Imagine you want to know how much iron, HGC or cholesterol you have in your blood, what does people look at? I try to search on internet and fail to find. I naively imagined it would be with a microscope but also… it feels weird and would ask to like… count manually?
Just wondering how they do…
In: Biology
It depends on what you’re testing for.
For many tests, you add one or more chemicals to a sample of blood to react with the thing you’re testing for, and then quantitatively measure some result of the reaction.
For example, in the [CDC’s documented procedure for measuring serum iron](https://www.cdc.gov/nchs/data/nhanes/nhanes_01_02/l40fe_b_met_iron_tibc_alpkem.pdf) a chemical called ferrozine is added to a small amount of blood. Ferrozine reacts with the iron in blood to form a compound that is purple. The intensity of the purple color is directly proportional to the amount of iron-ferrozine complex, and so to the amount of iron in the sample. You measure the intensity of color by using a piece of lab equipment called a colorimeter.
For other things, you _can_ literally count them. Take a drop of blood, put it on a microscope slide, and count say the number of white blood cells you see per square millimeter. Count a bunch of square millimeters, average out the count, then scale it up from the volume of one square millimeter of blood in a microscope slide to something standard like a milliliter.
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