PT 1:1 MIXING STUDIES

Message

Coagulation

Test Code

LAB321

Alias/See Also

Prothrombin Time 50:50, PT 50:50, Corrected PT, PTCOR

CPT Codes
85611

Preferred Specimen

2.7 ml. whole blood (blue top tube, citrate)
***Tube must be full

Instructions

To rule out Coagulation Factor deficiencies. Special order by physician ONLY.
*NOTE: If ordering with Protime/INR, must order the Mixing Studies using Priority "STAT" to prevent duplication of components.

LAB: Use validated Centrifuge for Platelet Poor Plasma and aliquot citrated plasma to alternate tube. Deliver to department for analysis.

Specimen Stability

Room Temp: 4 hours
If delay in testing or requires transport, freeze at -20C for up to 2 weeks.

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

Underfilled tube - Quantity not Sufficient (QNS)
Clotted specimen

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:
PT Reference Range: 9.4 - 12.5 seconds
Rosner Index result is < 12. Use Rosner Index (RI) Formula:
[ (PT MIX - PT NPP Ctrl) ] X 100 / [Neat PT]
< 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.