Prothrombin Time

Collection Instructions:

Specimens must be filled appropriately see this example

Correct ratio of Blood to Citrate is critical (9:1). Specimens must be filled within +/- 10% of stated volume.

If a Blue Top Tube is collected utilizing a butterfly, a Blue Discard Tube must be drawn first to remove air from the line. If this is not done, the Blue Top Tube will not be filled properly due to the vacuum in tube and a redraw will be required.

 

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 5 mL 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.

Rejection Criteria:

Clotted samples

Improperly filled tubes (under or overfilled)

Wrong anticoagulant (3.8% sodium citrate is NOT acceptable)

Patients with hematocrit (HCT) >55% (red cell volume is >1/2 tube volume)

Hemolyzed samples

Whole blood that was refrigerated or placed on ice

DO NOT freeze in a frost-free freezer

Frozen samples that were thawed in transport, or thawed samples that were refrozen