NBME 16 -didnt find explanation any explanation yet

[zeevee]

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1) one of the questions is about a neonate born with PDA but the description of PDA is " continuous machine like murmur along left sternal border , increased precordial activity and bounding peripheral pulses "
Answer was simple just asking about indomethacin .

Is it typical for PDA to have that location and description of murmur .Why are there AR signs here .

2) A question is about iron deficiency anemia .Hb is 8.2g/dl , hematocrit is 25% and MCV is 69%.The reticulocyte count is 0.8% .Isnt this a normal reticulocytes count ?( 0.5-1.5% N) while it shouldnt be .
Which anemias has low reticulocyte count ?

Got it correct in the exam because nothing else suited but still looking for the explanation

3) 67 year old comes for routine examination.Her brother and mother had colon cancer.She only allows FOBT .The physician explains that FOBT is not appropriate in her case because of
a) low sensitivity ( correct answer)
b) low specificity
c) uncertain PPV
d) uncertain NPV

isnt FOBT a high sensitivity test and that is why it is a screening test .All screening tests should be sensitive

 

[Phloston]

1) one of the questions is about a neonate born with PDA but the description of PDA is " continuous machine like murmur along left sternal border , increased precordial activity and bounding peripheral pulses "
Answer was simple just asking about indomethacin .

Is it typical for PDA to have that location and description of murmur .Why are there AR signs here .

2) A question is about iron deficiency anemia .Hb is 8.2g/dl , hematocrit is 25% and MCV is 69%.The reticulocyte count is 0.8% .Isnt this a normal reticulocytes count ?( 0.5-1.5% N) while it shouldnt be .
Which anemias has low reticulocyte count ?

Got it correct in the exam because nothing else suited but still looking for the explanation

3) 67 year old comes for routine examination.Her brother and mother had colon cancer.She only allows FOBT .The physician explains that FOBT is not appropriate in her case because of
a) low sensitivity ( correct answer)
b) low specificity
c) uncertain PPV
d) uncertain NPV

isnt FOBT a high sensitivity test and that is why it is a screening test .All screening tests should be sensitive

1) Lesson from clinical practice is murmurs can be heard anywhere. You could hear an aortic stenosis by all means in the axilla if it's a loud one. But on boards it's second intercostal on the right sternal border with radiation to the carotids. To answer your question though, that's fair game for PDA, as is above the clavicle. Could also be described as "to-and-fro" or "pan-systolic-pan-diastolic"; both = continuous, machinery-like.

2) Reticulocyte count can be variable. If it's high you think acute blood loss in conjunction with healthy bone marrow. If it's low you think the BM isn't producing adequately (e.g., aplastic anaemias, chemotherapy, B9/B12 deficiencies). Iron deficiency can definitely lead to decreased reticulocyte count. But it doesn't have to be low if anaemia is not chronic or severe.

3) FOBC isn't sensitive because you'll get many false-negatives. (TP/TP+FN). Not all cancer bleeds, so you know you'll have false-negatives with FOBC. Colonoscopy would be most sensitive. On that note, FOBC isn't specific either cuz lots of things can cause bleeding (e.g., diverticular disease, angiodysplasia, polyps, etc.).

 

[zeevee]

Thankyou

 

[worldbeater]

Just some extra points to add to what the poster above said:
(1)

Is it typical for PDA to have that location and description of murmur .Why are there AR signs here .

"Machine like murmur" is a classic clue for PDA

(2)

A question is about iron deficiency anemia .Hb is 8.2g/dl , hematocrit is 25% and MCV is 69%.The reticulocyte count is 0.8% .Isnt this a normal reticulocytes count ?( 0.5-1.5% N) while it shouldnt be .
Which anemias has low reticulocyte count ?

Your MCV is less than 70, so it is microcytic anemia. If they didn't give you iron deficiency, your options are:

Fe deficiency, anemia of chronic disease, sideroblastic, thalassemia, lead poisoning, sickle cell "FAST LeadS"

If your reticulocyte is high, in addition to acute blood loss you can think of something that is "chewing up" the RBCs, like a metal valve or something lysing the RBCs. Schistocytes would be present in this case.

(3)

3) FOBC isn't sensitive because you'll get many false-negatives. (TP/TP+FN)

Ah, it's the FN that's screwing up the sensitivity, thanks for putting in the equation, makes more sense now. I was thinking about sensitivity being "SPIN in"/ruling in, that wasn't helping with this particular question.

 

[Phloston]

Just some extra points to add to what the poster above said:
(1)
"Machine like murmur" is a classic clue for PDA

(2)
Your MCV is less than 70, so it is microcytic anemia. If they didn't give you iron deficiency, your options are:

Fe deficiency, anemia of chronic disease, sideroblastic, thalassemia, lead poisoning, sickle cell "FAST LeadS"

If your reticulocyte is high, in addition to acute blood loss you can think of something that is "chewing up" the RBCs, like a metal valve or something lysing the RBCs. Schistocytes would be present in this case.

(3)
Ah, it's the FN that's screwing up the sensitivity, thanks for putting in the equation, makes more sense now. I was thinking about sensitivity being "SPIN in"/ruling in, that wasn't helping with this particular question.

Sensitivity rules out, specificity in. Typo?

 

[worldbeater]

Yeah, thanks for catching it.