# Clinical Cases: Laboratory Medicine

## Case 1: Anemia Workup - Using the CBC and Peripheral Smear

### Patient Demographics
- **Age:** 45 years
- **Sex:** Female
- **Occupation:** Elementary school teacher

### Chief Complaint
"I've been feeling exhausted and short of breath when I climb stairs."

### History of Present Illness
A 45-year-old woman presents with progressive fatigue over 6 months. She initially attributed her tiredness to work stress but now notes she becomes short of breath walking up one flight of stairs. She reports occasional palpitations and lightheadedness. Her diet is unremarkable; she is not vegetarian. She has heavy menstrual periods (menorrhagia) lasting 7-8 days with frequent pad changes. She denies blood in stool, black stools, hematuria, or easy bruising. She has tried taking iron supplements intermittently but stopped due to constipation.

### Past Medical History
- Uterine fibroids (diagnosed 3 years ago)
- Menorrhagia
- No prior surgeries

### Medications
- Ibuprofen PRN for menstrual cramps
- Multivitamin (intermittent)

### Physical Examination
- **Vital Signs:** BP 118/72 mmHg, HR 98 bpm, RR 18/min
- **General:** Pale-appearing female, no acute distress
- **HEENT:** Pale conjunctivae; smooth, atrophic tongue (glossitis); angular cheilitis at mouth corners
- **Cardiovascular:** Tachycardic, regular rhythm, II/VI systolic flow murmur at LUSB
- **Nails:** Koilonychia (spoon-shaped nails)
- **Abdomen:** Soft, non-tender, no hepatosplenomegaly

### Laboratory Workup

**Complete Blood Count (CBC):**
| Parameter | Result | Reference Range | Interpretation |
|-----------|--------|-----------------|----------------|
| Hemoglobin | 8.2 g/dL | 12-16 g/dL | Low (anemia) |
| Hematocrit | 26% | 36-46% | Low |
| RBC Count | 3.8 million/mcL | 4.0-5.5 million/mcL | Low |
| **MCV** | 68 fL | 80-100 fL | **Low (microcytic)** |
| **MCH** | 22 pg | 27-33 pg | Low (hypochromic) |
| **MCHC** | 28 g/dL | 32-36 g/dL | Low |
| RDW | 18.5% | 11.5-14.5% | **Elevated (anisocytosis)** |
| WBC | 6,800/mcL | 4,500-11,000 | Normal |
| Platelets | 425,000/mcL | 150,000-400,000 | Mildly elevated (reactive) |

**Peripheral Blood Smear Findings:**
- **Microcytosis:** RBCs smaller than lymphocyte nuclei
- **Hypochromia:** Increased central pallor (>1/3 of cell diameter)
- **Anisocytosis:** Variation in RBC size (correlates with elevated RDW)
- **Poikilocytosis:** Abnormal shapes including:
  - Pencil cells (elongated elliptocytes)
  - Target cells (occasional)
- **Thrombocytosis:** Increased platelets (reactive to iron deficiency)

### Systematic Approach to Anemia

**Step 1: Classify by MCV**
- MCV 68 fL = **Microcytic anemia** (MCV < 80 fL)
- Differential for microcytic anemia:
  - **Iron deficiency** (most common worldwide)
  - Thalassemia
  - Anemia of chronic disease (can be microcytic)
  - Sideroblastic anemia
  - Lead poisoning

**Step 2: Order Iron Studies**

**Iron Studies:**
| Test | Result | Reference | Interpretation |
|------|--------|-----------|----------------|
| Serum Iron | 25 mcg/dL | 60-170 mcg/dL | **Low** |
| TIBC | 450 mcg/dL | 250-370 mcg/dL | **High** |
| Transferrin Saturation | 6% | 20-50% | **Very Low** |
| **Ferritin** | 8 ng/mL | 12-150 ng/mL | **Low (diagnostic)** |

**Iron Studies Interpretation:**

| Condition | Iron | TIBC | Ferritin | Saturation |
|-----------|------|------|----------|------------|
| **Iron Deficiency** | Low | High | **Low** | Low |
| Anemia of Chronic Disease | Low | Low-Normal | Normal-High | Low |
| Thalassemia Trait | Normal | Normal | Normal | Normal |
| Sideroblastic Anemia | High | Normal | High | High |

**Ferritin is the KEY differentiator:**
- Ferritin < 15 ng/mL is essentially diagnostic of iron deficiency
- Ferritin is an acute phase reactant - can be falsely normal/elevated with inflammation
- If inflammatory disease suspected, ferritin < 100 ng/mL with low transferrin saturation suggests iron deficiency

### Diagnosis
**Iron Deficiency Anemia** secondary to chronic blood loss (menorrhagia)

### Additional Workup
- **Reticulocyte count:** 0.8% (low for degree of anemia - inadequate marrow response due to iron deficiency)
- **Pelvic ultrasound:** Multiple uterine fibroids, largest 5 cm

