Partial Thromboplastin Time Mixing Study

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Primary Name	Partial Thromboplastin Time Mixing Study
Synonym	Activated partial thromboplastin time mixing study
Synonym	Partial thromboplastin time substitution
Contraction	PTT mix
Contraction	APTT mix
Contraction	PTT substitution
UAB Procedure Number	2500168
CPT Code	85732
Specimen	Collect one (1) blue-stopper tube (3.2% sodium citrate), filled to specified volume. Do not underfill or overfill.
Specimen Management	Centrifuge blue-stopper tube within one (1) hour of collection, separate plasma and test or quick-freeze at -70°C.
Specimen Accepted	Daily including weekends
Times Available	0730-1600
Test Performed	Monday through Friday
Available Stat?	Pathologist approval required
Description	PTT mixing study is indicated when the PTT is prolonged in the absence of heparin therapy. The test is preceded by a thrombin time to detect therapeutic heparin or a direct thrombin inhibitor. Patient plasma is mixed with normal plasma, the mixture is incubated, and the PTT is repeated. If the mixture's PTT result does not correct, the patient may have an inhibitor. There are specific inhibitors such as anti factor VIII, associated with bleeding, and lupus anticoagulants, associated with thrombosis. If the mixture's PTT result does correct, the patient may have a coagulation factor deficiency. The results of the PTT mixing study are used to direct further studies in consultation with the ordering physician.
Reference Interval	Correction suggests factor deficiency. No correction suggests presence of an inhibitor.
Critical Value	--
Therapeutic Range	--
Follow-up Test	If PTT corrects, follow up with factor assays. If PTT does not correct, follow up with lupus anticoagulant testing.
Associated With	Coagulation factor inhibitors
Associated With	Bleeding disorders
Associated With	Venous thrombosis
Associated With	Lupus anticoagulant