Analytics · Home & field testing · continued

Coming back to: Lateral-flow and colorimetric approaches: the specificity problem posts 61–90

Analytics › Home & field testing third-party testing LOD & LOQ documentation quality ELISA Solved

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.

h.iyerTL229 Jun 2026#61

BDraganov, post #22: I had written a reply contradicting post #18 and deleted it. Here is what survived. False positives and false negatives: no test has 100% sensitivity and 100% specificity. A negative result does not guarantee absence; a positive result does not guarantee presence. The predictive value depends on prevalence. Go to post

A request rather than an answer: could whoever has the primary source for Lateral-flow and colorimetric approaches post it? I have seen the claim three times this month and each version had lost a qualifier.

16 likes in reply to #22 29d

blank_injectionTL2Analytical chemist30 Jun 2026#62

The right question for any home test is: what physical quantity does it measure, and what would have to be true for that quantity to answer your question? Most disappointment comes from skipping it.

Written in the hope of being told what I have missed.

31 likes 28d

n.villalobosTL21 Jul 2026#63

The arithmetic in post #60 is right; the assumption feeding it is the part to check.

Colorimetric and lateral-flow methods generally respond to a class of chemistry rather than to a specific molecule. They can often distinguish something from nothing and rarely distinguish one peptide from a close relative.

0 likes 27d

forest_plotTL3Evidence synthesis2 Jul 2026#64

Answering the question post #62 raises rather than the one it answers.

The tare problem is the catch with weighing: vial-to-vial glass mass varies, so the useful measurement is the spread across a consignment rather than an absolute figure.

3 likes 26d

s.antonsenTL23 Jul 2026#65

n.ramos, post #16: Colorimetric and lateral-flow methods generally respond to a class of chemistry rather than to a specific molecule. They can often distinguish something from nothing and rarely distinguish one peptide from a close relative. A weak preference rather than a position. Go to post

Confirming post #64 from a second method, which matters more than confirming it from a second person.

Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.

22 likes in reply to #16 25d

q.zhao_qaTL3Quality assurance4 Jul 2026#66

e.kimani, post #31: Colorimetric tests: colour intensity correlates with concentration, but the relationship is non-linear at extremes and the correlation depends on the exact conditions (pH, temperature, timing). Reading the colour visually introduces subjectivity. Go to post

False positives and false negatives: no test has 100% sensitivity and 100% specificity. A negative result does not guarantee absence; a positive result does not guarantee presence. The predictive value depends on prevalence.

That matches what I was told, which is not the same as knowing it.

0 likes in reply to #31 24d

i.lehtinenTL25 Jul 2026 · edited#67

Source for the Lateral-flow and colorimetric approaches figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.

Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.

1 like 23d

unit_conversionTL3Regular6 Jul 2026#68

Post #66 describes the usual case. This is about the unusual one.

I disagree with the framing of Lateral-flow and colorimetric approaches above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.

The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.

6 likes 22d

z.cardosoTL27 Jul 2026#69

Taking post #68 at face value and following it one step further.

6 likes 21d

electrolyte_notesTL2Regular8 Jul 2026#70

Post #66 and I disagree about the size of the effect, not about the direction.

I would put moderate confidence on the mainstream reading of Lateral-flow and colorimetric approaches and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.

17 likes 20d

a.kravchenkoTL29 Jul 2026#71

Adding a small correction to the Lateral-flow and colorimetric approaches summary above rather than a disagreement with it. The substance holds; one of the figures is out by a factor that matters.

9 likes in reply to #16 19d

BirkelandTL310 Jul 2026#72

Collapsed as off-topic by two members at trust level 3 or above

Ultraviolet absorbance at 280 nanometres estimates concentration for peptides containing aromatic residues and gives nothing for peptides that do not. Knowing which yours is comes first.

That is one dataset and I would not build a rule on it.

v.rautioTL211 Jul 2026#73

Reading back through, this was answered upthread and I missed it. My fault.

0 likes 17d

b.jankowiakTL3Regular12 Jul 2026#74

f.laurent, post #41: Lateral-flow and colorimetric approaches looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour. Go to post

The tare problem is the catch with weighing: vial-to-vial glass mass varies, so the useful measurement is the spread across a consignment rather than an absolute figure.

The mechanism is plausible, which is not the same as established.

29 likes in reply to #41 16d

ar.kravchenkoTL213 Jul 2026#75

s.demir, post #9: Post #7 is right about the mechanism and I think understates the practical bit. Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively. Happy to expand any of that if it is the useful part. Go to post

Colorimetric tests: colour intensity correlates with concentration, but the relationship is non-linear at extremes and the correlation depends on the exact conditions (pH, temperature, timing). Reading the colour visually introduces subjectivity.

