CBC Interpretation - 30 MCQs

SECTION 1: Red Cell Parameters & Anemia Classification (Q1-Q10)

• A) Anemia of chronic disease
• B) Iron deficiency anemia
• C) Beta-thalassemia trait
• D) Sideroblastic anemia

• A) Iron deficiency anemia
• B) Beta-thalassemia trait
• C) Alpha-thalassemia trait (2-gene deletion)
• D) Hemoglobin E trait

• A) MCHC = (Hb / MCV) × 100
• B) MCHC = (Hb / Hct) × 100
• C) MCH = Hb × RBC
• D) Hct = Hb × 10

• A) Serum ferritin and TIBC
• B) Serum B12 and folate levels
• C) Hemoglobin electrophoresis
• D) Bone marrow biopsy

• A) Adequate compensatory erythropoiesis
• B) Hypoproliferative (aregenerative) anemia
• C) Hemolytic anemia
• D) Active hemorrhage with bone marrow response

• A) Iron deficiency anemia
• B) Anemia of chronic disease
• C) Mixed iron deficiency and ACD
• D) Sideroblastic anemia

• A) Shortened RBC lifespan
• B) Decreased erythropoietin production
• C) Iron sequestration by hepcidin
• D) Folate depletion from dialysis

• A) Average red cell size
• B) Degree of anisocytosis (variation in RBC size)
• C) Average hemoglobin content per cell
• D) Ratio of packed cells to whole blood

• A) Decreased Hb
• B) Decreased MCV
• C) Elevated RDW
• D) Decreased MCHC

• A) Megaloblastic anemia
• B) Diamond-Blackfan anemia
• C) Physiologic anemia of infancy
• D) Hemolytic disease of the newborn

SECTION 2: White Cell Parameters (Q11-Q18)

• A) Acute lymphoblastic leukemia
• B) Infectious mononucleosis (EBV)
• C) CMV mononucleosis
• D) Pertussis

• A) CLL
• B) ALL
• C) Bordetella pertussis (whooping cough)
• D) EBV infection

• A) WBC >20 × 10⁹/L
• B) Left shift (>10% band neutrophils)
• C) Toxic granulation in neutrophils on smear
• D) Leukopenia (<4 × 10⁹/L)

• A) Increased neutrophil production in bone marrow
• B) Demargination of neutrophils from vessel walls + decreased apoptosis
• C) Decreased neutrophil migration to tissues
• D) Both B and C

• A) ANC <1500/mcL
• B) ANC <1000/mcL
• C) ANC <500/mcL
• D) ANC <200/mcL

• A) Allergic rhinitis
• B) Tissue-invasive helminthic infection
• C) Drug reaction
• D) Atopic dermatitis

• A) Acute bacterial pneumonia
• B) Systemic lupus erythematosus with lymphopenia
• C) Viral infection (e.g., influenza)
• D) Parasitic infection

• A) Lead poisoning
• B) Female sex (Barr body in neutrophils)
• C) Pelger-Huet anomaly
• D) Hypersegmentation

SECTION 3: Platelet Parameters (Q19-Q23)

• A) Immune thrombocytopenic purpura (ITP)
• B) Gestational thrombocytopenia
• C) HELLP syndrome
• D) TTP

• A) Post-transfusion purpura
• B) Heparin-induced thrombocytopenia type II (HIT)
• C) Drug-induced ITP
• D) Disseminated intravascular coagulation

• A) Decreased TPO clearance
• B) Thrombopoietin shares homology with EPO and both are upregulated
• C) Cytokines (IL-6, IL-1) from chronic inflammation stimulate megakaryopoiesis
• D) Compensatory splenomegaly releases platelet stores

• A) Aplastic anemia
• B) Immune thrombocytopenic purpura (ITP)
• C) Myelosuppressive chemotherapy
• D) Hypersplenism

• A) <50 × 10⁹/L
• B) <20 × 10⁹/L
• C) <10 × 10⁹/L
• D) <5 × 10⁹/L

SECTION 4: Integrated CBC Interpretation & Clinical Scenarios (Q24-30)

• A) Acute lymphoblastic leukemia
• B) Chronic lymphocytic leukemia (CLL)
• C) Lymphoma in leukemic phase
• D) Reactive lymphocytosis

• A) Disseminated intravascular coagulation (DIC)
• B) Thrombotic thrombocytopenic purpura (TTP)
• C) Megaloblastic anemia
• D) Evans syndrome

• A) TTP
• B) HIT
• C) DIC
• D) Sepsis-associated thrombocytopenia

• A) Polycythemia vera
• B) Secondary polycythemia from hypoxia
• C) Relative polycythemia (Gaisbock syndrome)
• D) Essential thrombocythemia with erythrocytosis

