Diagnostic Procedures Flashcards

A 58-year-old male with type 2 diabetes presents with an HbA1c of 7.4% but his fasting plasma glucose readings at home consistently show values between 9.0–11.0 mmol/L. Which condition BEST explains this discrepancy?

Answer: Hemolytic anemia causing falsely low HbA1c

Hemolytic anemia reduces RBC lifespan, meaning fewer red blood cells are exposed to glucose for the full 120-day period. This leads to a falsely LOW HbA1c relative to actual glycemic control. The patient's home glucose readings of 9–11 mmol/L are more reflective of true hyperglycemia. Clinicians should use fructosamine or continuous glucose monitoring in patients with hemolytic conditions.

A pharmacist reviews a serum creatinine of 88 µmol/L in a 75-year-old female (weight 48 kg, height 162 cm) with suspected early renal impairment. Using the Cockcroft-Gault equation, which statement is MOST accurate when applying this result for drug dosing?

Answer: Lean body weight should be used, and the normal creatinine likely underestimates her true degree of renal impairment

In elderly, low-muscle-mass patients, serum creatinine can appear falsely 'normal' because creatinine production is reduced alongside muscle loss. The Cockcroft-Gault equation uses lean body weight (LBW) for underweight patients, and in this frail 75-year-old female, the seemingly normal creatinine masks a significantly reduced GFR. Relying on serum creatinine alone without calculating CrCl using correct weight would lead to drug overdosing.

A patient on long-term amiodarone therapy has TSH = 0.08 mIU/L and free T4 = 28 pmol/L (elevated). However, free T3 is LOW at 2.8 pmol/L. Which diagnostic interpretation is MOST correct?

Answer: Amiodarone's inhibition of T4-to-T3 conversion causing a non-pathological biochemical pattern

Amiodarone inhibits type 1 deiodinase, blocking peripheral conversion of T4 to T3. This results in characteristically elevated free T4, low/low-normal free T3, and transiently suppressed TSH — without true hyperthyroidism. This pattern is expected in the first few months of amiodarone therapy and should not be misinterpreted as amiodarone-induced thyrotoxicosis (AIT), which requires clinical symptoms and additional investigation (e.g., thyroid ultrasound, radioactive iodine uptake).

When interpreting a positive D-dimer result in a 67-year-old post-surgical patient being evaluated for DVT, which statement BEST reflects the clinical utility of this test in this context?

Answer: D-dimer has poor specificity post-surgery; a negative result is more clinically useful for ruling out DVT

D-dimer is a highly sensitive but poorly specific test. In post-surgical patients, D-dimer is almost universally elevated due to fibrinolysis from surgical trauma, rendering a positive result diagnostically useless. However, a NEGATIVE D-dimer still effectively rules out DVT/PE in low pre-test probability patients (high negative predictive value). The key diagnostic principle is that D-dimer is a 'rule-out' test, not a 'rule-in' test, especially in high-background-noise clinical contexts.

A patient's serum calcium is reported as 2.85 mmol/L (elevated). Serum albumin is 28 g/L (low). After correcting for albumin, the adjusted calcium is 2.62 mmol/L (normal). What is the MOST appropriate next diagnostic step for this patient?

Answer: Order ionized calcium to confirm true calcium status

When corrected calcium (using the standard albumin correction formula) falls within the normal range, true calcium status remains uncertain because the correction formula is an approximation. Ionized (free) calcium is the physiologically active fraction and the gold standard for assessing true calcium status, particularly in patients with hypoalbuminemia, acid-base disturbances, or critical illness. This directly determines whether treatment is needed, rather than acting on a calculated estimate.

A 44-year-old woman with recurrent UTIs has a urine culture growing E. coli at 10³ CFU/mL with symptoms of dysuria and frequency. The lab flags the result as 'insignificant growth.' Which action by the pharmacist is MOST appropriate?

Answer: Recognize that in symptomatic women, colony counts as low as 10² CFU/mL of a uropathogen can be clinically significant

The traditional threshold of ≥10⁵ CFU/mL was established for asymptomatic screening in women. Current evidence and Canadian guidelines recognize that in SYMPTOMATIC women with acute cystitis, colony counts as low as 10²–10³ CFU/mL of a recognized uropathogen (e.g., E. coli, Staphylococcus saprophyticus) are clinically significant and warrant treatment. Relying solely on the 10⁵ threshold in symptomatic patients leads to under-treatment.