SPEAKER_00 0:00

You know, we all carry around this um this fundamental expectation when it comes to medicine.

SPEAKER_01 0:04

Aaron Powell Right. We want clear answers.

SPEAKER_00 0:06

Exactly. We want biology to fit into neat, tidy little boxes, like normal versus abnormal, healthy versus sick.

SPEAKER_01 0:15

Aaron Powell Yeah. A diagnosis should just be a light switch, right? It's either on or off.

SPEAKER_00 0:18

Aaron Ross Powell But human biology is famously I mean, it's almost aggressively messy.

SPEAKER_01 0:23

It really is.

SPEAKER_00 0:24

Imagine trying to categorize every single person in the world as either strictly tall or strictly short. Where do you even draw the line?

SPEAKER_01 0:34

Aaron Ross Powell Right. Like is it five foot nine? Sure.

SPEAKER_00 0:37

Say it's five foot nine. What happens to the person who is literally one millimeter below that line? Does their entire, you know, physical reality change?

SPEAKER_01 0:44

Aaron Powell It sounds like a purely philosophical riddle when you put it like that.

SPEAKER_00 0:48

Right.

SPEAKER_01 0:48

But for clinicians, drawing those lines across continuous biological spectrums, uh it's an everyday necessity.

SPEAKER_00 0:54

Aaron Powell You have to make a call.

SPEAKER_01 0:56

Exactly. You cannot prescribe a treatment for a millimeter of difference. You need a category. And where you fall relative to those clinical lines has massive real-world implications. It dictates your diagnosis, your treatment, and like your identity as a patient.

SPEAKER_00 1:13

Aaron Powell, which brings us to the core of what we're unpacking today in this deep dive.

SPEAKER_01 1:16

It's a fascinating topic.

SPEAKER_00 1:18

It really is. We're looking at an article by William Ayrd, a leading hematologist called The Evolution of Von Willebrand Disease Classification and Thresholds.

SPEAKER_01 1:26

Such a great paper.

SPEAKER_00 1:27

Yeah. And the mission for our deep dive today is to explore how doctors attempt to draw these rigid lines across a continuous biological spectrum.

SPEAKER_01 1:36

Because the history of naming and categorizing von Willebrand disease or VWD is really just the history of medical decision making itself.

SPEAKER_00 1:45

Okay, let's unpack this. Before we get into where the lines blur, we need to establish what the basic lines actually are.

SPEAKER_01 1:51

Right. The foundational classification of VWD.

SPEAKER_00 1:54

Right, which all revolves around this glycoprotein called von Willebrand factor. I like to think about it like a factory.

SPEAKER_01 1:59

Oh, the workplace analogy, yeah.

SPEAKER_00 2:00

Yeah. So think of the clotting process as a factory. Type one VWD is a factory with a worker shortage. The workers you have are fine, but there just aren't enough of them to get the job done.

SPEAKER_01 2:11

Aaron Powell A partial quantitative deficiency.

SPEAKER_00 2:13

Trevor Burrus Exactly. Then you have type two. Here you have plenty of workers on the floor, but they are doing the job wrong. They're dysfunctional.

SPEAKER_01 2:21

A qualitative dysfunction.

SPEAKER_00 2:23

And then type three just means the factory is completely abandoned. There's virtually complete deficiency.

SPEAKER_01 2:28

Aaron Powell It's a really solid analogy. And you know, making that division between quantity and quality was a massive conceptual leap in medicine.

SPEAKER_00 2:36

Aaron Powell Because before that, VWD was just what, a vague bleeding tendency?

SPEAKER_01 2:41

Aaron Powell Exactly. It stopped being this mysterious bleeding tendency and became a highly specific family of failure modes.

SPEAKER_00 2:47

Aaron Powell Oh, that makes sense.

SPEAKER_01 2:48

Trevor Burrus By tying the clinical categories directly to the mechanism like less protein versus abnormal protein clinicians could suddenly anticipate treatment needs.

SPEAKER_00 2:56

Aaron Powell Right. Because if you have a factory of workers doing the job wrong in type two, the immediate next question for a manager has to be, well, how exactly are they messing up?

SPEAKER_01 3:05

Aaron Powell And dysfunction just isn't specific enough when you're trying to stop a patient from hemorrhaging.

SPEAKER_00 3:10

Trevor Burrus Right. So the broad type 2 bucket was forced to split as the science got better.