• A) Low Hb, low reticulocytes, elevated LDH, elevated indirect bilirubin
• B) Low Hb, elevated reticulocytes, elevated LDH, elevated indirect bilirubin, low haptoglobin
• C) Low Hb, elevated reticulocytes, normal LDH, elevated direct bilirubin
• D) Low Hb, low reticulocytes, low LDH, low bilirubin

• A) Target cells
• B) Howell-Jolly bodies
• C) Siderocytes (Pappenheimer bodies)
• D) Acanthocytes

• A) Drug-induced hemolytic anemia
• B) Warm autoimmune hemolytic anemia (AIHA) with Evans syndrome
• C) Microangiopathic hemolytic anemia
• D) TTP

Quick Reference: CBC Normal Ranges

TB Screening in Schools: Step-by-Step & Real-Life Guide

Part 1: Why TB Screening in Schools Matters

1. Identify latent TB infection (LTBI) - infected individuals who are not yet sick but carry the bacteria
2. Detect active TB disease before it spreads
3. Provide preventive treatment to those at risk of progression
4. Perform contact investigation after any confirmed case

From Goldman-Cecil Medicine: "Testing of household contacts of patients with pulmonary TB is an important aspect of preventing TB and central to infection control programs." This principle extends directly to school settings where contact is prolonged and close.

Part 2: Understanding the Two Targets

Part 3: Testing Tools - What to Use

1. Tuberculin Skin Test (TST / Mantoux Test)

• How: 0.1 mL of purified protein derivative (PPD, 5 TU) injected intradermally into the volar forearm
• Read: 48-72 hours after injection - measure the induration (not redness) in mm
• Interpretation (standard cut-offs):

• Limitation in schools: BCG vaccination (given at birth in many countries) causes false-positive TST. This is a major practical issue in South Asia, Africa, and Southeast Asia where BCG is routine.
• A positive TST means T-cell immunity to TB antigens - it does NOT distinguish LTBI from active disease.

2. Interferon-Gamma Release Assays (IGRA)

• QuantiFERON-TB Gold Plus (QFT-Plus) - blood test
• T-SPOT.TB - blood test

• Not affected by BCG vaccination (uses ESAT-6 and CFP-10 antigens absent in BCG)
• Single visit (no return needed at 48-72 hrs)
• More specific - false-positive rates are uncommon (Robbins Pathology)

From Robbins & Kumar: "IGRAs are in vitro tests in which lymphocytes from the patient are stimulated with protein antigens from M. tuberculosis. Production of IFN-γ by the T cells is measured to assess the level of T-cell immunity... False-positive results are uncommon with IGRAs."

• In low-burden, BCG-vaccinated populations (most of South Asia, Africa): IGRA preferred to avoid false positives
• In resource-limited settings where IGRA is not affordable: TST remains the standard
• Both TST and IGRA cannot differentiate LTBI from active disease on their own

Part 4: Step-by-Step School Screening Protocol

STEP 1 - Identify Who Gets Screened (Risk Stratification)

• Born in or traveled to a high-burden TB country (South Asia, sub-Saharan Africa, Southeast Asia)?
• Household contact of a known TB patient in the last 2 years?
• HIV positive or on immunosuppressive therapy (steroids, biologics)?
• History of prior TB treatment or positive TST/IGRA?
• Lives in crowded housing, shelter, or correctional facility?
• Healthcare worker in a TB-endemic setting?
• Age <5 years (highest risk of progression to disease)?

STEP 2 - Obtain Informed Consent / Parental Consent

• Written consent from parent/guardian for minors
• Explain: purpose of the test, what a positive result means, that a positive TST/IGRA does NOT mean the child is sick
• Address common fears: "Will my child be removed from school?" (answer: not for LTBI alone)
• Ensure confidentiality - results should only be shared with parents, the student's doctor, and public health authorities per local law

STEP 3 - Perform the Test

1. Trained nurse/health worker draws up 0.1 mL PPD (5 TU/0.1 mL)
2. Clean volar forearm with alcohol, allow to dry
3. Hold skin taut, insert needle bevel-up at 10-15° angle
4. Inject to produce a 7-10 mm bleb (pale, raised wheal)
5. Do NOT bandage or rub the site
6. Record site, lot number, and date
7. Student returns in 48-72 hours for reading (no earlier, no later)

• Use ruler/calipers across the induration (NOT erythema/redness)
• Record mm of induration in the school health record
• A positive result requires follow-up - it does NOT diagnose TB disease

• Blood draw (venous) by trained phlebotomist
• Send to laboratory within 16 hours of collection
• Results available in 24-48 hours

STEP 4 - Classify and Triage Results

TST/IGRA RESULT
│
├── NEGATIVE → No further action (if no recent exposure)
│              Repeat in 8-10 weeks if recent exposure (<8 weeks) - "window period"
│
└── POSITIVE → Move to clinical evaluation (Step 5)

STEP 5 - Clinical Evaluation of Positive Tests

• Symptoms: cough >2 weeks, fever, night sweats, weight loss, fatigue, poor appetite
• Recent TB exposures
• Prior BCG vaccination (relevant for TST interpretation)
• Immune status (HIV, steroids, etc.)

