We’ve talked about a whole bunch of different hemolytic anemias over the past few weeks.
We’ve gone through the main hereditary hemolytic anemias: hereditary spherocytosis (and its less-common counterpart, hereditary elliptocytosis), glucose-6-phosphate dehydrogenase deficiency, the hemoglobinopathies (like sickle cell anemia) and the thalassemias.
We’ve also talked about immune-related hemolytic anemia (warm and cold), which is an acquired hemolytic anemia.
The last main type of hemolytic anemia on our list is microangiopathic hemolytic anemia, or MAHA for short, which falls under the acquired group of hemolytic anemias. In this type of hemolytic anemia, the red cells are ripped apart by physical trauma. Often the trauma results from red cells getting snagged as they try to pass through vessels laden with fibrin strands (there are a ton of situations in which this occurs, as we’ll see). Sometimes the trauma is due to other types of trauma (like an artificial heart valve that busts a few red cells each time it closes).
Let’s take a look at the other-types-of-trauma group first because it’s a little easier to conceptualize. There are two main causes of MAHA in this group: artificial heart valves and coarctation of the aorta. They really should call this group “macroangiopathic hemolytic anemia” because the problem is in big (macro) not tiny (micro) vessels, but they didn’t ask me. In both of these causes, red cells are getting ripped up in large spaces – either by the smashing of cells within an artificial heart valve (the old ball-and-socket valves were the worst for this; the newer models are much kinder to red cells), or by the ripping apart of red cells in turbulent blood flow (as you would get in coarctation of the aorta).
The remaining cases of MAHA are due to red cells getting snagged as they try to traverse thrombus-laden vessels. There are tons of situations in which the patient starts forming fibrin at an increased rate. If you look at Robbins, or any hematology textbook, you’ll be quickly overwhelmed by the sheer number of disorders and conditions that are associated with a microangiopathic hemolytic anemia, such as:
The blood smear is where the action is in MAHA. If you look carefully at a blood smear from a patient with MAHA, you’ll see fragmented red cells, or schistocytes. Schistocytes are smaller than normal red cells, and they have points on them. There are all kinds of permutations on this theme – some schistocytes have just one point, some look like they have little horns, some just look like little ragged red cell shards. If you look at the image above, you’ll see a whole bunch of schistocytes of varying shapes.
The most specific type of schistocyte is the “triangulocyte” (that’s really the name; would I make that up?), which is, as the name suggests, a triangular fragment of a red cell. These aren’t as common as the other types of schistocytes (there isn’t a triangulocyte in the above image). If you see one of those puppies, you better figure out what’s going on with the patient.
And that’s the main point I want to make about this type of hemolytic anemia. Given all the causes of this anemia – many of which carry a high mortality – you can’t just say the patient has MAHA, and move on to the next blood smear. You have to figure out what’s causing the hemolysis (or, rather, the clinician needs to figure it out); don’t miss this one. It could be a matter of life and death.
Photo credit: Ed Uthman at http://commons.wikimedia.org/ (DIC_With_Microangiopathic_Hemolytic_Anemia_(301920983).jpg)
Here’s a good question about two entities that sound the same (but aren’t).
Q. What is the difference between heparin associated thrombocytopenia (HAT) and heparin induced thrombocytopenia (HIT)? (more…)
Here’s a nice boards – type question that requires you to put together some clinical and laboratory data to form a diagnosis, and then describe what the blood smear would look like. (more…)
Another great board-type review question, this time on coagulation and platelet tests: (more…)
Here’s a very good question about the diagnostic use of the bleeding time.
Q. I’m currently studying heme for boards and came across a practice questions that used platelet count, bleeding time, PT and PTT values to differentiate between certain diseases/problems. I was just wondering how in both Vitamin K deficiency and liver disease you can get an increase in PT and PTT but the bleeding time doesn’t change…I guess I figured that bleeding time would have to increase. Can you explain this to me?
A. Yeah, that does sound weird, you’d think the bleeding time would change – but actually, the bleeding time is only a measure of platelet function. It really has nothing to do with coagulation!
I kind of think of it like this: the platelet plug is the first thing to form, and that is enough to stop the bleeding from the incision made at the beginning of the test. The coagulation cascade happens next, and the status of that won’t be apparent in the bleeding time results. The patient might have some more bleeding later if their coagulation system is really screwed up…but the bleeding time assay will be done by then. In reality, it probably happens a little more concurrently than that (platelet plug is followed very closely by fibrin formation – the two probably even overlap a bit), but I think it’s a good way to remember the concept.
The same reasoning fits with the way that people with coagulation factor disorders bleed (as opposed to patients with platelet disorders). People with platelet abnormalities tend to bleed spontaneously into mucous membranes without much provocation (probably because they’re having a hard time forming that initial platelet plug) whereas patients with coagulation factor abnormalities, like hemophilia, tend to have deep, severe bleeds that happen after some time has elapsed (because they form the initial platelet plug okay, but they can’t seal it up with fibrin very well, so they end up bleeding later on).
Who names this stuff, anyway?!
Coagulation factors, for the most part, have two names: a Roman numeral name and an English wordy name. (more…)
Mapo doufu is an ancient Chinese dish that made me feel dizzy the first time I ate it. (more…)
Rudolf Virchow, a German pathologist in the 1800s, is considered by many to be “the father of pathology.” His famous Omnis cellula e cellula (“every cell originates from another existing cell like it”) theory, published in1858, rejected the then-prevalent belief that organisms could spontaneously arise from non-living matter (e.g., that maggots could spontaneously appear in decaying meat). (more…)
Queen Victoria reigned as British sovereign from 1837 until 1901. Britian enjoyed prosperity and growth under her monarchy, but her genetic legacy was another story. (more…)
Factor V Leiden is a genetic disorder in which patients have an increased tendency to form thromboses, or blood clots. (more…)
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