Laboratory Approach to Diagnose a Male Child with Repeated Joint Bleeding (Hemarthrosis)

Brief Pathology

• Hemophilia A - Factor VIII deficiency (incidence: 1 in 5,000 live male births)
• Hemophilia B (Christmas disease) - Factor IX deficiency (incidence: 1 in 30,000 males)

Step-by-Step Laboratory Approach

Step 1: Initial Screening Tests

Key pattern: Isolated prolonged aPTT with normal PT and normal platelet count = intrinsic pathway factor deficiency.

Step 2: aPTT Mixing Studies

• Correction of aPTT → suggests a factor deficiency (missing factor is supplied by normal plasma)
• No correction → suggests an inhibitor (e.g., lupus anticoagulant or an acquired factor inhibitor)

Important nuance: Factor VIII inhibitors are time-dependent. An immediate mix may correct, but a 1-hour incubated mix will show prolongation. Always run both immediate and incubated mixing studies.

Step 3: Specific Factor Assays (Confirmatory)

Step 4: Severity Classification (Factor VIII or IX level)

Step 5: Distinguish from Von Willebrand Disease (vWD)

The VWF:VIII binding assay distinguishes type 2N vWD from hemophilia A but is only available at specialized labs. In a male child with no female relatives affected, X-linked hemophilia A is far more likely than type 2N vWD.

Step 6: One-Stage vs. Two-Stage / Chromogenic Assay

• The standard one-stage clot-based aPTT assay is used most commonly.
• A two-stage or chromogenic factor VIII assay may give discrepant (lower) results in mild discrepant hemophilia A, where up to 40% of mild cases are missed by the one-stage assay alone.
• The World Federation of Hemophilia recommends performing both at initial diagnosis.

Step 7: Inhibitor Detection (if treatment fails)

• Repeat aPTT: prolonged
• Mixing study: no correction (inhibitor pattern)
• Bethesda assay: quantifies inhibitor titer in Bethesda Units (BU/mL)
  • < 5 BU/mL = low-titer inhibitor (may still respond to high-dose factor)
  • ≥ 5 BU/mL = high-titer inhibitor (requires bypassing agents: rFVIIa or aPCC)

Step 8: Genetic / Molecular Testing

• Identifies the specific F8 or F9 gene mutation
• Useful for carrier detection in female relatives and prenatal diagnosis
• A family history may be absent in up to 30% of infant males with hemophilia A (spontaneous mutations)

Diagnostic Algorithm Summary

Male child + recurrent hemarthrosis
        ↓
 Screening: CBC, PT, aPTT, TT, Bleeding time
        ↓
 Isolated ↑ aPTT, normal PT, normal platelets
        ↓
 aPTT Mixing Study
    ↙           ↘
Corrects       No correction
(Deficiency)   (Inhibitor → Bethesda assay)
    ↓
Measure Factor VIII, IX, XI activities
    ↙              ↘
Low FVIII         Low FIX
(normal IX/XI)    (normal VIII/XI)
    ↓                  ↓
Hemophilia A      Hemophilia B
    ↓
Severity classification
+ vWD workup if needed
+ Molecular testing

• Tietz Textbook of Laboratory Medicine, 7th Edition - Inherited Coagulation Disorders, Factor VIII & Factor IX Deficiency sections (pp. 3122-3124)
• Goldman-Cecil Medicine - Hemophilia and Arthritis chapter (p. Hemophilia section)

Laboratory Diagnosis of Repeated Joint Bleeding (Hemarthrosis) in a Male Child

Pathology (Brief)

• Hemophilia A - Factor VIII deficiency (1 in 5,000 male births)
• Hemophilia B (Christmas disease) - Factor IX deficiency (1 in 30,000 males)

1. Acute synovitis - blood in the joint space triggers an inflammatory response
2. Iron deposition - repeated bleeds deposit hemosiderin in the synovium, stimulating synoviocyte proliferation
3. Chronic proliferative synovitis - the hypertrophied synovium becomes a source of further bleeding
4. Cartilage degradation - proteolytic enzymes from activated synoviocytes destroy articular cartilage
5. End-stage hemophilic arthropathy - bone enlargement, crepitus, muscle atrophy, joint contractures, and complete loss of joint space

Laboratory Approach: Step by Step

Step 1 - Initial Screening Tests

Step 2 - aPTT Mixing Study

Important: Factor VIII inhibitors are time-dependent. An immediate mix may falsely correct. Always run an incubated (1-hour at 37°C) mixing study alongside the immediate mix to detect time-dependent inhibitors.

Step 3 - Specific Factor Assays (Confirmatory)

Contact factors (XII, prekallikrein, HMWK) also prolong aPTT but do not cause clinical bleeding - they are excluded by the clinical context of hemarthrosis.

Step 4 - Severity Classification

Step 5 - Exclude Von Willebrand Disease (vWD)

Step 6 - One-Stage vs. Chromogenic Assay

• The one-stage clot-based aPTT assay is standard.
• A chromogenic (two-stage) Factor VIII assay may give discrepant (lower) results in mild discrepant Hemophilia A - up to 40% of mild cases can be missed by one-stage assay alone.
• The World Federation of Hemophilia recommends performing both at the time of initial diagnosis.