SPEAKER_01 3:15

Aaron Powell Yeah. Through things like multi-meralysis and platelet binding studies.

SPEAKER_00 3:19

Aaron Powell So get 2A, 2B, 2M, and 2N.

SPEAKER_01 3:22

Aaron Powell What's fascinating here is that these subcategories weren't created just for like scientific elegance.

SPEAKER_00 3:28

Trevor Burrus They weren't just showing off.

SPEAKER_01 3:29

No, not at all. They were created because the mechanism dictates the consequence.

SPEAKER_00 3:34

Aaron Powell Let's break those down. So type 2A is the loss of large multimermers. The workers basically lack the physical reach to do their jobs.

SPEAKER_01 3:41

Aaron Powell Right, resulting in a frail clot.

SPEAKER_00 3:43

But then type 2B, this is where the VWF binds platelets way too avidly.

SPEAKER_01 3:48

It binds too aggressively, yeah.

SPEAKER_00 3:50

Wait, really? Because you'd think hyperbinding equals better clotting, right? Why is an overly sticky protein bad?

SPEAKER_01 3:58

Well, it spontaneously binds to platelets while just floating in the bloodstream. It sweeps them up into these useless clumps, and then the spleen clears them out.

SPEAKER_00 4:06

Oh wow. So you just burn through your platelet supply before you even get a cut?

SPEAKER_01 4:09

Precisely. Which means you need completely different treatment considerations for 2A versus 2B.

SPEAKER_00 4:16

That makes total sense. Yeah. Then we have 2M, which is impaired platelet function, but normal multimerants.

SPEAKER_01 4:21

Right.

SPEAKER_00 4:21

And finally 2N, where it has impaired factor 8 binding.

SPEAKER_01 4:25

This one is incredible because it looks clinically identical to mild hemophilia A.

SPEAKER_00 4:30

So it's basically mimicking a completely different disease.

SPEAKER_01 4:33

Yes. Because factor 8 deficiency is the mechanism of hemophilia A. You literally have to use specific VWF testing or genetic sequencing to tell them apart.

SPEAKER_00 4:43

Wow. Okay, so we've seen how complicated quality can get with type 2, but surely measuring quantity for type 1 is just simple math, right? You either have enough workers or you don't.

SPEAKER_01 4:53

You would think so, but this is where we hit the core threshold problem. VWF levels are continuously distributed.

SPEAKER_00 5:00

Like a bell curve.

SPEAKER_01 5:01

Exactly. And thresholds are just an attempt to convert a biological trait into a strict clinical category.

SPEAKER_00 5:07

Right, which brings up the massive historical gray area in the text. Well levels between 30 and 50 IUDL.

SPEAKER_01 5:12

Evan Sadler's framework is so helpful here. He showed that low VWF can act like two fundamentally different things.

SPEAKER_00 5:21

Depending on the level, right?

SPEAKER_01 5:22

Yeah. So below 30, it often functions like a true disease with clear heritability.

SPEAKER_00 5:27

Meaning it runs strongly in families.

SPEAKER_01 5:28

Right. But between 30 and 50, it often lacks clear genetic variance and actually correlates pretty poorly with real-world bleeding. It acts more like a mere risk factor.

SPEAKER_00 5:39

Aaron Powell Here's where it gets really interesting. In 2021, the major hematology organizations, ASH, ISTH, all of them, they released new guidelines.

SPEAKER_01 5:48

Huge shift in the field.

SPEAKER_00 5:50

They shifted patients who had abnormal bleeding and VWF levels below 50 from just having a low VWF label right into the official type 1 VWD category.

SPEAKER_01 5:59

They moved the biological goalposts.

SPEAKER_00 6:01

Wait, so they just moved the goalposts. I mean, are we medicalizing normal variations just so people can get insurance coverage?

SPEAKER_01 6:07

I know it sounds like that. And it was controversial. But it was prioritized to improve access to care and prevent misdiagnoses.

SPEAKER_00 6:14

Especially for women, right?

SPEAKER_01 6:15

Absolutely. Think about women with heavy menstrual bleeding or severe postpartum hemorrhages. The boundary might be scientific, but it's deeply practical.

SPEAKER_00 6:24

So the label effects of static care, procedure planning, all of that.

SPEAKER_01 6:28

Exactly. A label changes patient anxiety and it forces surgeons to take prophylactic measures seriously.

