What lab tests would you order to find the source of the problem?

Question

 Cushing's syndrome causes weight gain, excessive sweating, and muscle weakness. It can result from either the production of abnormally high levels of cortisol by the body, or overuse of glucocorticosteroid drugs. You are an endocrinologist working with a Cushing's syndrome patient. She is on hormonal birth control pills and takes an occasional ibuprofen.

A.  cortisol, LH, and FSH
B.  None -- the birth control pills include corticosteroid hormones. She should switch to another form of birth control.
C.  cortisol, ACTH, and CRH
D.  cortisol and ACTH

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

Gather Content
What do you already know about cortisol? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

C.  cortisol, ACTH, and CRH

Clarify Question
What is the key concept addressed by the question?
        · What lab tests would you perform for Cushing’s syndrome?
What type of thinking is required?
            o This is an analyze question because you have to examine each set of lab tests to see if it would be appropriate to find the source of the symptoms.

Gather Content
What do you already know about cortisol? What other information is related to the question?
        · As the question states, Cushing’s syndrome causes weight gain, excessive sweating, and muscle weakness and can be caused by high levels of cortisol. Adrenocorticotropic hormone (ACTH), produced by the anterior pituitary, stimulates the adrenal cortex to produce corticosteroid hormones including cortisol. These hormones are important in regulating glucose homeostasis and the body’s response to stress. ACTH is stimulated by corticotropin-releasing hormone (CRH) produced by the hypothalamus.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · As birth control pills usually contain analogs of estrogen and progesterone to regulate ovulation, they should not produce the effects aof Cushing’s syndrome. Similarly, LH and FSH are sex hormones that should not significantly influence Cushing’s syndrome. This syndrome is caused by excessive cortisol, so cortisol blood levels should be the first lab to be performed. As cortisol levels are regulated by ACTH and ACTH is stimulated via CRH, all three of these molecules would be appropriate to test to find the cause of the symptoms.

Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
       · Answering this question correctly depended upon evaluating each group of molecules as to its appropriateness in finding the cause of Cushing’s syndrome. If you got the answer correct, great! If not, which answer did you choose? Did you think that birth control pills contained corticosteroid hormones? They do include hormones (estrogen and progesterone), but not corticosteroids. Did you forget that CRH releases ACTH? Since both CRH and ACTH regulate cortisol, then testing all three of these molecules would be needed to find the source of the problem.