### Why RDW is Elevated in Iron Deficiency
- RDW (Red Cell Distribution Width) measures variation in RBC size
- In iron deficiency: Mixed population of older normal-sized cells and newer microcytic cells
- This creates anisocytosis (elevated RDW)
- In contrast: Thalassemia trait has uniformly small cells with NORMAL RDW (helps differentiate)

### Clinical Findings Explained
| Finding | Pathophysiology |
|---------|-----------------|
| Glossitis (smooth tongue) | Rapidly dividing epithelial cells affected by iron deficiency |
| Angular cheilitis | Epithelial changes at mouth corners |
| Koilonychia (spoon nails) | Abnormal nail growth without adequate iron |
| Flow murmur | Hyperdynamic circulation compensating for anemia |
| Reactive thrombocytosis | Thrombopoietin cross-reacts with erythropoietin pathway |

### Treatment

**1. Iron Replacement:**
- **Ferrous sulfate 325 mg PO three times daily** (65 mg elemental iron per tablet)
- Take on empty stomach for best absorption (if tolerated)
- Take with vitamin C (orange juice) to enhance absorption
- Avoid taking with calcium, antacids, or proton pump inhibitors

**2. Address Underlying Cause:**
- Gynecology referral for fibroid management
- Consider GnRH agonists, hormonal therapy, or surgical options
- If GI blood loss suspected (especially in males or postmenopausal women): upper and lower endoscopy

**3. Monitoring:**
- Reticulocyte count in 1 week (should increase, indicating marrow response)
- Hemoglobin in 2-4 weeks (should increase 1-2 g/dL)
- Continue iron for 3-6 months AFTER hemoglobin normalizes to replete stores
- Recheck ferritin to confirm stores replete (goal > 50-100 ng/mL)

**If Oral Iron Not Tolerated or Ineffective:**
- IV iron (iron sucrose, ferric carboxymaltose, ferumoxytol)
- Consider if malabsorption (celiac disease, gastric bypass)
- Consider if ongoing losses exceed oral replacement capacity

### Clinical Pearl
The peripheral blood smear in iron deficiency shows microcytic, hypochromic red cells with increased central pallor, pencil cells, and elevated RDW reflecting anisocytosis. Ferritin is the most useful single test for diagnosing iron deficiency, but remember it's an acute phase reactant. The combination of low ferritin (<15), low serum iron, HIGH TIBC, and low transferrin saturation confirms iron deficiency. Always investigate the source of blood loss - in premenopausal women, menorrhagia is the most common cause; in men and postmenopausal women, GI blood loss must be excluded with endoscopy. The reticulocyte count should rise within 5-7 days of starting iron, and hemoglobin should increase by 1-2 g/dL within 2-4 weeks.

### Clinical Image
![Iron Deficiency Peripheral Smear](case_01_image.jpg)

*Peripheral blood smear demonstrating microcytic, hypochromic red blood cells characteristic of iron deficiency anemia. Note the increased central pallor (hypochromia) and the presence of pencil cells (elongated elliptocytes).*

**Image Source:** Wikimedia Commons - "Iron deficiency anemia blood smear"
**License:** CC BY-SA 3.0
**URL:** https://commons.wikimedia.org/wiki/File:Iron_deficiency_anemia_blood_smear.jpg

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## 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:**
| Test | Result | Reference Range | Interpretation |
|------|--------|-----------------|----------------|
| **PT** | 12.1 seconds | 11-14 seconds | **Normal** |
| INR | 1.0 | 0.8-1.2 | Normal |
| **PTT** | 58 seconds | 25-35 seconds | **Prolonged** |
| Platelet Count | 285,000/mcL | 150,000-400,000 | Normal |
| Bleeding Time | 4 minutes | 2-9 minutes | Normal |

### Systematic Approach to Prolonged PTT

**Step 1: Understand What PT and PTT Measure**

| Pathway | Test | Factors Assessed |
|---------|------|------------------|
| Extrinsic | PT | Factor VII (+ common pathway: X, V, II, fibrinogen) |
| Intrinsic | PTT | Factors XII, XI, IX, VIII (+ common pathway) |
| Common | Both | Factors X, V, II (prothrombin), I (fibrinogen) |

**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:**
| Condition | Result |
|-----------|--------|
| Immediate mix PTT | 32 seconds (corrected to normal) |
| Incubated mix (2 hours, 37C) | 34 seconds (remains corrected) |

**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:**
| Factor | Level | Reference Range |
|--------|-------|-----------------|
| Factor VIII | 85% | 50-150% |
| Factor IX | 78% | 50-150% |
| Factor XI | 82% | 50-150% |
| **Factor XII** | **< 5%** | 50-150% |

### 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

| Factor Deficiency | PTT | Bleeding Risk |
|-------------------|-----|---------------|
| Factor XII | Very prolonged | **NONE** |
| Prekallikrein | Prolonged | None |
| High-molecular-weight kininogen | Prolonged | None |
| Factor VIII (Hemophilia A) | Prolonged | **SEVERE** |
| Factor IX (Hemophilia B) | Prolonged | **SEVERE** |
| Factor XI | Prolonged | Variable (often mild) |

### 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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