Clinical Sciences Flashcards
7 cards from real STP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Clinical Sciences flashcards as text
A patient presents with elevated serum calcium, suppressed PTH, and elevated PTHrP. Which underlying condition is most likely?
Answer: Humoral hypercalcemia of malignancy
Elevated PTHrP with suppressed PTH and hypercalcemia is the hallmark of humoral hypercalcemia of malignancy, most commonly from squamous cell carcinomas.
Which enzyme deficiency in the complement pathway results in recurrent Neisseria infections due to impaired membrane attack complex formation?
Answer: Terminal complement (C5-C9) deficiency
Deficiencies in terminal complement components (C5-C9) prevent formation of the membrane attack complex, specifically impairing defense against encapsulated Gram-negative organisms like Neisseria.
A 45-year-old woman has a hemoglobin of 7.2 g/dL, MCV 110 fL, and elevated homocysteine with normal methylmalonic acid. Which deficiency is most likely?
Answer: Folate deficiency
Elevated homocysteine with normal methylmalonic acid indicates folate deficiency, since methylmalonic acid is elevated only in B12 deficiency, not folate deficiency.
In flow cytometry-based diagnosis of paroxysmal nocturnal hemoglobinuria (PNH), which surface markers are characteristically absent?
Answer: CD55 and CD59
PNH is caused by a somatic PIG-A mutation leading to loss of GPI-anchored proteins CD55 (DAF) and CD59 (protectin), which normally protect red cells from complement lysis.
A clinical scientist is validating a new diagnostic assay. The assay identifies 90 true positives and 10 false negatives from 100 confirmed disease cases. What is the sensitivity?
Answer: 90%
Sensitivity = TP / (TP + FN) = 90 / (90 + 10) = 90%, representing the assay's ability to correctly identify true disease cases.
Which type of renal tubular acidosis (RTA) is associated with hypokalemia and inability to acidify urine below pH 5.5?
Answer: Type 1 (distal) RTA
Type 1 (distal) RTA is caused by failure of alpha-intercalated cells to secrete H+ in the collecting duct, resulting in inability to acidify urine below pH 5.5 and associated hypokalemia.
In Gram staining, which step differentiates Gram-positive from Gram-negative bacteria?
Answer: Decolorization with alcohol/acetone
Decolorization with alcohol or acetone is the critical differentiating step; Gram-positive organisms retain the crystal violet-iodine complex due to their thick peptidoglycan wall, while Gram-negative organisms are decolorized.