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Mixing Study
Test CodeCPT Codes
85610, 85730
Includes
PTT-LA, Baseline
If Prothrombin Time is prolonged (>13.5 seconds), then an Immediate PT-Mix will be performed at an additional charge (CPT code(s): 85611).
If PTT-LA, Baseline is prolonged (>40 seconds), then an Immediate PTT-LA Mix will be performed at an additional charge (CPT code(s): 85732).
If Immediate PTT-LA Mix corrects, then an Incubated PTT-LA Mix will be performed at an additional charge (CPT code(s): 85732).
Preferred Specimen
Minimum Volume
Instructions
Transport Container
Transport Temperature
Specimen Stability
Refrigerated: Unacceptable
Frozen: 14 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Methodology
Clot Detection
Reference Range
Prothrombin Time | 9.0-11.5 sec |
Immediate PT-Mix | ≤11.5 sec |
PTT-LA, Baseline | ≤40 sec |
Immediate PTT-LA Mix | See Laboratory Report |
Incubated PTT-LA Mix | See Laboratory Report |
Clinical Significance
This test is used to help differentiate coagulation factor deficiency from inhibitor activity in patients with prolonged clotting times-prothrombin time (PT) and activated partial thromboplastin time (aPTT).
Deficiency of a coagulation factor or factors can be congenital or acquired. Congenital factor deficiency is caused by pathogenic variants of the gene that encodes the coagulation factor; acquired factor deficiency is caused by inhibitors that interfere with factor activity. This mixing study can be used to determine the cause of factor deficiency. If the clotting time of the immediate mix remains prolonged ("not corrected"), the presence of an inhibitor is suspected (ie, lupus anticoagulant, factor specific inhibitors, anticoagulant, or other non-specific inhibitors). If the clotting time of the immediate mix is below the cut-off ("corrected"), a factor deficiency is suspected. Because some inhibitors (eg, inhibitors against factor VIII) can only be detected after incubation, an incubated mix may also be included with the aPTT mixing study [1].
This test can be used to guide the investigation of coagulation disorders but has limited sensitivity and specificity [1], specifically if the baseline clotting test is minimally prolonged. Tests for coagulation factors, specific inhibitors, and lupus anticoagulants may be needed for the diagnosis.
Note that the test results may be affected by the titer and strength of inhibitors, number of the deficient coagulation factors, heparin contamination, anticoagulants, direct thrombin inhibitors, or direct Xa inhibitors [1].
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
Reference
1. Higgins RA, et al. Coagulation, anticoagulation, fibrinolysis. In: Rifai R, et al, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier Inc; 2022.
Performing Laboratory
Quest Diagnostics Nichols Institute-San Juan Capistrano, CA |
33608 Ortega Highway |
San Juan Capistrano, CA 92675-2042 |