Revisiting: Can a home kit substitute for a laboratory report? A careful no

Revisiting: Can a home kit substitute for a laboratory report? A careful no — setting out what I have, and where I think it stops being reliable.

Working through the identity arithmetic and I would like it checked.

retatrutide has a monoisotopic mass close to 4731.3 Da. On an electrospray instrument I would expect to see the multiply charged series rather than the intact singly charged ion, so for the doubly charged species I calculate (4731.3 + 2 x 1.00728) / 2, and for the triply charged the analogous expression.

The observed values in the report sit within a few ppm of those. My question is what that actually establishes, because I have seen people treat a mass match as a purity result and I do not think it is one.

This follows the opening post rather than contradicting it.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

What you can use home tests for: confirmation that a solution contains peptide (as opposed to being saline alone), rough screening for very different compounds (semaglutide versus totally unrelated compound). What you cannot use them for: precise purity assessment or verification that the identity is correct.

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.

Coming back to post #3, because the follow-up matters more than the original answer.

Why third-party testing is stronger: a home test run by the person who made the compound is a self-selected result. The test run by a neutral third party removes obvious sources of bias.

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.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

Immunoassay limitations: tests that use antibodies have cross-reactivity limitations. An antibody raised to semaglutide will cross-react to some degree with tirzepatide and other structurally similar compounds. The test result conflates them.

Sample handling matters: if a sample is contaminated or degraded before testing, the test gives you the result for the degraded sample, not for fresh material. That is not a failure of the test; it is the test working correctly.

Enzyme assays: if you have an enzyme that reacts specifically with your compound, an enzyme-based assay can work. These are sometimes available commercially but are less common than antibody-based tests.

This follows post #8 rather than contradicting it.

Precision of home tests: most consumer-accessible devices are not precise to the level people want ("is this 99% pure or 97% pure"). They give a yes/no or a rough category, not a quantitative number.

I read post #10 twice before replying, because I had assumed the opposite.

Molecular tests: DNA or RNA tests are not applicable to peptides, which do not contain nucleic acids. Peptide-specific tests rely on protein recognition, not nucleic-acid detection.

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.

Sample handling matters: if a sample is contaminated or degraded before testing, the test gives you the result for the degraded sample, not for fresh material. That is not a failure of the test; it is the test working correctly.