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Laboratory Test Directory

APTT Mixing Studies


Name Method Department Units
APTT Mixing Studies Clot detection
Core Lab, Coagulation sec

Specimen Requirements

Platelet poor plasma

Container Type Container Size Specimen Volume

Blue plastic tube (Citrate)

2.7 mL 6 mL

Frozen - 2 week(s)

Specimen Preparation

  • Fill tubes to appropriate mark.
  • Mix by gentle inversion immediately after collection
  • Centrifuge, remove plasma/serum and freeze
  • Plasma must be platelet free

Reasons for Rejection

  • Over or under filled tube
  • Clotted specimen
  • Not received within specified time frame
  • Gross hemolysis
  • Wrong collection tube
  • Specimen collected in glass tube
  • Capillary specimen
  • Current treatment with Unfractionated Heparin
  • Heparinized specimens


Two 2.7 mL Blue plastic tubes (citrate) are required for this test. Test will be performed only if baseline APTT is elevated. Baseline APTT will be ordered and charged (CPT 85730). Interpretation of results is not valid or possible on patients receiving heparin therapy. Centrifuge citrate tubes according to Lab policy, remove platelet-poor plasma, pool the plasma, aliquot and freeze. Send a minimum of two (2) aliquots of plasma. Reflexive testing may include one or more Quantitative Factor Assays (CPT 85240, 85250, 85270, 85280), Dilute Russell Viper Venom (CPT 81613), and/or Hexagonal Phase Phosphatidylethanolamine (CPT 85372) ordered by the Pathologist. A pathologist's interpretation, billed through Pediatric Pathology Associates (PPAC), may be ordered and charged.

CPT Code

  • 85732 (x4)