help with lab interpretation...

I think that the value is within the normal variation for lab results. A little bit of dilution of the blood (too much saline, not enough blood) could cause a slight drop. This is particularly likely if the sample was drawn from an existing IV line that had fluid running through it. It could also be slightly diluted if the patient had just received a bolus of fluid.

When you're first getting into this stuff, the tendency is to think pretty concretely. I think that sometimes nursing school encourages this thinking that every single lab and assessment finding must have a specific and easily identifiable cause. What you'll learn is that labs are just one tool in your toolbox and that you can't really tell much about a patient without completely integrating each part of the patient's picture - symptoms, assessments, meds, labs and other studies.

I admire your persistence, but when you get into comparing a series of normal values, you're unlikely to be able to pinpoint specific causes of these small decreases. Was it an exposure to a viral illness? A response to a random med? A technical issue with the phlebotomy? A quality control issue with the lab technology? Who knows? In the real world, with no mention of any change in the patient's status, this isn't something that we would hone in on.

One minor point is that a differential is the section of the CBC that counts and compares the different types of white cells. The two values that you see for each type of cell would be the absolute and relative values.

Thank you so much for taking the time to answer this! I had a feeling I was thinking about it too much :)