STP Clinical Sciences 2

Question 1

A patient presents with elevated serum calcium, suppressed PTH, and elevated PTHrP. Which underlying condition is most likely?

Accepted Answer

Humoral hypercalcemia of malignancy

Answer

Elevated PTHrP with suppressed PTH and hypercalcemia is the hallmark of humoral hypercalcemia of malignancy, most commonly from squamous cell carcinomas.

Question 2

Which enzyme deficiency in the complement pathway results in recurrent Neisseria infections due to impaired membrane attack complex formation?

Accepted Answer

Terminal complement (C5-C9) deficiency

Answer

Deficiencies in terminal complement components (C5-C9) prevent formation of the membrane attack complex, specifically impairing defense against encapsulated Gram-negative organisms like Neisseria.

Question 3

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?

Accepted Answer

Folate deficiency

Answer

Elevated homocysteine with normal methylmalonic acid indicates folate deficiency, since methylmalonic acid is elevated only in B12 deficiency, not folate deficiency.

Question 4

In flow cytometry-based diagnosis of paroxysmal nocturnal hemoglobinuria (PNH), which surface markers are characteristically absent?

Accepted Answer

CD55 and CD59

Answer

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.

Question 5

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?

Accepted Answer

90%

Answer

Sensitivity = TP / (TP + FN) = 90 / (90 + 10) = 90%, representing the assay's ability to correctly identify true disease cases.

(STP) Scientist Training Programme Practice Test

(STP) Scientist Training Programme Practice Test

STP Clinical Sciences 2