NBME 23 Leukocyte alkaline phosphatase activity greater than 250 U/L (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 2/Question#24 (reveal difficulty score)
A 46-year-old woman has a 1-day history of ...
Leukocyte alkaline phosphatase activity greater than 250 U/L 🔍 / 📺 / 🌳 / 📖
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submitted by ∗vshummy(184)

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This question is word for word in First Aid 2019 page 424 under CML. -- I did't realize it was there until I got it wrong.

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vshummy "Very low leukocyte alkaline phosphatase (LAP) as a result of low activity in malignant neutrophils vs benign neutrophilia (leukemoid reaction) in which LAP is increased due to increased leukocyte count with neutrophilia in response to stressors (eg, infections, medications, severe hemorrhage)." +7

+3 upvote downvote
submitted by ∗paulkarr(73)

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Chronic Myelogenous Leukemia vs Leukemoid Reaction has a few differentiating features:

Basophilia can be seen in Myeloproliferative diseases such as CML. However, they are not seen in Leukemoid Reactions.
Leukocyte Alkaline Phosphatase (LAP) is often elevated in Leukemoid Reactions. But it will be decreased in CML because Abnormal cells don't make the normal enzyme.
Dohle Bodies are characteristic of Leukemoid Reactions. Not seen in CML.

As vshummy pointed out FA-2019 pg 424 has all this information as well as UWorld problem...I just can't seem to find the Q.ID. Maybe someone else can tag-team in.

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thotcandy LAP 100-249 do not fall into the answer choice but would still be considered high value and thus +LAP to indicate leukemoid. A LAP- would be in the normal values which is 20-100, not below 250 like the answer choice indicates. +

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submitted by ∗aakb(41)

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can someone explain to me why 0% basophils is incorrect?

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chaosawaits My best understanding is that in a leukemoid reaction, the basophils would still be within the normal reference range, but greater than zero, say 0.5%. In essence, there would be some basophils, not absolutely zero basophils that 0% implies. Seems pedantic to me, but that's how I'm taking it. +

+2 upvote downvote
submitted by ∗nlkrueger(51)

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why isn't, "0% blasts on the peripheral smear" right? is this the distinguishing future for acute leukemia?

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lispectedwumbologist Because you'll see some blast cells in a leukemoid reaction. It won't be 0%. +9

paulkarr Also, don't get confused with 0% Basophils. Basophils are seen in CML but not in Leukemoid reactions. I just went with LAP because they pointed it out in the lab values. Had that not been there, I would have chosen "0% basophils" +1

usmile1 the "left shift" you see in leukomoid reaction actually is describing the increase in immature leukocytes on CBC. that is why the LAP is important to be able to distinguish them +1

+1 upvote downvote
submitted by ∗imnotarobotbut(184)

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Pathoma says there are 3 things that differentiate leukemoid from CML: + Leukocyte alkaline phosphatase (only in leukemoid) + Basophils (only in CML) + t(9;22) translocation (only in CML)

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nor16 yeah but pathoma doesnt help here... +2

thotcandy Yeah but LAP is normally 20-100 so a 100-250 U/L is still + which would indicate Leukemoid reaction, no? That's why I didn't pick it, Because I figured 250 u/l was just some random number and it didn't make sense. a -LAP would be in the normal range, 20-100 which would THEN indicate CML. +1

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