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APTT Equal Mix
MessagePerforming Lab: Regions
Test Code
3531
Alias/See Also
Sunquest: APTTM; APTT 1:2 Dilution, PTT Mix
CPT Codes
85730
Includes
APTT;PTT MIX; PTT Normal Plasma
Preferred Specimen
2.7 mL (in 3 mL tube) 3.2% Sodium Citrate Plasma (light blue-top) tube filled to fill line on the tube
Minimum Volume
1.0 mL plasma aliquot per test
Other Acceptable Specimens
1.0 mL platelet poor plasma (Frozen)
Instructions
Processing: Freeze an aliquot of platelet poor plasma at -20°C if not performed within 4 hours of collection
Centrifuge light blue-top tube for 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/mcl). Freeze immediately and ship on dry ice.
Centrifuge light blue-top tube for 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/mcl). Freeze immediately and ship on dry ice.
Transport Container
Transport processed samples frozen on Dry Ice
Transport Temperature
Frozen if >4 hours old
Specimen Stability
Room Temperature: 4 hours Refrigerated: 4 hours Frozen 72 hours at -20C or 2 weeks at -80C
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolyzed or Clotted Samples, Samples do not meet the minimum draw requirements, Samples exceed maximum draw requirements, Samples with hematocrit >55% not collected with the special tube. Sample from patients on unfractionated Heparin Therapy, Direct Xa inhibitors or Thrombin inhibitors.
Methodology
APTT assay of patient/normal plasma mixture at l:2 dilution
Setup Schedule
Daily
Report Available
Same day.
Limitations
If the patient’s hematocrit is greater than 55%, special tubes with less anticoagulant must be used for specimen collection
Reference Range
An equal mix with pooled plasma should normalize the APTT. If the patient’s abnormal APTT is due to a factor deficiency, the 1:2 mix should bring the APTT into the normal range. Specific factor assays can then be done. If the APTT mix does not normalize, an inhibitor/antibody should be considered, along with patient history.
Clinical Significance
Mixing equal amounts of normal plasma with patient plasma will correct an abnormal protime when it is caused by a factor deficiency (including Coumadin therapy). If the protime does not correct sufficiently, there may be an inhibitor or antibody present. In either case, the results of an equal mix will be a guide for further testing.
