Haematology question - please help

[Phloston]

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From GT:

"A 17-year-old male who recently emigrated, with his family, from Cambodia presents in your clinic for continued management of his anemia. His peripheral smear is shown. A medical report indicates the presence of hemoglobin α2δ2. Which is the likely diagnosis?

A. Iron deficiency anemia
B. One deletion of the α-globin gene
C. Two deletions of the β-globin gene
D. Two deletions of the α-globin gene
E. Three deletions of the β-globin gene

Answer Explanation

The correct answer is D.

This patient has a hypochromic, microcytic anemia. Classically, the presence of HbA2 (α2δ2) suggests β-thalassemia minor. However, this is not one of the answer choices.

The learning point is that HbA2 is present in mild alpha-thalassemia – there's not enough of an alpha-chain deficiency to prevent the formation of HbA2. Hence, the correct answer is 2 deletions of the α-globin gene.

One α-globin deletion would not cause a microcytic anemia. Two deletions of the β-globin gene would cause beta-thalassemia major."

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Could someone please explain why in the world choice C is wrong.

I would think that you'd see increased HbA2 and HbF in beta-thalassaemia major, not just minor.

Cheers,

 

[usmlesuccess]

I am thinking that if he had beta thalassemia major, they would have put more information about his status. He would definitely have more problems than just an "anemia." Also I think his geography provides a clue. SE asian=alpha thal in usmle language..lol

 

[usmlesuccess]

also, whereas beta thalassemias usually involve decreased synthesis of the gene, alpha thal usually involves DELETIONS.

 

[frankyazz]

I would have to agree and say yes, you would see increased HbA2 in both major and minor. Although this seems like a tricky question, I would have to say clinical presentation is important. He's Asian, and Cooley's anemia is a severe hemolytic anemia. Also I'd imagine the blood smear to be important. Is there anything about the blood smear that makes you think it was Cooley's?

 

[Phloston]

I would have to agree and say yes, you would see increased HbA2 in both major and minor. Although this seems like a tricky question, I would have to say clinical presentation is important. He's Asian, and Cooley's anemia is a severe hemolytic anemia. Also I'd imagine the blood smear to be important. Is there anything about the blood smear that makes you think it was Cooley's?

The blood smear just showed typical target cells.

I understand the "learning point" that two alpha deletions could still yield the possibility for increased HbA2 and that him being Asian makes alpha, vs beta, more likely. I'm not questioning that.

I would just think HbA2 levels would, overall, be highest in Cooley's because there's no other way to compensate than to produce HbA2 and HbF (and epsilon and other less significant types), whereas in alpha thalassaemia trait (two deletions), although HbA2 is found, it wouldn't be nearly as abundant because HbA1 is still produced.

The only thing I can think of is that this question-writer was merely trying to emphasize the point that he's Asian and nothing else. Therefore, beta shouldn't even be considered, and that's the only alpha choice that's relevant.

 

[iCY]

The blood smear just showed typical target cells.

I understand the "learning point" that two alpha deletions could still yield the possibility for increased HbA2 and that him being Asian makes alpha, vs beta, more likely. I'm not questioning that.

I would just think HbA2 levels would, overall, be highest in Cooley's because there's no other way to compensate than to produce HbA2 and HbF (and epsilon and other less significant types), whereas in alpha thalassaemia trait (two deletions), although HbA2 is found, it wouldn't be nearly as abundant because HbA1 is still produced.

The only thing I can think of is that this question-writer was merely trying to emphasize the point that he's Asian and nothing else. Therefore, beta shouldn't even be considered, and that's the only alpha choice that's relevant.

by the way, keep in mind that GT tends to write horrible quesitons. Their program is better for recall & practice than for doing qbank questions. This kinda bs Q wouldn't show up on step 1 & the answers would be more straightforward

 

[Phloston]

by the way, keep in mind that GT tends to write horrible quesitons. Their program is better for recall & practice than for doing qbank questions. This kinda bs Q wouldn't show up on step 1 & the answers would be more straightforward

Nice, iCY. I would hope so.

And I've started to realize that about GT. Give or take though, USMLE Rx had some bad questions too, but GT has quite a few more. I still consider these GT questions valuable though because I have in fact picked up some details/things I've never encountered before, and that could always get me one or two (or more) questions on the real exam.