The three-times-upper-limit convention, and where it came from
Asymptomatic pancreatic enzyme elevation is common on treatment and is not pancreatitis. The distinction is clinical, not biochemical.
Laboratory Notebook
Page 11 of 12 of this archive, newest first.
Page 11
Equal area is not equal mass: the response factor problem
Peptide bonds absorb strongly near 214 nm; aromatic side chains absorb near 280 nm. A method reading at 280 is blind to any fragment lacking an aromatic residue.
Gauge, pain and flow rate
Skin thickness at the standard injection sites is approximately two millimetres in adults and varies remarkably little with body mass. That single finding is why short…
How a correct calculation becomes a wrong dose
Almost every case involves a change — a new vial, a new syringe size, a new supplier — carried forward with an old number.
HbA1c and its lag: what a result three months old is telling you
HbA1c integrates roughly three months of glycaemia with the most recent weeks weighted most heavily. Almost every misreading of it is a misreading of that weighting.
D-amino acids are invisible to mass spectrometry, and that is the whole problem
What would be needed to catch each of these, and what it would cost.
Site selection when the tissue has already changed
A rotation scheme that is too complicated will not be followed. We describe the simple ones that are.
Collapse temperature, and the hour of the cycle where shelf life is lost
The physics of the drying cycle explains why some cakes are matte and full-volume and others are glassy discs, and why the difference is not cosmetic.
What happens in solution that does not happen in the cake
Every degradation pathway accelerates by orders of magnitude on reconstitution, because the solvent that lyophilisation removed is the reagent most of them need.
The reference change value: the number that tells you whether a delta is real
Almost every misreading of a laboratory panel is a misunderstanding of what a reference interval is and how much a result has to move before the movement means anything.
Why the bone question is harder than the muscle question
The evidence base is one secondary analysis, several small studies and a large amount of extrapolation from bariatric surgery.
What a 1 mL syringe does that a 0.3 mL syringe does not
We work through the arithmetic in full, because it is short, and because the errors it prevents are order-of-magnitude errors.
What column temperature does to selectivity
Column chemistry, particle size and pore diameter determine what the separation is capable of before the gradient is even programmed.
A vial can be 99.4 per cent pure and not sterile in the same afternoon
Every certificate circulating in this market answers a question about molecules. Almost none answers a question about organisms, pyrogens, or the integrity of the seal.
Reading the semaglutide composition data without the press release
The composition data comes from imaging substudies enrolling a few score participants at selected sites. It is the best evidence available and it is thin.
The one-quarter rule, and the paper that took it apart
The gap between a defensible recommendation and a confident one is where most of the harm in this subject lives.
What “LC-MS: conforms” tells a reader, which is almost nothing
None of what a checkable identity statement requires is commercially sensitive, and all of it is known to whoever produced the document.
The cold chain in this trade is a gel pack and an optimistic estimate
A gel pack has a finite thermal budget, and once it is spent the payload equilibrates with whatever is outside the box. The only question is how long that takes.
Units, millilitres, milligrams: three scales on one small object
A unit is a volume. A dose is a mass. The bridge between them is concentration, and concentration is a number somebody has to calculate.
Site selection when the tissue has already changed
A rotation scheme that is too complicated will not be followed. We describe the simple ones that are.