My recent blood tests showed slightly low kidney function what does this mean?

Maybe nothing: BUN and creatinine are meaningful only in the context of your overall health and body type. A very muscular man who eats a lot of meat will have both of these quite elevated and get called a kidney case. If you're older, if you're taking an NSAID, or if you actually have mild kidney disease (hypertension and diabetes are the most common), you'll need to seek the cause with your Dr.

Low: I am assuming you mean that your Creatinine is increased and the GFR is lower? Depending on the amount of reduction of your GFR, there needs to be followup and test done to determine what is the reason. Please remember I am assuming your question here. Urine test is key, and labs may be repeated and cause determined when possible and followed.