PTT 1:1 MIXING STUDIES

Message

Coagulation

Test Code

LAB326

Alias/See Also

APTT 50:50, PTT 50:50, Corrected APTT/PTT PTTCOR

CPT Codes
85730

Preferred Specimen

2.7 ml. whole blood (blue top tube, citrate) MUST BE FULL.

Instructions

To rule out Coagulation Factor deficiencies. Special order by physician ONLY.
*NOTE:

If ordering with APTT, must order the Mixing Studies using Priority "Timed" to prevent duplication of components.
Patients with in-dwelling catheters should have coagulation studies drawn from the catheter unless specified "peripheral" by the physician.
Procedures for in-dwelling catheter draw: 1. If ONLY a coagulation test is required, the first 20 ml. of blood drawn must be discarded before the specimen for coagulation testing can be obtained. 2. If specimens for other laboratory tests IN ADDITION to a specimen for coagulation testing are required, the first 8 to 10 ml. of blood drawn must be discarded. A second syringe of blood can then be obtained for all tests other than the coagulation test (e.g. Chemistry, Hematology, Blood Bank, or Microbiology). Following that, a third syringe should then be used to draw the coagulation sample.

LAB: Centrifuge in validated Platelet Poor Plasma Centrifuge for 2 minutes at 7200 rpm. Specimen to be delivered to Coagulation department STAT. Notify CLS upon arrival.
**Testing must be completed within 24 hours of collection.

Note: If unable to deliver whole blood to testing laboratory within stability time, platelet poor plasma should be aliquoted and placed in freezer. Centrifuge light blue-top for 2 minutes at 7200 rpm (STAT Coag centrifuge) 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 aliquoted plasma a second time and transfer platelet-poor plasma into a new plastic vial and freeze at -20℃. Once thawed, specimen must be tested within 2 hours.

Freeze aliquot at -20℃ for at least 1 hour when sending to alternate campus for testing.

Transport Container

Frozen: processed platelet poor plasma

Transport Temperature

Frozen (-20℃): plasma frozen for at least 1 – 2 hours

Specimen Stability

Processed Platelet Poor Plasma:

Room Temp (15-25° C)	4 hours
Refrigerated (2-8°C)	Unacceptable
Frozen (-20°C)	2 weeks

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Hemolyzed, clotted specimen, contaminated, not enough volume, overfilled tube, whole blood specimen transported on ice

Methodology
This is a 1:1 screening procedure (with no incubation mix reflex) to determine whether a prolonged Protime or APTT is caused by a Factor Deficiency or the presence of an inhibitor. If a 50% dilution of the patient's plasma with normal plasma corrects the prolonged test (APTT or PT), it is suggestive that the normal plasma has supplied the missing/deficient factor, but does not rule out the presence of an inhibitor since there is no incubated mix reflex testing performed. If the prolonged test does not correct on 1:1 mix, an inhibitor or multiple factor deficiencies may be present in the patient's plasma.

Report Available

Same day

Reference Range

Mixing Study is considered "Corrected" if any of the following apply:
Clotting time of mix returns to within reference interval:
PTT Reference Range: 25 – 37 seconds
Rosner Index result is < 12. Use Rosner Index (RI) Formula:
[ (PTT MIX - PTT NPP Ctrl) ] X 100 / [Neat PTT]
< 12: Correction; factor deficiency
12 - 15: Indeterminate; retest
> 15 Presence of Inhibitor "Correction" indicates single or multiple factor deficiency(ies).

Clinical Significance

Note: Multiple factor deficiencies may cause mixing study non-correction, which could be incorrectly interpreted as an inhibitor
APTT PT Factor Deficiency
Prolonged Normal Factors VIII, IX, XI, XII
Prolonged Prolonged Factors II, V, X
Normal Prolonged Factor VII

Performing Laboratory
HHN Laboratory
HHI Laboratory

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.