A third-party laboratory report can look authoritative at a glance: a logo, a table of numbers, a chromatogram, a signature. But the value of a report depends on details that are easy to skim past. To read third-party lab results accurately, you need to know where those details sit. This guide walks through a typical analytical report section by section and explains what each part can, and cannot, tell you.
For background on the analytical methods themselves, see our Testing & Documentation Guide. This article focuses on the practical skill of reading the document in front of you.
Start With the Basics: Who, What, and When
Before looking at any result, confirm that the report identifies the parties and the sample clearly. A report that cannot answer these questions gives you little to work with, no matter how good the numbers look.
The issuing laboratory
The report should name the laboratory that performed the analysis, with a physical address and contact details. A logo alone is not enough. You should be able to find the same laboratory independently, through its own website or an accreditation directory, rather than relying only on the contact details printed on the report.
The client
Many reports list the client who submitted the sample. This matters because it tells you who commissioned the work. A report requested by the vendor selling the product is still vendor-supplied documentation, even if a separate laboratory performed the analysis. “Third-party” describes who ran the test; it does not tell you who chose the sample.
The sample description
Look for a sample name, a laboratory sample or report number, and ideally a batch or lot number supplied by the client. The more specific the description, the easier it is to connect the report to a particular product. A report describing only a compound name, with no lot number, cannot be tied to any specific production batch.
The dates
Most reports list a date received, a date analyzed, and a date reported. Check that these are in a logical order and that the report is reasonably recent relative to the product being offered. An older report may still be accurate for the sample tested, but it says nothing about material produced later.
Reading the Results Table
The results table is where most readers go first. Read each row as an answer to a specific question, and check that the question is the one you care about.
Test, method, result, and units
A well-constructed row names the test (for example, “Purity” or “Identity”), the method used (such as HPLC-UV or LC-MS), the result, and the units. Missing units are a problem. “99.1” means nothing until you know whether it is a percentage of total peak area, a percentage by weight, or something else.
Specification or acceptance criteria
Some reports include a specification column, such as “≥98.0%,” and a pass/fail statement. Note who set the specification. Laboratories generally report results against criteria the client provides, so a “pass” means the sample met the client’s chosen threshold, not an independent quality standard.
Purity, identity, and quantity are different questions
These three terms are often blurred together in marketing, but they answer different questions:
- Purity usually refers to how much of the detected material corresponds to the main component. For peptides it is commonly reported as HPLC peak-area percentage, which is relative to what the detector sees, not an absolute weight measurement.
- Identity asks whether the main component is the compound it is claimed to be. This is typically supported by mass spectrometry, comparing an observed mass with the theoretical mass of the expected sequence.
- Quantity or content asks how much of the compound is actually present, for example milligrams per vial. A sample can show high HPLC purity and correct identity while containing less peptide than the label states, because lyophilized peptide powders also contain counter-ions (such as trifluoroacetate or acetate salts) and residual water.
If a report gives only a purity figure, it has not addressed identity or quantity. Our article on understanding HPLC for peptides explains why peak-area purity has these limits.
Mass spectrometry results
An identity result usually lists an expected (theoretical) mass and an observed mass. Peptides often appear as multiply charged ions, so a spectrum may show peaks at a fraction of the full molecular mass, such as [M+2H]2+ or [M+3H]3+. A competent report explains which ion it is reporting. Also check whether the report uses monoisotopic or average mass, since these differ for larger molecules and comparing one with the other can create an apparent mismatch.
Basic mass spectrometry supports identity but does not confirm the full amino acid sequence. Tandem methods (LC-MS/MS) that fragment the peptide can provide sequence-level evidence. A report should not be read as confirming more than the method performed.
“ND,” “<LOQ,” and other qualifiers
Results for contaminants are often reported as “ND” (not detected) or “<LOQ” (below the limit of quantitation). These do not mean “zero.” They mean the substance was not detected or not measurable above the method’s limits. A meaningful report states what those limits are. Without them, “ND” is hard to interpret.
Endotoxin and sterility results
If present, endotoxin results are usually reported in endotoxin units (EU) per milligram or per vial, measured with a Limulus amebocyte lysate (LAL) or recombinant method. Sterility testing is a separate test with its own procedure. A purity or identity result says nothing about either. The FDA’s guidance Pyrogen and Endotoxins Testing: Questions and Answers provides background on how endotoxin testing is framed in regulated settings.
Reading the Supporting Data
Raw or semi-raw data, such as a chromatogram or mass spectrum, is more informative than a summary number alone.
- Chromatogram: Look for axis labels, a retention time for the main peak, and a peak table. A chromatogram with no axes or peak table is difficult to evaluate.
- Peak table: Check that the main peak’s area percentage matches the purity reported in the results table.
- Mass spectrum: Look for labeled peaks and a clear indication of which peak corresponds to the expected compound.
Mismatches between the summary table and the supporting data are worth noting. They may reflect a simple transcription error, but they reduce confidence in the document.
Signatures, Accreditation, and Disclaimers
Most reports end with an authorization block: an analyst or reviewer name, a signature, and sometimes an accreditation statement or symbol. If a laboratory claims ISO/IEC 17025 accreditation, that accreditation covers specific methods listed on its scope, not everything the laboratory does. Accreditation is discussed in more detail in why certificate of analysis verification matters.
Read the fine print. Many reports state that results relate only to the sample as received. That sentence is accurate and important: the report describes one sample, not a batch, a product line, or a vendor.
A Quick Reading Checklist
- Is the laboratory named and independently findable?
- Who was the client, and who selected the sample?
- Is there a report number and a batch or lot number?
- Are the dates logical and reasonably current?
- Does each result include a method and units?
- Does the report address purity, identity, and quantity, or only one of them?
- Do supporting chromatograms and spectra match the summary?
- Are detection limits stated for “ND” results?
- Can the report be confirmed with the issuing laboratory?
Key Takeaways
- A report describes the sample that was tested; it does not automatically describe a batch, a product line, or a vendor.
- “Third-party” tells you who ran the analysis, not who commissioned it or chose the sample.
- Purity, identity, and quantity are separate questions that need separate evidence.
- Units, methods, detection limits, and supporting data are what make a result interpretable.
- Specifications on a report are often set by the client, so “pass” is relative to that choice.
Disclaimer: This article is educational and explains how to read laboratory documentation. It does not evaluate any specific product, and it is not medical, legal, or purchasing advice.