A lab report is a dense page, and almost none of it is designed for the person the blood came from. It is a record passed between a laboratory and a clinician. Once you know what each block is for, the page stops being a wall of numbers.
The header: who, when, and from what
The top of the report identifies the sample rather than the result. Expect a patient name and age, a sample or accession number, the name of the requesting doctor, and two dates that are easy to confuse: when the sample was collected, and when it was reported. A report run on Tuesday for blood drawn on Monday carries both.
There is usually a specimen line too — serum, plasma, whole blood, urine. It matters because the same marker measured in a different specimen is a different measurement.
The result block
This is the table everyone looks at, and it has four columns doing four different jobs.
The test name is whatever that laboratory calls it, not a universal name. "SGPT", "ALT" and "Alanine Transaminase" can all appear for the same enzyme, and two labs will print two of them.
The result is the measured value. The unit beside it is part of the result, not decoration: the same substance is reported in different units in different countries, and a number without its unit means nothing.
The reference interval is the range that laboratory considers usual. MedlinePlus describes it as "a set of numbers that form the high and low ends of the range of results that's considered to be normal", built "based on the test results from large groups of healthy people". It belongs to the lab that printed it.
Flags
Many reports mark results that fall outside the interval, commonly with an H, an L, an
asterisk, or bold type. A flag is arithmetic: it says the number sits outside the range printed
next to it on that page. It is not a diagnosis and not a severity rating.
MedlinePlus is explicit that a result outside the range "may or may not be a sign of a health problem. It's common for healthy people to sometimes have results outside the reference range" — and that "a test result that is within a reference range isn't always a guarantee of good health."
The footnotes
The small print at the bottom is where the method lives: which analyser was used, whether a value was calculated rather than measured, whether the sample was haemolysed or lipaemic, and occasionally a note that a result was repeated. When two reports disagree, the footnotes are usually where the explanation is.
What the report does not contain
It does not contain an interpretation. The reference interval tells you what that lab observed in its reference group; it does not tell you what your number means for you, and the NHS notes that a clinician "should talk to you about your results and explain what happens next."
That is the conversation the page exists to support — the report is the evidence, not the answer.