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
85732

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.

Specimen Stability

Platelet Poor Plasma - Room Temp: 4 hours
If delay in testing or requires transport, freeze the Platelet Poor Plasma 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:
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.