Which of the following blood tests should be performed before a blood transfusion?

Correct Answer: B

Rationale: Before administering a blood transfusion, it is crucial to perform blood typing and cross-matching to ensure compatibility between the donor's blood and the recipient's blood. This process helps prevent adverse reactions such as transfusion reactions, which can be life-threatening. Prothrombin and coagulation time, bleeding and clotting time, as well as CBC and electrolyte levels are important tests in other clinical contexts, but for blood transfusions, blood typing and cross-matching are essential to ensure patient safety.

Correct Answer: D

Rationale: The correct answer is D (25,000/mm³) because leukocytosis is clinically defined as a white blood cell (WBC) count significantly higher than the normal range, which typically spans **4,500–11,000/mm³** in adults. A count of 25,000/mm³ is **well above this upper limit**, strongly indicating an abnormal proliferation of WBCs, often due to infections (e.g., bacterial), inflammatory conditions, leukemia, or severe stress. This level of elevation is unambiguous and requires immediate clinical investigation. **Why the other choices are incorrect:** - **A (4,500/mm³):** This falls at the **lower end of the normal range** (4,500–11,000/mm³) and does not suggest leukocytosis. In fact, it could indicate leukopenia (low WBC count) if it were any lower, but at this value, it is simply within the normal spectrum. - **B (7,000/mm³):** This is **squarely within the normal range** and represents a healthy WBC count. While minor fluctuations can occur due to factors like exercise or mild infections, this value does not raise clinical concern for leukocytosis. - **C (10,000/mm³):** Although this is at the **upper threshold of normal**, it does not definitively indicate leukocytosis. Some individuals may have baseline WBC counts near this level without pathology. Only persistent or markedly elevated counts (typically >11,000/mm³) are diagnostically significant. **Key distinctions:** - **Normal vs. Abnormal:** Leukocytosis requires a clear deviation from the reference range. While slight elevations (e.g., 10,500/mm³) may sometimes be labeled as leukocytosis in clinical contexts, **25,000/mm³ is unequivocally pathological**. - **Clinical Context Matters:** Stress, medications, or pregnancy can cause mild WBC increases, but extreme counts (like 25,000/mm³) often point to severe infections (e.g., sepsis), hematologic disorders, or tissue damage. - **Differential Diagnosis:** Lower values (A–C) might not warrant intervention, whereas D demands further tests (e.g., peripheral smear, differential count) to identify the underlying cause. This explanation underscores the importance of understanding both the numerical thresholds and the clinical implications of WBC counts in diagnosing leukocytosis.

Correct Answer: A

Rationale: The symptoms of fatigue, muscle cramping, and muscle weakness in a patient after starting furosemide therapy are indicative of hypokalemia. Furosemide is a loop diuretic that can lead to potassium depletion, causing hypokalemia. Hypokalemia can manifest with muscle weakness, cramps, and fatigue due to alterations in neuromuscular function and decreased ATP production.

Correct Answer: A

Rationale: The correct answer is A because there are contraindications for chest X-rays, such as pregnancy or concerns about radiation exposure. Patients may need to remove jewelry and metallic objects to prevent interference with the imaging. While a signed consent is typically not required for a routine chest X-ray, there are specific situations where consent may be necessary. It is essential for patients to follow fasting instructions before certain types of chest X-rays to obtain accurate results.

Correct Answer: A

Rationale: The correct answer is A (Early in the morning) because sputum accumulation is naturally highest after a night of sleep due to prolonged stasis of respiratory secretions, which allows for a more concentrated and representative sample of pulmonary flora or pathogens. Overnight, mucus pools in the airways, increasing the yield of microorganisms for culture. This timing also minimizes contamination from food particles or oral flora, which can interfere with accurate diagnostic results. Morning collection ensures optimal specimen quality for detecting infections like tuberculosis or bacterial pneumonia, where diagnostic sensitivity depends on adequate bacterial load. Choice B (After the patient eats a light breakfast) is incorrect because eating introduces food debris and oral bacteria into the mouth and throat, contaminating the sputum sample. Salivary dilution and the mechanical action of chewing/swallowing reduce the concentration of lower respiratory secretions, leading to false-negative cultures or misidentification of commensal flora as pathogens. Additionally, postprandial collection may trigger gagging or vomiting, further compromising specimen integrity. Choice C (After aerosol therapy) is incorrect because nebulized medications (e.g., bronchodilators or saline) dilute sputum and alter its composition, washing away pathogens or distorting microbial concentrations. Aerosols also increase salivary contamination, making it harder to distinguish between upper and lower respiratory tract organisms. For accurate cultures, specimens should be collected *before* aerosol treatments to avoid therapeutic interference. Choice D (After chest physiotherapy) is incorrect because percussion or postural drainage mobilizes secretions from smaller airways, but these techniques often mix sputum with saliva and oropharyngeal contaminants. While physiotherapy may increase sputum volume, it does not guarantee a representative sample from the lungs. Furthermore, the mechanical disruption can fragment bacterial colonies, reducing culture sensitivity. Early morning collection without prior intervention remains the gold standard. In summary, morning sputum collection maximizes diagnostic accuracy by leveraging physiological secretion retention, minimizing contamination, and avoiding iatrogenic interference. The other choices introduce variables that compromise specimen quality, leading to unreliable microbiological results.