 Seconds

Methodology:

• Photo Optical

Clinical Significance

Screening for deficiencies or inhibitors of the coagulation system. 
Monitor the dosing effect of unfractionated heparin therapy.

CDM

01450046

CPT Coding

85730

Medical Necessity May Apply