Lab tests and reports

How to read your child's blood test report

October 20267 min read

Blood test results often arrive before the appointment, and the page is packed with abbreviations, numbers and columns. This guide explains how the report is laid out: where to find the dates, how the sections are organized, what each complete blood count abbreviation refers to, what the units mean, the range printed next to each value, and flags such as H and L. It does not say whether a value is good or bad: your pediatrician explains that, because they know your child. Every point has its source at the bottom of the page.

This guide explains how a report is laid out, not what the results mean. It contains no reference values and no medical advice. Your pediatrician explains what your child's values mean, reading them together with your child's history and how they are doing. If your child is unwell, call your pediatrician.

At the top of the report you find the details that say whose it is and where it comes from: your child's name and date of birth, the name and address of the laboratory, often the doctor who ordered the test, and an accession or sample number.

There is usually more than one date. The collection date says when the blood was drawn; the report date says when the lab signed off the results. To line up tests over time, the collection date is the one that matters, so that is the one to note down.

Check the name and date of birth straight away: a report with another child's details should be reported to the lab.
If the report has several pages, make sure they are all there: pages often say “page 1 of 3” or similar at the bottom.
At the end there is usually the signature of the doctor in charge of the laboratory, on paper or digital.

Sections and columns

Results are grouped into sections, each with a heading, often in capitals: for example COMPLETE BLOOD COUNT, CHEMISTRY, URINALYSIS. Within each section, every row is one result, that is a single test.

Rows almost always have the same columns, although the order changes from one lab to another:

the name of the test, in full or abbreviated;
the result: usually a number, sometimes a word such as “Negative”, sometimes a number with a symbol in front, such as “<0.5”;
the unit;
the reference range, the two numbers, a low end and a high end, that the lab prints next to the result;
a column for lab flags, such as H, L or an asterisk.

Complete blood count abbreviations, one by one

The complete blood count (CBC), called a full blood count (FBC) in the UK, counts and describes the cells in the blood: red blood cells, white blood cells and platelets. Abbreviations can vary a little between labs. Below is what each number refers to, not whether that number is fine: the definitions come from MedlinePlus and Lab Tests Online.

RBC (red blood cells): how many red blood cells there are, the cells that carry oxygen around the body.
HGB or Hb (hemoglobin): the iron-rich protein inside red blood cells that carries oxygen.
HCT or Hct (hematocrit): how much of the blood is made up of red blood cells.
MCV (mean corpuscular volume): the average size of red blood cells.
MCH (mean corpuscular hemoglobin): the average amount of hemoglobin in each red blood cell.
MCHC (mean corpuscular hemoglobin concentration): how concentrated the hemoglobin is within red blood cells.
RDW (red cell distribution width): how much red blood cells vary in size.
WBC (white blood cells): how many white blood cells there are, the cells that help the body fight infections.
Differential: how the white blood cells split into five types, namely neutrophils, lymphocytes, monocytes, eosinophils and basophils.
PLT (platelets): how many platelets there are, the cells that help blood clot.

In the differential the same name often appears twice. Look at the unit: the row with the % sign says what share of all white blood cells is of that type, the other says how many cells of that type there are in a given volume of blood. They are two ways of writing the same thing, not two different tests.

Units: the same test written in different ways

The unit tells you how to read the number. Some you will often see: g/dL means grams per deciliter; fL stands for femtoliters, the unit used for the volume of a cell; pg stands for picograms; % is a percentage. Cell counts are written in forms such as 10^3/µL or 10^9/L, that is thousands per microliter or billions per liter.

MedlinePlus, the information service of the US National Library of Medicine, points out that different labs may use different units for the same test. So two numbers can only be compared if they have the same unit: 12 g/dL and 120 g/L, for example, say the same thing.

Pediary does not convert units: the trend chart of a result only puts together values with the same unit as the latest test, so it never places side by side numbers that cannot be compared.

The reference range, and why it changes

Next to each value the lab prints two numbers, a low end and a high end: this is the reference range. According to MedlinePlus, it is based on the results of large groups of healthy people. Lab Tests Online notes that your report includes the reference ranges used by the laboratory that ran the test.

The range is not the same everywhere, for three reasons:

The lab. Different methods lead to different ranges, which is why labs may use different ranges for the same test (MedlinePlus).
Age. Children and newborns have different ranges from adults (MedlinePlus, Lab Tests Online).
Sex. For some results, ranges also differ between boys and girls (Lab Tests Online).

In practice, the range to look at is the one printed on your child's report, not a table found online. That is also why this guide contains no numbers.

MedlinePlus adds two useful points: a result outside the range may or may not be a sign of a health problem, and even when every value is within range it is worth talking about the results with your doctor.

H, L, asterisks and arrows

Many labs flag results that fall outside their own range. The most common flags are H, for high, a value above the range, and L, for low, a value below it. Other labs use an asterisk, an up or down arrow, bold type or a color.

A flag says one thing only: that number is outside the range given by the lab. It does not say how much it matters, or whether anything needs to be done. The same number can carry a flag on one report and not on another, if the two labs use different ranges.

Symbols in front of a number, such as “<0.5” or “>100”, mean “less than” and “more than”: the lab does not report the exact value, but says it is below or above that number.

What to ask your pediatrician

The report is one piece of your child's story, not the whole story: your pediatrician reads it together with how your child is doing. To arrive at the appointment prepared, you can bring these questions:

What does this flagged result mean for my child?
Should it be compared with an earlier test? Was that one done at the same lab?
Does anything need to be repeated, and when?
Is there anything I should watch for at home in the meantime?

Bring the whole report, with every page, and earlier reports if you have them, so your pediatrician can compare them if they find it useful.

Keeping reports in order with Pediary

Pediary is a free app for iPhone and Android, with no Pediary account and no ads, that keeps lab tests and medical reports for children and adults, reads the pages of Italian and English reports on the phone, and shows how values change over time.

For a lab test you choose “Scan pages”, “Choose photos”, “Import PDF” or “Enter manually”. The pages are read on the phone: for each result the app suggests the name, value, unit, reference range and lab flag as the lab printed them, plus the collection date. You check every value against the pages before saving; uncertain results arrive switched off and marked “to check”.

Results that carry a lab flag, or fall outside the printed range, are marked “outside the range given by the lab”, with no severity colors. Every result with a number has its own chart over time, with the band of the range given by the lab in the latest test.

Pediary stores your lab tests and medical reports and helps you find them: it does not interpret them or give medical advice. To understand what they mean, talk to your doctor.