Family Medicine Board Review · Hematology · Source: AAFP 11/2024

Bleeding & Bruises + Von Willebrand Disease

ISTH-BAT screening thresholds, platelet vs. coagulation bleeding patterns, the PT/aPTT interpretation logic, drug-effect lab table, and the full VWD workup and management.

Screening Tool Platelet vs. Coagulation Disorder Medication Causes Physical Examination Prolonged PTT Differential Drug/Disease Lab Patterns PT/aPTT Interpretation Logic Von Willebrand Disease Acquired VWD Syndrome

Screening Tool

The International Society on Thrombosis and Haemostasis (ISTH) Bleeding Assessment Tool (BAT) is used to screen for bleeding disorders.

Adult Males

Adult Females

Children

Board trap: the abnormal score cutoff is lowest in children (>2) and highest in adult females (>5) — don't apply a single universal cutoff across all three groups.

Platelet vs. Coagulation Disorder

Platelet Disorders (e.g., vWD, ITP)

Suspect with mucocutaneous bleeding — epistaxis, gum bleeding, easy bruising, menorrhagia, petechiae

Coagulation Disorders (e.g., hemophilia)

Suspect with spontaneous hemarthroses and muscle hematomas

Exam pearl: this single distinction — mucocutaneous bleeding = platelet problem; deep joint/muscle bleeding = coagulation factor problem — is one of the most efficient triage questions in all of bleeding-disorder medicine.

Medication Causes

Key rule: if bleeding symptoms or a low platelet count persist 10 days after discontinuation of a suspected offending medication, further evaluation for a bleeding disorder should be initiated — don't assume it's simply drug-related indefinitely.

Physical Examination

General: body habitus, hepatomegaly, hypermobility (consider connective tissue disorders like Ehlers-Danlos), jaundice, or splenomegaly
Skin/oral exam findings suggesting a bleeding disorder: truncal bruising, ≥5 bruises >1 cm in diameter, and atraumatic petechiae or hematomas
Signs of anemia

Board trap: the specific quantitative threshold — 5 or more bruises greater than 1 cm — is a concrete, testable exam finding pointing toward an underlying bleeding disorder rather than incidental trauma.

Differential Diagnosis — Causes of Prolonged PTT

Prolonged PTT, No Bleeding	Consider PT/INR (PTT Only)	Consider Both PTT and PT/INR
Early contact factor deficiency (Factor XII, HMWK, PK) Lupus anticoagulant Inappropriate blood draw Heparin contamination Erythrocytosis (laboratory artifact)	Hemophilia A and B Heparin Antiphospholipid antibody Intrinsic factor inhibitors (e.g., FVIII) Factor XI and XII deficiency	Warfarin Liver disease Risk factor for vitamin K deficiency (e.g., malabsorption, cholestasis, malnutrition) Suspected DIC Trauma patient / requiring massive transfusion protocol Bleeding patient Patient receiving thrombolytic therapy

Board trap: a prolonged PTT in a patient without any bleeding is often a laboratory artifact or a benign contact-factor deficiency (Factor XII, HMWK, PK) — these deficiencies do not cause clinical bleeding despite prolonging the PTT, a classic "don't overreact to the number" trap.

Drug/Disease Effects on Coagulation Labs

Disorder	PT	aPTT	Bleeding Time	Platelet Count
Warfarin	Prolonged	Normal	Normal	Normal
Aspirin	Normal	Normal	Prolonged	Normal
Heparin	Often normal (may be prolonged)	Prolonged	Normal	Normal
DIC	Prolonged	Prolonged	Prolonged	Low

Exam pearl: DIC is the only one of these four that drops the platelet count — warfarin, aspirin, and heparin all leave the platelet count normal despite affecting other parameters. Aspirin uniquely prolongs bleeding time only (platelet function defect), while sparing PT/aPTT entirely.

