The Scattered Stethoscope

Sensitivity and specificity describe the test. Predictive values describe your patient. PPV answers the question they actually asked, which is that the test came back positive, so do they have it. NPV answers the other side, which is that the test came back negative, so are they in the clear.

Both move with prevalence, and that's what separates them from sensitivity and specificity. The same test performs differently depending on who's sitting in front of you, which is why a positive screening result in a low-risk population so often turns out to be nothing.

We build both on the same 2×2 table, walk through why reading across the rows answers a different question than reading down the columns, and go through the traps the exam builds around it.

The TCA cycle makes one GTP per turn, and it makes it at one step. This episode walks the whole wheel and shows what every step actually produces, so you can find that step instead of memorizing it.

For the brain that needs it different.

One blocked enzyme, two roads, and the lab pattern that tells you which one is closed.

This works the pathway on the board — methionine to SAM to SAH to homocysteine, and then the two things the body can do with homocysteine once it's there. When CBS is blocked, homocysteine piles up and methionine climbs with it, which is why a high homocysteine alone doesn't tell you anything and the methionine does.

Also covers how homocysteine damages fibrillin at the disulfide bonds, and why cysteine becomes an essential amino acid in these patients.

For the brain that needs it different.

Four findings and one lab that separate homocystinuria from Marfan.

Both give you a tall patient with long limbs, long fingers, and a dislocated lens, so you can't call it by looking. But the lens goes a different direction in each one, the joints go a different direction, and only one of them clots. This walks the four discriminators — lens, joints, brain, vessel — and then the lab pattern that confirms it.

Including why a high homocysteine alone doesn't tell you anything, and why the methionine is the number that does.

For the brain that needs it different.

Acid-base doesn't have to be memorized. In about fourteen minutes we build blood gas interpretation from scratch — two chemicals, two organs, and a method you can run on any ABG without a chart. No mnemonics, no memorized tables.

Anaphylaxis does two things to your blood vessels: wide and leaky. Everything else — the hives, the tight throat, the racing pulse, the eighty over forty — falls out of those two words. Plus why the swelling at the ankles is the missing blood pressure.

Back after a long break. I was sick, and getting better took longer than I planned. Thank you for waiting. This episode is the five causes of acute vision loss, and it starts with the one question that splits the differential in half before you look in the eye: is it painful or painless. Only one of the five hurts.

Is BMI real science? Do diets actually work? And why does losing weight so often feel like a fight you keep losing? This episode pulls apart the myths we've all been handed about weight, where that infamous number even came from, and why shame has never made anyone healthier. My husband sat in this time to bring his own point of view, and we go back and forth on the part that usually gets left out, that wanting to lose weight is completely fine, and it's the how that matters.

Diabetes is really just sugar ending up in the wrong places, so there isn't one drug for it. There's a drug for each place. This episode walks the whole body and picks up one tool at every stop. We start at the liver with metformin, the drug almost everyone gets first, then move to the fat and muscle with the glitazones, the pancreas with the sulfonylureas and meglitinides, the kidney with the SGLT2 inhibitors, and the gut with the alpha-glucosidase inhibitors. Then we finish with insulin itself, the one that replaces what's missing instead of nudging what's left. Every drug gets explained by the organ it works on, so the mechanisms, the side effects, and the reasons one gets chosen over another all follow from a single idea. Once you know the address, the drug explains itself.

Raw milk is having a moment. The current HHS Secretary drinks it, wants more people to have access to it, and the internet is full of claims about how it's more natural and better for you. So we went and checked. This one's about what the research actually says, why we started heating milk in the first place, and what the "good old days" leave out.