Complete blood count in children and adults

What should you be familiar with when interpreting the CBC?

The range of numbers – this is confusing. The range, i.e the limits for what is normal and abnormal, differs depending on age and gender, and can even be different depending on the lab at which the test is done.
Therefore, not all values that are marked in red and lie outside the exact range present a clear and immediate danger and justify the skip of a heartbeat. I have yet to meet someone completely healthy whose lab results are all within the normal range. If you happen to come across anyone like that, have them see a doctor ASAP.

Additionally, there are certain conditions at which having higher levels of white blood cells will be completely normal to me, whereas others clinical situations at which seeing that will leave me concerned.
It is therefore important to realize – blood count results should always be interpreted within clinical context and by a professional. And there is no need to lose yourself over every little value outside the noted acceptable range.
In addition, as I have already explained, some of the values and ranges vary between different labs. Your neighbor may have a value on his CBC test results that you may not have.
Also, often the units of measurements differ between labs. This difference is usually in thousands such that a value of 5 K/micl in one lab may be presented as 5000 micl in another. Watch out for this.

How is a CBC performed in a child and adult and is fasting necessary before the test is taken?

One can carry out a CBC by taking blood either from a finger prick or a venous sample, usually around the area of the elbow (the front portion), when taking other blood tests.
When interested in taking a CBC only, without any extra blood tests, one can do so by taking a small amount of blood from a finger prick.
If the CBC was taken as part of a larger workup, together with a biochemistry panel and other tests, the child will most probably have to have blood drawn from a vein in the elbow area, and a CBC tube will be sent together with several other tubes for the remainder of the tests.
What about fasting? If it is only CBC we are taking blood for, there is absolutely no need to fast prior to the test.

When should a CBC be performed in a child?

Practically speaking, there are two main indications for taking a complete blood count as an only test.
a. At the age of 1 year – in some countries, this is a very common indication, carried out for assessment of the red cell count (hemoglobin). You can read more about why this test is importent here. Note, it may be possible to spare the child from this test.
b. When a child has fever, in order to evaluate whether the infection is of viral or bacterial origin – practically, the pediatrician or the doctor on call refers the family to this test usually after several days of fever, so as to assess whether the infection is viral or bacterial.
It the infection is bacterial; we expect the white cell counts to rise. If it is viral, not so much. Since this test doesn’t require a venous sample, but only quick and simple finger prick – it was selected as the test of choice for evaluation of fever. Is it accurate? Only very grossly.
Unfortunately, there are cases when children may have significant bacterial infections and their white cell count will not vary, and children with viral infection whose white cell count may confuse us and elevate greatly. In the meantime, it is all we’ve got, until the possibility of checking for other, more accurate, inflammatory markers (did you say CRP or procalcitonin?), at the local clinics and labs is made available, we will have to do with CBCs.
Of course, CBCs are also taken sometimes as one of several tests taken as part of a more complex medical workup for a child.

What are the different blood components seen in CBC test results?

To make things simpler I will discuss each of the three lines assessed separately:

Blood components related to the white blood cell lineage:

White blood cell count / WBC – one of the main reasons we have gathered here for today. The number of white blood cells present in a person’s blood. The values vary depending on age, and as I mentioned previously, higher values could indicate bacterial infection.
A high level of white blood cells is called leukocytosis; a low level, leukopenia.
When interpreting the white blood cell count value, one must always look at the differential. The differential is actually the different types of white blood cells present and their sum is the total number of WBCs. Each type of cell has a different name and most results will present both their absolute number and their percentage.

