Why Test Results Vary Between Labs: Multi-Lab COA Comparison

Six Labs Tested the Same Retatrutide Kit. The Results Were Close, Weird, and Very Educational.

We recently tested a kit of Uncle Wang Retatrutide 10mg from Nexaph across several independent labs, including Analytical Formulations Inc. (AFI), Freedom Diagnostics, Janoshik, TrustPointe Analytics, Vanguard Laboratory, and the original vendor-provided Janoshik report.

The short version: the labs mostly agreed on the big picture. The material tested as retatrutide, and the purity results were consistently high. The more interesting part was the mass, or net content, where the numbers moved around more than casual COA readers might expect.

That does not mean one lab is the chosen prophet and everyone else is huffing solvent fumes in a broom closet. It means analytical chemistry is a method-driven process. Different labs use different equipment, different sample prep, different calibration assumptions, different software integration, different analysts, and sometimes different vials from the same kit.

Welcome to the part of peptide testing where the science is real, the numbers are useful, and the internet still tries to turn every decimal point into a cage match.

The Big Picture: Purity Agreed, Mass Argued

The most important thing to understand is that purity and mass are not the same measurement.

Purity asks how clean the main peptide peak looks compared to other detectable peaks under that lab's method.

Mass or net content asks how much retatrutide is actually in the vial.

A vial can be very pure and still contain different measured amounts of peptide. A 99.9% purity result does not automatically mean the vial contains exactly 10.00mg. It means the detected peptide peak is very clean relative to the detected impurity peaks.

In this round of testing, the purity numbers were all in the same neighborhood, roughly 99.7% to 99.9% depending on the lab and report. The content results showed more spread, ranging from about 10.18mg to 12.80mg per vial.

That spread is the article. That is the lesson. That is where Randy the Research Rat puts on his little lab coat and tells everyone to stop treating one COA like it came down from Mount Sinai.

Result Summary

Nexaph Is Also Known for Overfills

One important piece of context: Nexaph has become known in this space for overfilled kits. So seeing numbers above the stated 10mg label claim is not automatically surprising.

The vendor Janoshik report showed three bottles at 11.14mg, 11.46mg, and 11.03mg. The third-party Janoshik report came back at 11.49mg. Those results line up pretty well with the idea that this kit was not underfilled, and may have been intentionally or routinely overfilled.

But this is where people need to be careful. "Nexaph overfills" does not mean every lab must report the same overfill number. It means the general direction makes sense. The exact measured content still depends on the lab, the method, the sample, and how the assay is performed.

Why the Numbers Can Vary

1. Different Labs Are Not Running the Exact Same Test

People love to say "it was tested by HPLC" as if HPLC is a magic slot machine where you insert a vial and receive Universal Truth.

That is not how this works.

HPLC is a platform. The final result depends on the column, mobile phase, gradient, detector wavelength, injection volume, sample concentration, calibration curve, integration settings, standards, and analyst decisions. Two labs can both use HPLC and still run meaningfully different methods.

In this group, the labs listed different approaches. AFI used a UV/Vis Beer-Lambert quantitative assay. Freedom Diagnostics listed HPLC with UV detection coupled with mass spectrometry. Vanguard listed HPLC-UV/VIS. TrustPointe used its TM-1004 assay and purity methods. Janoshik reported peptide content and purity through their HPLC-MS workflow.

Those are not identical analytical pipelines. They are different scientific keyholes pointed at the same peptide.

2. Mass Testing Is More Method-Sensitive Than Purity Testing

Purity is usually a relative measurement. It looks at how much of the detected chromatogram belongs to the main peptide peak compared with other detectable peaks.

Mass or net content is a quantitative measurement. It tries to estimate how many milligrams of peptide are in the vial.

That second question is harder. It depends heavily on calibration, reference standards, sample prep, dilution accuracy, and how the lab defines or reports peptide content.

That is why the purity results can all look very similar while the mass results spread out more. The purity results are sitting at the same lunch table. The mass results are in the group chat arguing.

3. Different Vials From the Same Kit May Not Be Identical

The original vendor Janoshik test reported three bottles from the same batch at 11.14mg, 11.46mg, and 11.03mg. That alone shows that even inside one batch, individual vials are not perfect clones.

Lyophilized peptide filling is not a Star Trek replicator. A batch can be consistent enough to be useful while still having vial-to-vial variation.

So when different labs test different bottles, the comparison includes two layers of variation:

Actual vial-to-vial fill variation
Lab-to-lab method variation

Both matter.

4. Some Labs Were Internally Consistent, Even When They Disagreed With Each Other

This is one of the most useful findings.

TrustPointe reported 12.296mg and 12.328mg, which are very close to each other. Vanguard reported 10.18mg and 10.30mg, also close to each other. AFI reported 10.71mg and 10.85mg, again close to each other.

That suggests each lab may have been reasonably repeatable inside its own method. The bigger disagreement appears when comparing one lab's method against another lab's method.

That is an important distinction. Repeatability inside one lab is not the same thing as perfect agreement across all labs.

5. Calibration and Reference Standards Matter

For quantitative peptide testing, the lab needs a way to convert instrument response into a concentration or mass estimate. That usually involves calibration, a reference standard, response factors, extinction coefficients, or other method-specific assumptions.

If one lab's calibration curve or standard behaves differently from another lab's, the final content number can shift. Not because someone is necessarily wrong, but because the assay is built differently.

This is the part people miss when they treat COAs like sports scores. A lab result is not just the machine talking. It is the machine, the method, the standard, the software, and the human running the process.

6. Sample Prep Can Move the Number

Before the sample ever reaches the instrument, someone has to prepare it.

That may involve dissolving the lyophilized cake, rinsing the vial, transferring liquid, choosing solvent, making dilutions, mixing thoroughly, preventing peptide loss to glass or plastic, and making sure the entire sample is represented.

Small differences can matter. A slight pipetting difference, incomplete dissolution, peptide sticking to a surface, or a dilution error can shift the final calculated content.

This is why the analyst matters. The lab tech is not just pressing the Big Science Button while the machine prints out peptide commandments.

7. "10mg" Is Not Always a Simple Scale Weight

With peptides, "mg per vial" is often a calculated analytical result, not simply someone weighing dry powder on a scale.

Depending on the lab and method, the reported number may be affected by how the assay treats water content, salt form, counterions, residual solvents, net peptide content, and the reference standard used for comparison.

This is especially relevant in the research peptide market, where label claims are often treated as simple numbers, but the underlying chemistry is not always simple.

Why Purity Does Not Tell the Whole Story

A high purity number does not automatically tell you the exact amount of active peptide in the vial.

HPLC purity generally tells you how dominant the main peptide peak is under the method used. It does not necessarily account for every form of mass in the vial, including water, salts, counterions, or other material that may not show up the same way under that method.

So when a report says 99.9% purity, that usually means the detectable peptide-related profile looks very clean. It does not mean the entire physical vial is 99.9% active retatrutide by dry weight.

Purity is about cleanliness. Mass is about quantity. Identity is about whether the compound is what it claims to be. They are related, but they are not interchangeable.