Pathology · Year 2 · from Pathology

Case 2: Coagulation Workup - Prolonged PTT

Patient Demographics

• Age: 8 years
• Sex: Male
• Occupation: Second-grade student

Chief Complaint

"He's having surgery next week and his preoperative blood work came back abnormal."

History of Present Illness

An 8-year-old boy is referred for evaluation of an isolated prolonged PTT discovered on preoperative labs for an elective tonsillectomy. His PTT is 58 seconds (normal 25-35 seconds), and his PT is normal at 12 seconds. He has no history of abnormal bleeding. His mother reports that he has had multiple dental extractions without excessive bleeding, normal healing from cuts and scrapes, and no spontaneous bruising or bleeding. He has never had surgery before. There is no family history of bleeding disorders.

Past Medical History

• Recurrent tonsillitis (indication for surgery)
• No prior surgeries or significant bleeding
• No prior transfusions

Family History

• No known bleeding disorders
• No history of excessive bleeding in parents or siblings

Physical Examination

• Vital Signs: Normal for age
• General: Well-appearing boy
• Skin: No petechiae, purpura, or ecchymoses
• Joints: No hemarthroses or swelling
• Lymph: Enlarged tonsils
• Otherwise unremarkable

Laboratory Workup

Initial Coagulation Studies:

Systematic Approach to Prolonged PTT

Step 1: Understand What PT and PTT Measure

Isolated prolonged PTT (normal PT) indicates:

• Deficiency or inhibitor affecting intrinsic pathway factors (XII, XI, IX, VIII)
• Does NOT affect common pathway (or PT would also be prolonged)

Step 2: Perform Mixing Study

A mixing study determines whether the prolonged PTT is due to a factor deficiency or an inhibitor:

• Patient plasma is mixed 1:1 with normal pooled plasma
• The mixture is tested immediately and after 1-2 hours incubation

Mixing Study Results:

Interpretation:

• Correction = Factor Deficiency (normal plasma provides the missing factor)
• No correction = Inhibitor present (antibody inhibits factor in mixed sample)

This patient's mixing study CORRECTS, indicating a factor deficiency, NOT an inhibitor.

Step 3: Identify Which Factor is Deficient

Individual Factor Assays:

Diagnosis

Factor XII (Hageman Factor) Deficiency

Clinical Significance

CRITICAL TEACHING POINT: Factor XII deficiency causes a markedly prolonged PTT but does NOT cause clinical bleeding.

Why Factor XII Deficiency Doesn't Cause Bleeding:

• Factor XII is important for in vitro (test tube) coagulation
• In vivo, coagulation is primarily initiated by tissue factor (extrinsic pathway)
• Factor XII is not required for normal hemostasis
• Patients with factor XII deficiency have NORMAL surgical outcomes

Historical Note:

• John Hageman, in whom the deficiency was first described, had no bleeding problems
• Ironically, he died of pulmonary embolism (thrombosis, not bleeding)

Factors That Prolong PTT Without Bleeding Risk

Conditions That Prolong PTT (Differential Diagnosis)

Factor Deficiencies (mixing study corrects):

• Factor VIII deficiency (Hemophilia A) - DOES bleed
• Factor IX deficiency (Hemophilia B) - DOES bleed
• Factor XI deficiency - Variable bleeding
• Factor XII, prekallikrein, HMWK - NO bleeding

Inhibitors (mixing study does NOT correct):

• Lupus anticoagulant (antiphospholipid antibodies)
• Paradoxically causes thrombosis, not bleeding
• PTT prolonged in vitro only
• Specific factor inhibitors (e.g., acquired Factor VIII inhibitor)
• DOES cause bleeding

Other:

• Heparin contamination (common in hospitalized patients)
• von Willebrand disease (vWF carries Factor VIII)

Management for This Patient

Recommendations:

1. Surgery can proceed as planned - Factor XII deficiency does not increase bleeding risk
2. No factor replacement needed
3. No special precautions required
4. Document in medical record to avoid future unnecessary workups
5. Family screening optional (autosomal recessive inheritance)

Counsel Family:

• Reassure that this is a benign laboratory finding
• No clinical bleeding disorder
• Future surgeries and procedures are safe
• If asked, can explain that "the blood test measures clotting in a test tube, but your son clots normally in his body"

Clinical Pearl

An isolated prolonged PTT must always be investigated with a mixing study to differentiate factor deficiency from an inhibitor. If the mixing study corrects, factor assays identify the specific deficiency. Factor XII deficiency is clinically benign and does not cause bleeding - surgery can proceed safely. Similarly, lupus anticoagulant prolongs PTT but causes thrombosis, not bleeding. Always correlate laboratory findings with clinical bleeding history. A patient with severe prolonged PTT but no bleeding history likely has Factor XII deficiency or lupus anticoagulant - neither requires treatment for bleeding prevention. In contrast, hemophilia A and B (Factor VIII and IX deficiencies) cause severe bleeding and require factor replacement before procedures.

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