Transcription
Hey, welcome to my channel, Medicosis Perfectio Alice. We have a series on hematology and oncology, so make sure to check that playlist.
In the previous video, we talked about alkaline phosphatase. Today's topic is leukocyte alkaline phosphatase. So let's get started. [Music]
In case you missed it, the topic of the previous video was alkaline phosphatase. Make sure to watch that previous video first, then come back to this video if you'd like to know what's going on.
I love etymology and terminology. Leukocyte alkaline phosphatase—let's break that down:
-ase: enzyme
phosphatase: an enzyme that removes phosphate groups from molecules; i.e., it causes dephosphorylation
alkaline: because it's stable and works best in an alkaline medium
leukocyte alkaline phosphatase: because we are talking about an enzyme in the leukocytes or white blood cells.
Okay, this enzyme, alkaline phosphatase, is present in almost every single tissue, but today's topic is specifically the one inside the white blood cells, particularly the mature white blood cells. This is very important. We have talked about this in the previous video. As you know, phosphate fixes stuff, so dephosphorylation—well, alkaline phosphatase will remove the phosphate so that the molecule can freely move into the cell.
Alkaline phosphatase in many tissues, including the white blood cells. And from the previous video, you know that high levels of alkaline phosphatase are seen in leukemoid reaction, but low levels of alkaline phosphatase are seen in chronic myeloid leukemia (CML). We will discuss leukemoid reaction in a future video, but for now, please know that leukemoid reaction is an exaggerated leukocyte response against a microbial pathogen. Usually, the leukocyte count will be greater than 50,000.
Okay, how do I know that this is not leukemia? This is the topic of today's video, because leukemia is a malignancy arising from marrow stem cells. Leukemia white blood cells can range anywhere from 10,000 all the way up to 100,000 or even more. So 50,000 or like 60,000 can be either a leukemoid reaction or a leukemia. How to know which is which? We need the leukocyte alkaline phosphatase. Leukemoid reaction is not cancer; leukemia, of course, is cancer. And your glorious leukocyte alkaline phosphatase score will tell you which is leukemia and which is leukemoid.
And don't forget, leukocyte alkaline phosphatase is found in mature white blood cells. As you know, CML has cells that are more mature than those in AML. AML is very immature; they have blasts with the famous Auer rods. But CML, they are more mature, but they are not as mature as the normal white blood cells; of course, they are still cancer. And in cancer, you have something called left shifting. What is left shift? Imagine that your hematopoietic stem cell is here, and your mature cell is here, and this is the hematopoiesis, as you know, goes from left, which is immature, to the right, which is the mature. So this is the stem cell, and this is the mature neutrophil. The normal growth goes like this. When you have something called left shifting, it means that you are having more immature cells than normal. In cancer, especially in acute leukemias, there is left shift. Of course, in chronic myeloid leukemia, there is still left shifting because the cells aren't mature enough to be as a normal white blood cell.
And also remember, I've told you in leukemia, the cells lose their ability to differentiate but retain their ability to replicate. I love this phrase: They lose their ability to differentiate but retain their ability to replicate. Isn't that interesting?
This glorious enzyme named alkaline phosphatase—we measure it through a process called the scoring method, or LAP score. If white blood cells are doing their job and they are mature, we will have high leukocyte alkaline phosphatase score, because mature granulocytes will uptake the stain for ALP into their cytoplasm. So we have high LAP score. But if white blood cells are useless and less mature, such as in cancer, maybe like chronic myeloid leukemia, you will have low LAP score. The cells are immature; they cannot uptake the stain for ALP into their cytoplasm as much as these mature cells can.
One more time: CML cells are, yes, more mature than AML, yet they are not as mature as normal white blood cells, because in leukemia, by definition, the cells lose their ability to differentiate but retain their ability to replicate. That's why leukemoid reaction will have high LAP score because the cells are mature; CML, low LAP score, the cells are less mature than normal—left shifting.
LAP can be high in case of leukemoid reaction, of course, as well as polycythemia vera, what we'll talk about in a later video. A LAP score is low in CML, as you know, cells are less mature than in leukemoid reaction. In aplastic anemia, of course, why? There is pancytopenia. There is pancytopenia; there is decreased white blood cells. You will have less white blood cells, then you will have less mature white blood cells. Pernicious anemia, of course, you can have also pancytopenia and pernicious anemia, and then you will have less white blood cells available, so the number of mature white blood cells are decreased.
Let's try to answer this vignette: 63-year-old female with notably high neutrophil count on CBC for a long time. She has been having this chronically. Today, she presents with splenomegaly on physical exam. This spleen is like, let's say, 10 centimeters below the left costal margin. You ordered bone marrow biopsy with cytogenetics to find a translocation between chromosomes 9 and 22. Which of the following findings are expected in lab investigation? TRAP positive, that is tartrate-resistant acid phosphatase; blasts greater than 50% of bone marrow; Auer rods; or low leukocyte alkaline phosphatase?
Please let me know the answer in the comment section, and I'll let you know in the next video. Until then, don't forget to subscribe, like me on Facebook, follow me on Soundcloud, don't forget to support me on Patreon. Go to www.patreon.com/medicosis to get more notes, more stuff, and early access to all of my videos. And you can tell me which video you would like me to produce in the future, and we'll make it happen. Medicosis Perfectio Alice—medicine should be fun.