DHA Laboratory Medicine & Clinical Diagnostics — Questions and Answers
Question 1: A patient on warfarin therapy for atrial fibrillation has an INR of 5.8 with no active bleeding. What is the MOST appropriate initial management?
- Administer intravenous vitamin K 10 mg immediately
- Hold warfarin and monitor; administer oral vitamin K 1–2.5 mg if needed (Correct answer)
- Give fresh frozen plasma (FFP) urgently
- Continue warfarin at the same dose and recheck in 1 week
Correct answer: Hold warfarin and monitor; administer oral vitamin K 1–2.5 mg if needed
For supratherapeutic INR (4.5–10) with no active bleeding, guidelines recommend holding warfarin and administering low-dose oral vitamin K (1–2.5 mg). High-dose IV vitamin K risks over-correction causing warfarin resistance. FFP is reserved for active bleeding or urgent surgery.
Question 2: A patient's HbA1c is reported as 8.5%. According to standard diabetes management guidelines, what does this value indicate?
- Average blood glucose of approximately 197 mg/dL over the past 2–3 months (Correct answer)
- Average blood glucose of approximately 126 mg/dL — at the diagnostic threshold
- Average blood glucose of approximately 240 mg/dL over the past 2–3 months
- Normal glycemic control — target achieved
Correct answer: Average blood glucose of approximately 197 mg/dL over the past 2–3 months
HbA1c 8.5% corresponds to an estimated average glucose (eAG) of approximately 197 mg/dL. The formula is: eAG = 28.7 × HbA1c − 46.7. Most diabetic management targets are HbA1c < 7% (eAG ~154 mg/dL), so 8.5% indicates suboptimal control.
Question 3: A patient presents 4 hours after chest pain onset. Troponin I is elevated at 2.8 ng/mL (upper reference limit 0.04 ng/mL). ECG shows ST elevation in V1–V4. The CORRECT interpretation is:
- Elevated troponin confirms heart failure — start diuresis
- ST-elevation myocardial infarction (STEMI) — activate cath lab immediately (Correct answer)
- Result is a false positive; troponin rises only after 12 hours
- Unstable angina — admit for observation and serial ECGs only
Correct answer: ST-elevation myocardial infarction (STEMI) — activate cath lab immediately
ST elevation in anterior leads (V1–V4) combined with significantly elevated troponin I is diagnostic of STEMI. Current guidelines mandate immediate reperfusion (primary PCI) within 90 minutes of first medical contact. Troponin begins rising within 3–6 hours of myocardial injury.
Question 4: When collecting blood cultures from a patient with suspected bacteremia, which practice is MOST important to minimize contamination?
- Collect samples immediately after antibiotic administration
- Use the same venipuncture site for all bottles to minimize patient discomfort
- Disinfect the venipuncture site with chlorhexidine or alcohol and allow it to fully dry before puncture (Correct answer)
- Collect only one set of blood cultures to reduce volume drawn
Correct answer: Disinfect the venipuncture site with chlorhexidine or alcohol and allow it to fully dry before puncture
Proper skin antisepsis (chlorhexidine ≥0.5% or 70% isopropyl alcohol) and allowing complete drying before venipuncture is the single most important step to prevent contamination. Cultures should ideally be collected before antibiotics, from separate sites, and at least 2 sets obtained.
Question 5: A complete blood count (CBC) shows: WBC 1.8 × 10⁹/L, Hgb 7.2 g/dL, Platelets 45 × 10⁹/L. This pattern of pancytopenia MOST suggests which underlying condition?
- Iron deficiency anemia
- Polycythemia vera
- Bone marrow failure or infiltration (e.g., aplastic anemia, leukemia) (Correct answer)
- Dehydration with hemoconcentration
Correct answer: Bone marrow failure or infiltration (e.g., aplastic anemia, leukemia)
Pancytopenia (low WBC, Hgb, and platelets simultaneously) indicates a problem at the level of bone marrow production or infiltration — causes include aplastic anemia, leukemia, myelodysplastic syndrome, or marrow infiltration by cancer. Iron deficiency causes only anemia; polycythemia increases cell counts; dehydration increases concentrations.
Question 6: A urinalysis shows: specific gravity 1.030, pH 5.0, protein 2+, glucose 3+, nitrites positive, leukocyte esterase positive, RBC 10–15/hpf. Which combination of findings MOST strongly suggests urinary tract infection WITH underlying diabetes?
- Specific gravity 1.030 and pH 5.0
- Protein 2+ and RBC 10–15/hpf
- Glucose 3+ combined with nitrites positive and leukocyte esterase positive (Correct answer)
- High specific gravity and low pH alone
Correct answer: Glucose 3+ combined with nitrites positive and leukocyte esterase positive
Glycosuria (glucose 3+) without hyperglycemic symptoms can indicate diabetes or a low renal threshold. Positive nitrites (bacterial nitrate reduction) and leukocyte esterase (pyuria marker) together are specific for bacterial UTI. The combination of glycosuria + UTI markers most strongly points to UTI in a diabetic patient.
DHA Laboratory Medicine & Clinical Diagnostics
A patient on warfarin therapy for atrial fibrillation has an INR of 5.8 with no active bleeding.
What is the MOST appropriate initial management?