Laboratory Investigation & PT/aPTT Logic

Initial workup: CBC, peripheral blood smear, coagulation studies, and von Willebrand factor testing in females
Normal PT and aPTT may indicate a platelet disorder (coagulation cascade is intact; the problem is platelet number/function)
Normal PT + prolonged aPTT → disorder of the intrinsic coagulation pathway
Prolonged PT + normal aPTT → disorder of the extrinsic coagulation pathway
A low platelet count should be confirmed by recollecting the blood in a citrated or heparinized tube (to rule out pseudo-thrombocytopenia)

Exam pearl: memorize the pathway pairing — "PTT = intrinsic" and "PT = extrinsic." An isolated prolonged aPTT points to intrinsic pathway factors (VIII, IX, XI, XII); an isolated prolonged PT points to the extrinsic pathway (factor VII) — classically the earliest abnormality in vitamin K deficiency/warfarin effect.

Von Willebrand Disease (VWD)

Causes & Types

Most cases are autosomal dominant, causing reduced, dysfunctional, or absent von Willebrand factor.

Type	Description	Frequency
Type 1	Reduced VWF	Most common
Type 2	Dysfunctional VWF (4 subtypes)	Second most common
Type 3	Absent/undetectable VWF	Rare (most severe)

Clinical Presentation

Increased mucocutaneous bleeding, heavy menses, excessive postpartum bleeding
Joint and muscle bleeding are NOT typical — but can be seen specifically with types 2N and 3

Board trap: VWD is fundamentally a platelet-type/mucocutaneous bleeding disorder — but the exception (hemarthrosis-like bleeding in types 2N and 3) is specifically because these subtypes cause a secondary deficiency of factor VIII (VWF normally stabilizes/carries factor VIII), mimicking hemophilia-like bleeding.

Investigation

Normal CBC
Normal coagulation studies overall
aPTT may be prolonged if factor VIII is low (since VWF stabilizes factor VIII)
Confirmatory: VWF antigen (VWF:Ag) and platelet-dependent VWF activity

VWF:Ag Level	Interpretation
<30%	Confirms VWD
30–50%	Retest
>50%	Normal level

Exam pearl: memorize the exact VWF:Ag cutoffs — <30% confirms, 30–50% retest, >50% normal. This gray zone (30–50%) requiring retesting is a classic testable nuance rather than a simple binary cutoff.

When to Consider VWD

Individuals with bleeding (especially mucocutaneous), positive family history, mild thrombocytopenia, unexplained prolonged aPTT, or apparent hemophilia A.

Board trap: "apparent hemophilia A" on this list is important — since VWD can secondarily lower factor VIII, it can be mistaken for hemophilia A; always consider VWD in a patient who looks like they have hemophilia A but with a milder or atypical (mucocutaneous) bleeding pattern.

Education / Family Screening

First-degree relatives should have a thorough bleeding history and may require testing — particularly if they have a positive bleeding history or when the index patient has moderate to severe disease.

Management

1. Desmopressin (DDAVP)

Effective for Type 1 with minor bleeding

2. VWF Concentrate

For minor bleeding or surgery if DDAVP cannot be used or fails to control bleeding

3. Antifibrinolytics (Tranexamic Acid)

Especially effective in areas with naturally high fibrinolytic activity: nose, oropharynx, urogenital tract

Exam pearl: DDAVP is specifically most useful for Type 1 VWD — it works by releasing stored VWF from endothelial cells, which is less effective in Type 2 (dysfunctional VWF) or Type 3 (absent VWF), where VWF concentrate becomes the mainstay instead.

Acquired Von Willebrand Syndrome (AVWS)

Mechanism: includes autoantibodies to VWF
Major causes: lymphoproliferative disorders, myeloproliferative disorders, autoimmune disorders, cardiovascular conditions with vessel stenosis or high flow, left ventricular assist device (LVAD), and hypothyroidism
May be suspected in a patient with a recognized associated underlying condition, or with new-onset unexplained bleeding and no personal or family history of bleeding

Board trap: the key differentiator from inherited VWD is the absence of a personal/family bleeding history combined with a new onset — AVWS is acquired, often in the setting of a specific underlying condition (e.g., LVAD, myeloproliferative disease, hypothyroidism), not a lifelong pattern.