Sign in →

Epic Test Code LAB326 Mixing Study: PTT

Important Note

Please test PTT on same day of collection before sending frozen sample to MIB.

Performing Location(s)

BMC

Specimen Type

Plasma

Preferred Container

FOUR 3.2% sodium citrate plastic blue top tubes, 4.5 mL each (one set of 4 is sufficent if both MXPT and MXPTT are ordered)

Blood Tube Draw Volume

Min 90% draw volume  

Minimum Volume to Submit for Testing

4.5 mL plasma

Transportation Needs

If transportation to the laboratory is to be delayed for more than 1 hour:

Prepare Platelet Poor Plasma.

1.Centrifuge tube at 1500g for 10 minutes.
2.Use a plastic transfer pipet to remove plasma (staying away from buffy coat layer) to transfer top 2/3 of plasma to plastic aliquot tube
3.Place plasma from the 4 tubes together in one aliquot tube
4.Centrifuge aliquot tube at 1500g for 10 minutes.
5.Transfer top 3/4 of plasma (do not disturb button at bottom of tube) into 2 or more plastic aliquot tubes.
6.Label appropriately with patient information and PLASMA sticker
7.Freeze immediately at -15° to -25°C freezer until ready for transport
8.Plasma must be transported to the laboratory frozen.

 

RMP  to  G force Converter

Causes for Rejection

Clotted specimens
Mislabeled or unlabeled specimens
Collection in any tube other than 3.2% plastic sodium citrate blue top tube
Less than 90% filled
Received greater than 4 hours old unless separated from cells and frozen at -15° to -25°C or less than -70°C
Hemolysis > 500 mg/dL (>4+)
Whole blood or Plasma samples received refrigerated (2-8° C) or on ice
Patients who are currently on anticoagulation therapy

Normal APTT

Whole blood or plasma samples received refrigerated (2-8 degree C) or on ice.

Limitations

The mixing study is only a qualitative screening assay used to distinguish factor deficiency from the effects of an inhibitor and cannot be used to rule out either entity. Occassionally, both factor deficiency and inhibitor may coexist.
When the baseline aPTT is only minimally prolonged, the results may be misleading.
Mild factor defects or low titered/time and temperature inhibitors may be difficult to discern and usually require further investigation.
Interference from heparin, heparin flushes and coumadin should be ruled out.

  • Many commonly administered drugs may affect APTT results and further studies should be made to determine the source if unexpected abnormal results.
  • Hemoglobin >500 mg/dL
    Bilirubin > 26 mg/dL
    Triglycerides > 1000 mg/dL. Grossly lipemic specimens can be ultra centrifuged.
  • Intrinsic Factor Sensitivity- Studies have shown SynthASil to be sensitive to decreased concentration of intrinsic factors resulting in an abnormal APTT value when factors VIII, IX, XI, and XII levels were in the 35-60% range.
  • Lupus anticoagulants and certain factor deficiencies (e.g.XII), may prolong baseline PTT and/or accentuate prolonged PTT in the presence of heparin. In these situations, the heparin Anti-Xa assay should be used to monitor heparin therapy.

Reference Values

Interpretive Guidelines:

  • Interpretive report may be issued by the Pathologist.
  • Correction of the test plasma by the addition of PNP into or within 3 seconds of the normal range for the PTT may indicate factor deficiency.
  • Failure of the PNP to correct PTT may indicate the presence of an inhibitor.

Days of Analysis

Mon-Fri
Day Shift

Available STAT

No

Includes

Interpretive report of an APTT assay performed on the patient’s sample after the addition of pooled normal plasma (50:50)

Methodology

Turbidimetric

CPT Code

85732

Last Updated

30-Apr-19