Laboratory Medicine & Clinical Diagnostics Flashcards

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?

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.

A patient's HbA1c is reported as 8.5%. According to standard diabetes management guidelines, what does this value indicate?

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.

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:

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.

When collecting blood cultures from a patient with suspected bacteremia, which practice is MOST important to minimize contamination?

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.

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?

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.

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?

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.