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Difficulty: Very hardHematology and Oncology

A hematology consultation service is reviewing the coagulation profiles of four adult patients, all of whom present with unexplained prolonged coagulation times on routine preoperative screening. Based on the specific specialized laboratory testing kinetics provided, match each patient's coagulation profile to the most accurate underlying pathophysiologic mechanism.

  • Patient 1: Prolonged aPTT. A 1:1 mixing study with normal plasma immediately corrects the aPTT to normal. However, after a 2-hour incubation at 37°C, the aPTT becomes significantly prolonged again.Acquired alloantibody or autoantibody exhibiting time- and temperature-dependent inhibitory kinetics against a specific intrinsic pathway factor.
  • Patient 2: Prolonged aPTT. A 1:1 mixing study with normal plasma fails to correct the aPTT immediately. The subsequent addition of excess hexagonal phase phospholipid normalizes the aPTT.In vitro interference of phospholipid-dependent coagulation by autoantibodies, typically associated with paradoxical in vivo hypercoagulability.
  • Patient 3: Prolonged PT and aPTT. A 1:1 mixing study immediately corrects both parameters. Specific assays reveal severely reduced activities of Factors II, VII, IX, and X.Impaired gamma-carboxylation of glutamic acid residues on specific procoagulant proteins due to an acquired nutritional or toxic etiology.
  • Patient 4: Prolonged aPTT with normal PT. A 1:1 mixing study immediately corrects the aPTT, which remains corrected after a 2-hour incubation. Factor XI activity is measured at <1%.Autosomal recessive deficiency of a contact activation pathway serine protease, frequently presenting with delayed, mild trauma-induced bleeding.

Answer

Patient 1 matches acquired factor VIII inhibitor (time-dependent inhibition). Patient 2 matches lupus anticoagulant (phospholipid interference). Patient 3 matches Vitamin K deficiency (impaired gamma-carboxylation). Patient 4 matches Factor XI deficiency (autosomal recessive contact pathway).
The correct pairings accurately reflect the physiological and biochemical behavior of different hemostatic disorders in the laboratory setting. Mixing studies uniquely distinguish between physical absences of factors (which correct) and the presence of interfering antibodies (which do not correct, either immediately or after incubation).

Step-by-Step Solution

1
Analyze Patient 1's mixing study kinetics.
Initial correction with delayed prolongation indicates a time-dependent inhibitor.
Acquired Hemophilia A (Factor VIII inhibitor) autoantibodies are classically time- and temperature-dependent, initially appearing as a deficiency but revealing their inhibitory nature after incubation.
2
Analyze Patient 2's mixing study kinetics.
Immediate failure to correct indicates an inhibitor; correction with hexagonal phase phospholipid confirms lupus anticoagulant.
Lupus anticoagulants are autoantibodies that directly bind and neutralize the phospholipids used in the aPTT assay reagent, causing an immediate, non-time-dependent prolongation.
3
Evaluate Patient 3's coagulation profile.
Prolongation of both PT and aPTT that completely corrects on mixing indicates a multiple factor deficiency involving Factors II, VII, IX, and X.
These specific factors rely on Vitamin K as a cofactor for the gamma-glutamyl carboxylase enzyme, which allows them to bind calcium and phospholipid surfaces.
4
Evaluate Patient 4's coagulation profile.
Isolated aPTT prolongation that corrects and stays corrected indicates an intrinsic factor deficiency (Factor XI).
A pure deficiency lacks any inhibitory antibodies, so adding normal plasma fully and permanently replenishes the missing factor, resulting in a sustained normal aPTT.

Key Concept

Interpretation of time-dependent versus immediate mixing study kinetics to differentiate coagulation factor deficiencies from acquired inhibitors.
Estimated Time:2m 0s
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Topics

Hematology and Oncology

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