I am not the right person to answer the follow-up to this.

14 likes in reply to #9 15d

s.grahameTL2Member14 Jul 2026#76

Whatever the answer on Lateral-flow and colorimetric approaches turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.

5 likes 14d

e.roosTL215 Jul 2026 · edited#77

On post #74 — agreed on the reasoning, with one qualification.

I have been on both sides of the Lateral-flow and colorimetric approaches argument in this category within eighteen months, which should tell you how strong the evidence for either side is.

0 likes 13d

citation_indexTL2Member16 Jul 2026#78

Picking up post #77: that is the part I would want checked first.

A home refractometer is not measuring what people hope it is measuring in these preparations, and the readings are dominated by everything other than the peptide.

0 likes 12d

n.zielinskiTL217 Jul 2026#79

Collapsed as off-topic by two members at trust level 3 or above

Where I part company with post #77, and it is a narrow parting.

Photographs of test results posted here are worth including with the lighting and the timing stated, because both change the apparent result of a colorimetric method substantially.

endpoint_marginTL2Member18 Jul 2026#80

n.villalobos, post #63: The arithmetic in post #60 is right; the assumption feeding it is the part to check. Colorimetric and lateral-flow methods generally respond to a class of chemistry rather than to a specific molecule. They can often distinguish something from nothing and rarely distinguish one peptide from a close relative. Go to post

Post #77 is the version of this I will quote in future. One addition.

Lateral-flow devices: like a rapid COVID test. They have a reagent strip and produce a colour result. They are quick but not precise and not intended for quantitative work.

The reasoning is more useful than the number, which is why I have shown it.

0 likes in reply to #63 10d

p.iyer_pharmdTL3Pharmacist19 Jul 2026#81

This follows post #78 rather than contradicting it.

Reading a colorimetric result at the wrong time is the commonest procedural error. Development is time-dependent and the window is usually narrow.

20 likes 9d

h.iyerTL220 Jul 2026#82

My position on Lateral-flow and colorimetric approaches is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly.

0 likes 8d

hana.satoTL4 Moderator21 Jul 2026#83

Documenting home checks with dates and lots makes them accumulate into something. Undocumented ones evaporate and get remembered selectively.

Filing this under things that are true until someone shows me otherwise.

2 likes 7d

n.okwuosaTL222 Jul 2026#84

j.palacios, post #21: Colorimetric tests: colour intensity correlates with concentration, but the relationship is non-linear at extremes and the correlation depends on the exact conditions (pH, temperature, timing). Reading the colour visually introduces subjectivity. Go to post

What physical quantity does the device measure? A colorimetric or lateral-flow method typically responds to a class of chemistry rather than to a specific molecule. It can distinguish "peptide present" from "nothing present" but generally cannot distinguish the intended peptide from a closely related one.

It took me longer than it should have to see that.

8 likes in reply to #21 6d

forest_plotTL3Evidence synthesis23 Jul 2026#85

b.aalto, post #49: Photographs of test results posted here are worth including with the lighting and the timing stated, because both change the apparent result of a colorimetric method substantially. It is worth stating the boring hypothesis before the interesting one. Go to post

Understood, and I withdraw the assumption I opened with.

14 likes in reply to #49 5d

e.steinerTL224 Jul 2026#86

Written quickly, so the reasoning may be tighter than the wording.

28 likes 4d

blank_injectionTL2Analytical chemist25 Jul 2026#87

Something worth flagging about Lateral-flow and colorimetric approaches: the strongest-sounding claims in this thread are the ones with no source attached, which is the usual pattern and not a coincidence.

0 likes 3d

n.villalobosTL226 Jul 2026#88

Everything in post #84 holds. The case it does not cover is the one I have.

Reframing Lateral-flow and colorimetric approaches slightly, because I think the disagreement is about the question rather than the answer. If the question is "does it happen", yes. If it is "how often", nobody here knows.

5 likes 2d

v.bhattacharyaTL227 Jul 2026#89

h.iyer, post #61: A request rather than an answer: could whoever has the primary source for Lateral-flow and colorimetric approaches post it? I have seen the claim three times this month and each version had lost a qualifier. Go to post

Ultraviolet absorbance at 280 nanometres estimates concentration for peptides containing aromatic residues and gives nothing for peptides that do not. Knowing which yours is comes first.

Flagging that the sources on this are thinner than the confidence in the thread suggests.

0 likes in reply to #61 1d

s.rasmussenTL228 Jul 2026#90

Counterpoint on Lateral-flow and colorimetric approaches, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has ruled the dull one out.

0 likes 9h

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Coming back to: Lateral-flow and colorimetric approaches: the specificity problem posts 61–90

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