SPEAKER_00 6:34

Okay, I get the pragmatism. But if the 2021 guidelines show that medical labels can change over time, the source material reveals something even wilder.

SPEAKER_01 6:42

Oh, the shifting lab numbers.

SPEAKER_00 6:44

Yes. The patient's own lab numbers change over time too. VWF levels are not static at all.

SPEAKER_01 6:49

They are incredibly fluid.

SPEAKER_00 6:51

They rise with age, they're influenced by stress, inflammation, pregnancy.

SPEAKER_01 6:55

Even your ABO blood group. Type O naturally has much lower levels.

SPEAKER_00 6:59

Which creates this crazy clinical paradox. A child diagnosed with type 1, because their level is below 30, they might get retested in adulthood and fall into the 30-50 rate.

SPEAKER_01 7:10

Or even above 50, completely normalizing on paper.

SPEAKER_00 7:13

So wait, the disease didn't disappear, but the snapshot changed. The biological proof just evaporated.

SPEAKER_01 7:19

That's exactly it. A single VWF level is just a moment in time, not a verdict. Wow. Genetics really help clarify types two and three, but type one remains so heavily modified by environment and biology. A purely lab-based approach just fails.

SPEAKER_00 7:35

If we can't completely trust the lab numbers to stay still, what can we trust?

SPEAKER_01 7:40

We have to look at the actual patient's life experience.

SPEAKER_00 7:43

Right, the central role of the bleeding history.

SPEAKER_01 7:46

Which is why they introduced bleeding assessment tools or bets.

SPEAKER_00 7:49

Aaron Powell Because symptoms like easy bruising or heavy periods are totally subjective.

SPEAKER_01 7:55

Exactly. These tools try to standardize those vague symptoms into objective scores.

SPEAKER_00 8:00

Aaron Powell But the text is very clear about the severe limitations of these tools.

SPEAKER_01 8:03

They definitely have blind spots.

SPEAKER_00 8:05

Like a young boy who might have severe VWD, but he's never had a hemostatic challenge, like he's never had surgery or a tooth pulled.

SPEAKER_01 8:11

Right. His score would be artificially low.

SPEAKER_00 8:13

And then there's the cultural or familial blind spot. This blew my mind.

SPEAKER_01 8:17

It's a normalization of pathology.

SPEAKER_00 8:19

Yes. A woman from a family with VWD might severely underreport her heavy bleeding because she thinks it's perfectly normal.

SPEAKER_01 8:27

Because her mother and sister experience the exact same thing.

SPEAKER_00 8:30

If we connect this to the bigger picture.

SPEAKER_01 8:32

Well, if we connect this to the bigger picture, diagnosis absolutely requires a relational approach.

SPEAKER_00 8:38

Meaning you can't just look at one thing.

SPEAKER_01 8:40

Right. Labs, family history, and personal bleeding history, they all have to be weighed together. No single element is sovereign.

SPEAKER_00 8:48

So what does this all mean for you, the listener?

SPEAKER_01 8:51

It's a lot to take in.

SPEAKER_00 8:52

It is. I I think the takeaway is that VWD categories types one, two, and three, they are incredibly useful tools. They guide testing and they absolutely save lives.

SPEAKER_01 9:03

But they are interpretive tools. They are not rigid borders in nature.

SPEAKER_00 9:06

Aaron Powell Because classifying a continuous, context-dependent hemostatic system is always going to require human clinical judgment.

SPEAKER_01 9:14

Medicine has to draw lines. We need them to function. But good doctors know those lines are drawn in pencil.

SPEAKER_00 9:20

Drawn in pencil. I love that. And it leaves me with this final thought for you to chew on.

SPEAKER_01 9:25

What's that?

SPEAKER_00 9:25

Think about the actual psychological weight of a diagnostic label.

SPEAKER_01 9:29

Oh, that's a really good point.

SPEAKER_00 9:30

Right. Because if your VWF levels sit in that gray area, how does being officially labeled with a disease change the way you view your own fragility?

SPEAKER_01 9:40

It completely reframes your reality.

SPEAKER_00 9:42

Does the label make you feel broken? Or, you know, does it finally validate a lifetime of symptoms that people might have dismissed?

SPEAKER_01 9:50

Yeah, that validation is huge.

SPEAKER_00 9:52

Because sometimes the most powerful thing a classification system does isn't directing a treatment, it's changing the story you tell about yourself.

SPEAKER_01 9:59

I couldn't agree more.