Step 7 - Inhibitor Detection (if factor replacement fails)

• aPTT remains prolonged despite treatment
• Mixing study: no correction (inhibitor present)
• Bethesda Assay: quantifies inhibitor titer in Bethesda Units (BU/mL)

Step 8 - Molecular / Genetic Testing

• Identifies the specific F8 or F9 gene mutation
• Used for carrier detection in female relatives
• Used for prenatal diagnosis in subsequent pregnancies
• Important note: up to 30% of Hemophilia A cases arise from de novo spontaneous mutations - absence of family history does not exclude the diagnosis

Summary Diagnostic Algorithm

Male child + recurrent hemarthrosis
              ↓
   CBC, PT, aPTT, TT, Bleeding time
              ↓
Isolated prolonged aPTT
Normal PT, Normal platelets, Normal bleeding time
              ↓
        aPTT Mixing Study
       ↙                  ↘
  Corrects             No correction
 (Deficiency)            (Inhibitor)
       ↓                     ↓
Measure F VIII, F IX,    Bethesda Assay
F XI activities          (quantify inhibitor)
   ↙         ↘
Low F VIII   Low F IX
= Hemophilia A  = Hemophilia B
       ↓
Severity by activity level
+ vWD workup if needed
+ One-stage AND chromogenic assay
+ Molecular testing

• Tietz Textbook of Laboratory Medicine, 7th Ed. - Inherited Coagulation Disorders; Factor VIII Deficiency (Hemophilia A); Factor IX Deficiency (Hemophilia B) (pp. 3122-3124)
• Goldman-Cecil Medicine - Hemophilia and associated arthropathy

Cigarette Smoking and Squamous Cell Carcinoma of the Lung

Pathology (Brief)

Gross Pathology

Histopathology

• Intercellular bridges (desmosomes between squamous cells)
• Individual cell keratinization (bright pink cytoplasm)
• Keratin pearls - concentric whorls of keratinizing squamous cells (hallmark of well-differentiated SCC)
• Nuclear pleomorphism, hyperchromasia, and mitotic figures
• Ranges from well-differentiated (abundant keratin) to poorly differentiated (squamous features minimal or absent)

Squamous cell carcinoma of the lung. A: intercellular bridges. B: keratin pearl (arrow) and individual cell keratinization (arrowheads). C: p40 IHC (nuclear brown staining) confirming squamous differentiation. - Murray & Nadel's Respiratory Medicine / Robbins Basic Pathology

Immunohistochemistry

• p63 / p40 - nuclear positive (hallmark of squamous differentiation)
• TTF-1 and Napsin A - negative (distinguishes from adenocarcinoma)
• CK5/6 - positive

The Smoking-SCC Correlation: Step by Step

1. Epidemiology

• ~80% of all lung cancers occur in active smokers or recent ex-smokers
• SCC is the lung cancer subtype most tightly linked to tobacco - it is rare in never-smokers
• Risk is 60 times greater in heavy smokers (2 packs/day for 20 years) vs. nonsmokers
• Incidence correlates nearly linearly with pack-years
• SCC accounts for approximately 25% of all lung cancers in the United States
• Historically up to two-thirds of SCC presented as central hilar tumors; peripheral SCC has increased with the shift to filtered cigarettes

2. Carcinogens in Cigarette Smoke

3. "Field Cancerization" Effect

• Chromosome deletions at 3p, 9p (CDKN2A locus), and 17p (TP53 locus) are detectable in histologically normal bronchial epithelium of smokers - long before any visible tumor
• This "field effect" explains why multiple synchronous or metachronous lung cancers can arise, and why former smokers retain elevated risk even after cessation
• Genetic changes can persist for many years in bronchial epithelium after quitting smoking

4. Stepwise Progression: The Metaplasia-Dysplasia-Carcinoma Sequence

Normal pseudostratified
ciliated columnar epithelium
         ↓  (smoke → chronic irritation)
Goblet cell hyperplasia
         ↓
Basal cell (reserve cell) hyperplasia
         ↓
Squamous metaplasia
(normal columnar epithelium replaced by stratified squamous epithelium)
         ↓
Squamous dysplasia
(disordered squamous epithelium: loss of polarity, nuclear hyperchromasia,
pleomorphism, mitoses, increased N:C ratio)
         ↓  (Mild → Moderate → Severe dysplasia)
Carcinoma in situ (CIS)
(full-thickness cytologic atypia; basement membrane intact)
         ↓
Invasive Squamous Cell Carcinoma
(basement membrane breached; invasion into stroma and lymphovascular channels)

The squamous carcinogenesis sequence in smoking-damaged bronchial epithelium. A: goblet cell hyperplasia. B: basal cell hyperplasia. C: squamous metaplasia. D: squamous dysplasia. E: carcinoma in situ. F: invasive SCC. - Robbins Basic Pathology

5. Molecular/Genetic Events (SCC-Specific)

Key contrast: Unlike adenocarcinoma (which has actionable EGFR, ALK, ROS1 mutations), SCC mutations are currently not actionable for targeted therapy. Treatment relies on immunotherapy (PD-L1 targeting) and chemotherapy.

6. Why Squamous Cell and Not Adenocarcinoma?

7. Other Risk Modifiers

• Secondhand smoke: Contains the same carcinogens; ~3,000 nonsmoker lung cancer deaths/year in the US
• Industrial co-carcinogens: Asbestos (especially with smoking - synergistic, not additive), arsenic, chromium, nickel, uranium - all amplify SCC risk
• Radon gas: Radioactive decay produces alpha-particle-emitting isotopes that cause direct DNA strand breaks in bronchial epithelium
• Genetic susceptibility: P-450 polymorphisms and DNA repair gene variants (mutagen sensitivity genotype) confer >10-fold higher risk in smokers vs. controls with the same exposure
• Cessation: Reduces risk over time but never returns to baseline due to persisting epigenetic and genetic changes in the field-mutagenized epithelium

• Robbins & Cotran Pathologic Basis of Disease - Etiology and Pathogenesis of Lung Cancer; Acquired Mutations (pp. 668-670)
• Robbins & Kumar Basic Pathology - Morphology and Carcinogenesis sequence (pp. 486-488)
• Murray & Nadel's Textbook of Respiratory Medicine - Squamous Cell Carcinoma (p. 562)