Accepted answer
2 weeks is 14 days, and the first question about any marker is whether 14 days is long enough for it to have finished moving. Creatinine is produced from muscle at a rate proportional to how much of it there is, so a falling creatinine during weight loss is a body-composition result before it is a renal one. Against 14 days the marker is at or near the edge of its own settling time, so part of what you are reading is the transition rather than the destination. The second question is the denominator. Weight loss moves plasma volume, muscle mass and intake at once, and several of the markers on a routine panel are ratios with one of those three underneath them. Repeat before interpreting. A single value 14 days in, with no baseline drawn under the same conditions, is a number rather than a change — and nothing here is medical advice.
Standardise the conditions — same time of day, same fasting state, same laboratory — or you are measuring the conditions rather than yourself.
Delta checks — comparing against your own previous value — are far more sensitive than comparing against a population interval, which is the argument for keeping a series rather than a snapshot.
A twenty-analyte panel run on a healthy person will produce, on average, one out-of-range result purely from how reference intervals are constructed. That is arithmetic rather than pathology.
External quality assurance schemes document between-laboratory differences on common analytes that routinely exceed the size of clinically interesting changes.
Decide the action for each result before you order the test.