Blood tests: how to read a complete blood count (CBC), line by line

So you got your blood test results - and there are values in red and you've spiraled into a stress loop. Don't worry, I'm here to explain every line in a routine panel, what it means, when you can simply relax, and what to watch for. We'll do this in several parts, and today, in part one, we'll talk about the complete blood count (CBC) - one of the most common tests you'll have.

I'm Dr. Elisheva, I'm an anesthesiologist, and here you'll get clear, direct medical information - no scare tactics and no drama - so you can make informed decisions about your health. Let's get started.

## Important rules for understanding blood tests

Before we begin, it's important to know a few rules.

The first rule is that you don't look only at what's red - everything has to be interpreted in a clinical context, meaning you connect it to how you feel - the complaints and symptoms you have - and take into account the reason you did the tests in the first place.

Second rule - a value that's just a touch outside the range is rarely meaningful.

Third rule - when there's an abnormal result that doesn't fit the clinical picture, very often the first thing we do is simply repeat the test to confirm it's a real result and not some lab error - because that happens more than you'd think.

And of course, a reminder that this video is for general guidance only, and for any uncertainty, symptom, or significant deviation - consult your treating physician.

## What is a complete blood count (CBC)?

A CBC is a test of the cells in the blood - and we have 3 groups of cell types:

- red blood cells, whose job is to bring oxygen to the tissues, - white blood cells, which have a role in the immune system, - and platelets, which have a role in the clotting system.

Why is a CBC ordered? It's a super-routine test that's sent every time blood work is done - it could be before surgery, in cases of fatigue or weakness, recurrent infections, prolonged fever, or suspected infection.

So let's look together at each line of the CBC and decode it - I'll also say that the lines I skip are ones that are not meaningful or are a value that repeats itself.

## Red blood cells (carry oxygen to the organs)

Let's start with the red blood cells.

The first number is the RBC, red blood cells - the total count of red blood cells. Because the main component of red blood cells is hemoglobin - the protein that binds oxygen - we usually actually look at it more than at the RBC.

If hemoglobin is too low - that's below 12 for a woman and below 13 for a man - that's a condition called anemia. The classic symptoms of anemia are fatigue, weakness, and pallor. There are many, many possible causes of anemia, and the treatment for a large share of them is effective and fairly simple - like iron-deficiency anemia or folic-acid deficiency.

To figure out the source of the anemia there are a few more indices we look at - mainly two values that appear in every count:

- MCV - the size of our cells, - MCH - the concentration of hemoglobin per cell.

For example, in iron-deficiency anemia the MCV and MCH are low. In anemia from B12 deficiency, folic-acid deficiency, or sometimes due to alcoholism - both of these indices will be high. Anemia with normal MCV and MCH can appear in other situations, such as chronic diseases, or simply a combined anemia from several causes at once.

The next step in such a case is often to order blood iron and iron-store tests, vitamins, and folic acid - to clarify the source.

Hemoglobin that's too high, above the normal range - that's a condition called polycythemia. It can be caused by smoking, chronic respiratory diseases, sometimes dehydration, certain hematological diseases, or by living at high altitude - if you're lucky enough to live at a ski resort, for example, your number may be above normal. Sometimes, if the number is truly significantly high, there are symptoms of headaches, dizziness, and itching after a hot shower.

Another index we have is hematocrit - it's a measure of how concentrated our cells are within the blood fluid. It generally tracks with the hemoglobin - so if hemoglobin is low, it will be low, and especially if it's high it can be a sign of dehydration.

## White blood cells (the immune system)

Let's move on to the white blood cells.

First we have the white blood cells, WBC - the total count of white blood cells.

If the number is too high - the most common reason is a state of acute infection or inflammation - for example, if you do the test while you have the flu, it will be high, because the immune system is dealing with an illness. So usually, in such a case, it will come along with signs of some illness. When it's too low - it's very context-dependent; it can also paradoxically be low around an illness, or be a sign of immune deficiency or some problem in the production of these cells.

When the number is high or low, we're interested in seeing the breakdown of the white blood cell types, because that points us to the cause of the deviation from normal. But before we get into that, you need to understand something critical - notice that all these cells are written twice: once as an absolute number, that is, a quantity, and once as a percentage of the total cells. What matters here is the absolute number of cells, not the percentage.

In most labs there are consistent, recurring deviations that cause the percentages to be flagged outside the normal range - and that's meaningless.

So now we can look at these subtypes:

- when neutrophils are high - that points to a bacterial-source infection. - when lymphocytes are high - that points more to a viral-source infection, that is, a virus. Often, especially in children who have had a fever for a few days, this is used to decide whether or not to give antibiotics. - high eosinophils - often in cases of allergy.

The next step, with abnormal white blood cells, if there's no story of a recent illness that explains it - is to repeat the test, and then maybe send additional, more in-depth tests to clarify the cause - depending of course on how significant the deviation from normal is.

## Platelets (the clotting system)

And let's move on to the last group - platelets.

As we said, platelets have a role in the clotting system. First we have the platelets - the platelet count.

If they're too low - it can be from all sorts of causes: autoimmune diseases, sometimes as a result of certain medications, infections, and in rare cases malignant diseases that prevent their normal production. And the symptoms we sometimes see in cases of low platelets are increased bleeding, for example recurrent nosebleeds.

If the number is too high - it can be around an acute illness, since they act as a kind of inflammation marker, and there are also hematological diseases that do this. It's also something seen in iron-deficiency anemia - it can come together with high platelets. Usually there are no symptoms in such cases, but sometimes it can go along with headaches, dizziness, and tingling in the fingers.

In addition, we have a value called MPV - the size of the platelets. In certain cases, when the platelet count is abnormal, we look at it to point us toward the cause - but it doesn't have much value on its own.

That's it. I hope this video helped you. In the next part we'll talk about the blood chemistry panel, so subscribe to the channel so you don't miss it. You can leave me questions below and I'll answer. See you in the next video.