Percentage of neutrophils / NEUT / Neutrophils % – neutrophils are a type of white blood cell whose job is to fight bacterial infections. The value given is a percentage of all the white cells. When the test is carried out because an infection is suspected, this is one of the more important values to be looking at. Now, if we have the WBC as an absolute value and the neutrophils as a percentage, it is possible to understand the absolute neutrophil count result, as well.
The amount of neutrophils/ ANC / Absolute neutrophil count / NEUT.abs / Neutrophils absolute – no matter the name, this is the absolute count of neutrophils calculated from the neutrophil percentage, out of the total white blood cell count and we could have actually calculated this number on our own in our head, or using a calculator
Why is each value presented twice? Once as a percentage and once as an absolute value? These are two different aspects, that give slightly different information.
A high value of neutrophils is referred to as neutrophilia.
A low value of neutrophils is referred to as neutropenia.
If we get neutrophils, we will be able to get that there are other types of white blood cells, their strange names are as follows:
Lymphocytes / LYM / Lymphocytes% – these are elevated mainly in viral infections.
Monocytes / MONO / Monocytes% – a type of white blood cells that rise during different viral infections (for example, infectious mononucleosis).
Eosinophils / EOS / eosinophils% – we usually see a mild elevation in children with some sort of allergy (atopic dermatitis, asthma, etc.) and often if there is an infection due to a parasite. On the other hand, most of the time when the eosinophils are elevated, the elevation has no clinical significance.
Basophils / BASO / Basophils% – with all due respect to basophils… they are not as important in our constellation.
LUC / Large Unstained Cells% – white cells with a shape that does not belong to any of the previously mentioned cells. A high level can indicate a viral infection or a blood condition.
Note that each of these cells, just like neutrophils, have both an absolute value and are shown as a percentage.

Components related to the red cell count:

The red blood cell lineage takes up the most space in the complete blood cell count, and the job of most of the blood components related to it is to provide different elements to the healthcare professional who is trying to evaluate for any relevant abnormalities.
Hemoglobin / HB / HGB – the most important value related to the red cell count. Normal values differ depending on age and between men and women. A lower value means anemia, of any cause (bleeding, iron-deficiency, vitamin B12 deficiency and more). You can read more about iron-deficiency anemia in infants and children in the link here.
Red blood cells count / RBC – the red blood cell is attached to a molecule called hemoglobin, that is responsible for carrying oxygen. Therefore, the number of red blood cells is another value we need to look at when the hemoglobin level is low. For example, in iron-deficiency cases, both the hemoglobin and the red blood cell count decrease. By contrast, in certain conditions in Thalassemia, the hemoglobin value may be low, but the red blood cell count will be normal.
Hematocrit / HCT – the volume percentage of red blood cells in the blood. This is usually a mirror image of the hemoglobin value, and a low number indicates anemia.
The next few values in the red blood cell lineage provide the physician with extra information about the different segments in the red blood cell lineage. Some of the information provided by these other values may overlap, and so I will focus on the important ones:
Mean cellular volume / MCV – in iron deficiency this value decreases. A good example of when this result is important is when looking at a one-year old’s CBC; a value below 74 could indicate iron deficiency (with or without anemia).
This value is also related to others that are tested for in the CBC:
Micro%, Macro%, Hypo%, Hyper% – all of these are additional values in the red blood cell line that help the physician understand the reason behind the person’s condition, which is usually anemia.
This also applies to other components such as MCH or MCHC, which estimate the amount of hemoglobin in each cell.
RDW / Red Cell Distribution Width – the amount of red blood cell variation in size.
Again, it’s true that each one of these blood components has a certain importance, but there is no need to go into further detail in this chapter.

Components related to platelets:

This is the third lineage that is tested for in the CBC.
Platelet count / PLT – generally speaking, a value between 150 thousand to 450 thousand is considered normal. Values slightly above or below the normal are common in healthy children and also when a person is sick or has fever.
Mean platelet volume / MPV – a test that is significant only when the number of platelets itself is very low. Since the size of younger platelets is larger than that of older platelets, the presence of more young platelets will elevate this value.
A high platelet value is referred to as thrombocytosis.
The medical term for a low platelet value is thrombocytopenia.

So how shall we summarize all of this?
A 25-lines-long results sheet that is under daily use in pediatrics, and in the right hands can serve to aid a physician and family detect important medical conditions. On the other hand, strange values that are slightly outside the normal range are quite common and it is up to the experienced physician to determine which of the abnormalities are significant and which are less important.
At the same time, I hope this chapter helps parents comprehend what each one of the important blood components means and beyond that, which ones are significant and what they should be looking for when reading CBC results.