Accepted answer
12 weeks is 84 days, and the first question about any marker is whether 84 days is long enough for it to have finished moving. Serum magnesium represents about one per cent of body magnesium, which is why it can sit mid-range while intake has been inadequate for months. Against 84 days that puts the marker well inside its own settling time, so the value is reporting a new steady state rather than a transient. 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 84 days in, with no baseline drawn under the same conditions, is a number rather than a change — and nothing here is medical advice.
Start with a baseline. A result taken before anything started converts most later ambiguity into a simple comparison, and it cannot be obtained retrospectively.
Same laboratory, same method, same time of day, same fasting state. Between-laboratory differences on several common analytes are larger than the changes people are trying to detect.
Keep the reports rather than the numbers. Units, reference intervals and methods all vary, and a bare number two years later is not comparable to anything.
Biological variation data are published per analyte and are the basis for the reference change value — the difference between two results that is larger than noise.
Ordering tests you will not act on generates anxiety and incidental findings, both of which have costs.
Decide the action for each result before you order the test.
Minor: haemolysis inflates potassium enough to cause a fright over what is a handling artefact. – bea_castellanos 8 months ago Adding a vote because this deserves more of them. – dmitri_savchuk 6 months ago add a comment