Every letter we have printed

Ion suppression is the point I would put in bold. A species that ionises poorly in the presence of an excess of something that ionises well can be present at several per cent and invisible in the spectrum. Absence of a peak is not absence of a compound, and the report cannot tell you which you have.

A small defence of the linear MALDI instrument. It is fast, it tolerates dirty samples, and for a synthesis chemist checking that a chain has grown by the residue intended it is entirely fit for purpose. The problem is not the instrument. It is printing its output on a release document.

A limit expressed in endotoxin units means nothing without a per-kilogram basis and a route, which is where the specification actually lives. Numbers quoted in this market are usually bare figures with no denominator at all.

Endotoxin is not a sterility question and the two are treated as one throughout this market. A preparation can be sterile and carry endotoxin, because the material is a fragment of a cell wall and survives the process that killed the organism.

I photograph every cake now because of an earlier piece of yours, and last month it paid for itself. Two vials from the same box, one a proper matte plug and one a collapsed glassy disc. The supplier replaced both without argument when I sent the photographs.

The badges that do resolve to a third-party page are a genuine improvement and deserve saying so. I have followed several from companies in your dossier programme and reached a report with a number, a date and a lot on it, which is precisely what the mechanism is for.

There is an argument that the badge is aimed at the seller rather than the buyer: it exists so that suppliers who test can distinguish themselves from those who do not. If that is the purpose, it is a poor consumer instrument being asked to do a trade-signalling job.

Credit where it is due: all four answered your questionnaire and answered it on the record. In my experience of trying to get straight answers out of laboratories in other sectors, that is not the normal outcome, and it says something about how these organisations see their role.

Intervals differ between laboratories because the assays differ, and results from two laboratories cannot be compared without the intervals beside them. People compare them constantly and the difference is attributed to their own biology.

Some analytes have intervals that vary with body composition, which makes them awkward to interpret in exactly the population most likely to be measuring them. That interaction is real and is rarely mentioned in general discussion.

My ferritin fell from 118 to 34 across a year on treatment and I was told this was expected because inflammation had fallen. Six months later I was clearly iron deficient. I appreciate the section on this being ambiguous, but the ambiguity was resolved in one direction and nobody looked.

Correction to your HbA1c section. You write that chronic kidney disease lowers HbA1c through shortened erythrocyte survival. It can also raise measured values on some assay platforms through carbamylated haemoglobin interference. The net direction depends on the method.

A small thing but it matters in practice: your table gives amylase and lipase rising as a finding of unclear significance. In my laboratory we no longer report amylase at all for suspected pancreatitis, because lipase is more sensitive and more specific and having both invites the wrong one to be acted on.

Sharps disposal is not an afterthought and the article treats it as one. A rigid container, obtained before it is needed rather than after, is the whole of the advice, and it belongs at the start of the sequence rather than at the end.

The stopper is the critical surface and the one people touch. Once a stopper has been handled, the disinfection performed before handling it is no longer relevant, and the order of operations is the whole technique.

Hydration is the dominant short-term error term in most of these methods and the least controlled. A standardised fasting and fluid protocol before scanning would tighten these datasets more than any statistical technique.

The smallest change an instrument can resolve is the number readers most need and are least often given. Below that threshold a difference between two scans is not a small change; it is not a change at all, and treating it as one drives a great deal of unnecessary anxiety.

Vitamin D and calcium status are collected in some of these protocols and reported in almost none, despite being obvious effect modifiers. Where the data exists, publishing it would cost nothing.

An observation from the receiving end. When we are sent numbered samples with no context we ask more questions of the data, because we cannot lean on an expectation. Blinding improves the analysis as well as the credibility, and that argument is never made.

Publication bias applies here as much as anywhere. A blind programme that publishes only its interesting findings has a denominator problem, and readers have no way to reconstruct the denominator from the outside.

A suggestion for the services rather than for you: publish a price for a full package including the raw data files. I would pay it, my colleagues would pay it, and at present there is no line on any of the four price lists that lets me.

Custody matters most exactly when the result is bad, which is when nobody has a record. The discipline has to be in place before it is needed, and the incentive to establish it only appears afterwards.

I run a small teaching laboratory and I use this department as reading for second-year students. The point that lands hardest with them is that four defensible analytical choices can move a reported figure by nearly two points without anyone behaving badly. They arrive believing measurement is a fact and leave understanding it is a procedure.

Our institution requires two decimal places on a purchase specification and I have never once seen a certificate that could support the second one. The precision of the printed number and the precision of the measurement behind it have drifted apart, and nobody in the chain has an incentive to say so.

You write that only one laboratory attached its chromatogram to the private buyer report. That was probably us. We started doing it five years ago because the PDF seemed incomplete without it. It costs us nothing to add — the instrument generates it automatically — and it solves exactly the dispute-resolution problem you describe. More laboratories should do it, and the reason they do not is not technical.

Weight-bearing changes as mass changes, and the mechanical loading on the skeleton changes with it. Any bone finding in a mass-loss study is confounded by that mechanically, quite apart from anything pharmacological.

Site matters enormously. Spine, hip and forearm measurements diverge in the same individual over the same period, and a single reported figure without the site is close to uninterpretable.

Your piece treats the one-quarter rule as discredited and then quotes fractions of one third and two fifths from the substudies as though those were more solid. They are group means from a hundred and forty people. Physician, heal thyself.

Trials that included a structured activity component and trials that did not are compared directly in most coverage, and the component is one of the largest determinants of the composition outcome. It should be the first thing in any comparison table.

Specifications that are set after the result is known are not specifications, they are descriptions. The tell is a limit that sits a fraction below the reported value on every lot. Where a company publishes one limit and holds it across a catalogue, it is telling you the number was decided in advance.

The word conforms is doing exactly the work you describe. A result of 97.8 against a specification of not less than 95 conforms; so does 99.6. The certificate that prints only the verdict has told me the material passed a test whose difficulty I am not allowed to know.

The published trials that continued longest are the ones least discussed, presumably because their results are the least dramatic. A quiet extension study is more informative about a long commitment than any headline finding from a twelve-month arm.

Reported adherence in the maintenance phase of published trials is high and self-reported adherence outside them is not measured at all. Any comparison between trial outcomes and general experience has that gap in it and rarely acknowledges it.

A reason absent from every list: the person stopped believing the material was what it claimed to be. In a market where that is a live question, it is an obvious category, and no clinical taxonomy would ever include it.

Reporting the number scanned at each timepoint, rather than only at baseline, would let a reader see the attrition directly. It is a single extra row in a table and it is almost never present.

The proportion of loss that is lean tissue is broadly consistent with what is seen in dietary weight loss of similar magnitude, which is the comparison readers need and rarely get. The question is not whether lean mass falls but whether it falls more than it would otherwise.

Hydration state, recent exercise and time of day all move these estimates, and serial scans done under different conditions are not comparable. Standardising the conditions is free and it is the single largest improvement available to anybody tracking themselves.

Mass loss of any origin is associated with density change in the older literature, which makes the untreated comparator essential and frequently absent. Without it the question of attribution cannot be approached at all.

Nothing in this area has been studied in the population that most reads about it, which is people acquiring material outside a clinical setting and training without supervision. Every figure is a read-across and should be labelled as one.

Glycated haemoglobin reflects roughly the preceding two to three months, weighted towards the more recent weeks, which means a value taken four weeks after a change is a poor test of that change. It is the commonest misreading of the analyte and it is entirely avoidable by waiting.