• Anterior-posterior view (PA in older children)
• Look for: hilar lymphadenopathy (primary TB), apical infiltrates, cavitation, pleural effusion, calcified Ghon complex

STEP 6 - Workup for Suspected Active TB

• Sputum AFB smear and culture (children may need gastric lavage if they cannot produce sputum)
• GeneXpert MTB/RIF (Xpert) PCR test - identifies TB AND rifampin resistance within 2 hours
• Three sputum samples on consecutive days
• Culture on solid media: growth in 3-6 weeks; liquid media (MGIT): results in ~2 weeks
• Full drug susceptibility testing

From Robbins & Kumar: "PCR assays are as sensitive as culture in acid-fast smear-positive samples, but slightly less sensitive in smear-negative tuberculosis, and substantially less sensitive in children." This is a critical point - negative PCR does NOT rule out TB in a child.

STEP 7 - Treatment

LTBI treatment reduces risk of developing active TB by 75 to 90% (Goldman-Cecil Medicine).

• RIPE regimen: Rifampin + Isoniazid + Pyrazinamide + Ethambutol for 2 months, then Rifampin + Isoniazid for 4 more months
• Children <5 years in contact with smear-positive TB: treat empirically with preventive therapy even if tests are negative
• Directly Observed Therapy (DOT) strongly recommended

STEP 8 - Contact Investigation After a Confirmed Case

1. Identify contacts: All students/staff sharing the same classroom for prolonged periods (typically >8 hours cumulative exposure in high-burden settings; >1 hour in low-burden settings)
2. Concentric circle approach: Start with closest contacts (same class), expand if positivity rate is high
3. Notify public health authorities - mandatory reporting in virtually all countries
4. Test all contacts with TST or IGRA
5. Exclude the index case from school until:
   • Sputum smear converts to negative (usually after 2-3 weeks of effective treatment)
   • Clinical improvement demonstrated
   • Public health clearance given
6. School environment: Improve ventilation, ensure adequate air exchange; consider HEPA filtration in poorly ventilated classrooms

STEP 9 - Documentation and Follow-Up

• Record all tests, readings, referrals, and outcomes in the school health register
• Students on LTBI treatment: monthly follow-up for adherence and side effects (LFTs if symptoms, hepatotoxicity monitoring for INH)
• Repeat testing in future years if exposure risk persists
• BCG vaccination status should be documented for TST interpretation

Part 5: Real-Life Practical Challenges and Solutions

Part 6: Special Situations

Children <5 years of age

• Highest risk of progression from LTBI to active TB (including TB meningitis and miliary TB)
• Even with negative TST/IGRA, treat empirically if there is known close contact with smear-positive index case
• BCG vaccination at birth provides good protection against severe TB (miliary, meningitis) in young children but not reliable against pulmonary TB in older children and adults

HIV-Positive Students

• Annual TST/IGRA screening recommended regardless of prior results
• Higher risk of false-negative tests due to anergy
• Lower TST threshold (≥5 mm considered positive)
• Higher risk of progression and extrapulmonary TB

Students on Immunosuppressants (steroids, biologics for autoimmune diseases)

• Screen BEFORE starting immunosuppressive therapy
• TST/IGRA may be falsely negative while on treatment
• These students need LTBI treatment before starting anti-TNF agents (e.g., infliximab)

Summary Flowchart

ALL STUDENTS
     │
     ▼
RISK ASSESSMENT QUESTIONNAIRE
     │
     ├─ LOW RISK → No testing (or universal testing per local policy)
     │
     └─ HIGH RISK ↓
          │
          ▼
     TST or IGRA
          │
     ┌────┴────┐
  NEGATIVE   POSITIVE
     │           │
  Reassure    CXR + Clinical Exam
  (repeat if       │
  recent       ┌───┴───┐
  exposure)  LTBI   Active TB
               │        │
           Preventive  RIPE Regimen
           Therapy   + Public Health
           (3HP/4R/6H)  Notification
                      + Contact Tracing