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Test Code PTTMX PTT Mixing Study

Specimen and Container/Tube

Specimen Type: Plasma

Preferred Specimen: Light Blue Top Tube, 3.2% Sodium Citrate

Other Acceptable specimens: N/A

Specimen Handling and Transport Instructions

UCMC Onsite Instructions: 

Collect specimen per standard collection procedure and send to laboratory immediately. 

 

NOTE: Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.

 

UCMC Offsite and UC MedLab Outreach Instructions: 

  • Collect specimen per standard collection procedure.
  • Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.
  • Centrifuge specimens at >2500 x g for 10 minutes at room temperature.
  • Carefully remove plasma from cells using a plastic transfer pipette avoiding buffy coat.
  • Aliquot removed plasma into 2 plastic tubes containing a minimum of 0.5 mL of specimen in each tube.
  • 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.

Rejection Criteria

  • Common specimen rejected situations include: incorrect specimen type, insufficient volume, missing or incomplete specimen identifiers, incorrect specimen transport, or specimens outside stability limits. 
  • Specimens that have wrong ratio of blood to anticoagulant (fill volume), clotted or grossly hemolyzed.

Reference Values

 

Test

Age

Sex

Reference Range

aPTT

ALL

ALL

25.0 - 34.0 seconds

Immediate PTT Mix

ALL

ALL

<34.1 seconds

Incubated PTT Mix

ALL

ALL

<15.0%

PTT Mix Interpretation

ALL

ALL

N/A

Critical Values

Analyte

Unit

Low

High

Age

aPTT

seconds

N/A

>120.0

All

CPT Codes

85730, 85732, 85390

LOINC Codes

14979-9, 5946-9

 

Volume

Preferred Volume: 2.0 mL

 

Minimum Volume: 1.5 mL

Specimen Stability

Storage Temperature

Stability

Room temperature

4 hours

Refrigerated

not acceptable

Frozen

30 days

Collection Instructions

Collect specimen per standard laboratory collection procedures. 

 

NOTE: Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.

Clinical Indications

Screening for intrinsic coagulation factor deficiencies (factor VIII, IX, XI or XII).

 

Detecting coagulation inhibitors such as lupus anticoagulant, antiphospholipid antibodies, specific factor inhibitors.

Methodology

Clotting

Additional Information

If immediate aPTT mix is prolonged, thrombin time and heparin removed thrombin time will be performed to exclude the presence of heparin. 

 

If immediate aPTT mix is normal, an incubated mix will be performed to investigate for time- and temperature-dependent inhibitors.

 

The UCM Coagulation Laboratory on-service pathologist will review aPTT mixing studies and provide an interpretive report, as indicated.

 

All 3.2% sodium citrate light blue top tubes must have 9 to 1 ratio of blood to anticoagulant.

Turnaround Time

Turnaround times are relative to the time the specimen is received in the test laboratory. 

STAT Turnaround Time: N/A

 

Routine Turnaround Time: 8 hours

 

Testing Schedule: 7 days a week 8:00 am to 10:30 pm

Synonyms/Keyword Search

aPTT Mix, aPTT mixing study, activated Partial Thromboplastin Time Mixing Study

Last Review Date

05/28/2024