Manual Complete Blood count : THE TEST – the method only
Before i get deeper in the method i should tell you about the content of the CBC report …. You can see in the next images about what you can find in CBC report and the reference range of each item (the reference range is taken from Manual of basic techniques for a health laboratory – World Health Organization, Geneva, 2003) and the reference range of the differential WBCs count is from District Laboratory Practice in Tropical Countries – Monica Cheesbroug h – part 2
1) The principle:
As you can see from the previous images containing CBC report items, that CBC test is actually a group of tests…. Of Course, the principle of manual method of CBC test is to perform the test of each item and each item test has its own principle.
2) How to perform the test:
As we said in the principle, you should do the test for items …. But not all items can be tested and also you can test some and calculate the others from the equations we will see soon
The items that can be tested:
- RBCs count
- Hematocrit (HCT) (also called Packed cell volume (PCV))
- Platelet count
- WBCs count
- Differential white blood cell count count
The items that can’t be tested
Of course, there are some items that we don’t mention it here but it is already rare to be found in CBC reports so, we mention the most recommended items
You can click on any item name to see the manual test for this item.
So, in the items that can be tested, Should you determine all of them by testing?
In my opinion, yes ….. but someone can say to me
“you are wrong because we can use the rule of three of normal hematology to calculate Hb from HCT or HCT from Hb and then we can calculate from them the RBCs no.”
Yes, this right, i know the rule of three of normal hematology which is used to check if complete blood count results are valid….. the rule of three is in the next table.
|Rule one||Hgb × 3 = Hct ±2|
|Rule two||RBC × 3.3 = Hgb ±1.5|
|Rule three||RBC × 9 = Hct ±3|
Although you can use this rule but for accuracy it is better to make the test for each item.
But if you prefer to use this rule, my advice to you will be 2 points:
- You should at least perform hematocrit test and RBCs count and calculate hemoglbin and don’t try to calculate RBCs no. because the RBCs no. may be high and microcytic and these rules apply to normal RBCs
- Don’t perform Hb and RBCs count and calculate hematocrit because the errors in hematocrit test is lower than that of Hb test where in Hb test you may face the errors from your photometer and errors in the volumes you used to test but hematocrit test depends on centrifugation which has minor errors.
So, form this discussion, we can conclude the following:
- There are some tests that should be tested and can’t be calculates from any equations:
- There are some tests that is recommended to test them but can be calculated from the rule of three:
Continue to page 2 to know how to conclude the equations of the items that should be calculated