Is ferritin worth drawing at baseline before starting liraglutide?

Setup, so nobody has to ask: ferritin · liraglutide.

The failure mode I am trying to avoid is making this decision emotionally.

I have twelve months in view and I would like the plan to survive that long.

How would you structure this, and what thresholds would you set in advance?

The relevant statistical point is that a ninety-five per cent reference interval means one analyte in twenty will read out of range in a healthy person by construction.

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.

To be exact about it, 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.

Baseline first, then a repeat under identical conditions. Everything else is secondary.

Before reacting to any single value, check whether it is outside the interval by an amount larger than the assay's own variation.

Timing matters per analyte: cortisol and testosterone are diurnal, triglycerides are postprandial, and creatinine responds to hydration and to recent training. Fixing the conditions removes most of the noise.

It helps to be literal here: a sensible core for this population is a full blood count, renal function with electrolytes, liver enzymes with bilirubin, a fasting lipid panel with apolipoprotein B, HbA1c and thyroid-stimulating hormone.

Keep the full report, not the number. You will need the units and the interval later.

The short version: a small, well-chosen panel with a baseline beats a large one without.

Haemolysis in the sample raises potassium and several enzymes spuriously. If a result is bizarre, ask whether the sample was flagged before building a theory on it.

Ordering tests you will not act on generates anxiety and incidental findings, both of which have costs.

Same laboratory, same time, same fasting state, or the comparison is not a comparison.

The honest position is that most people order too many analytes and too few time points, when the reverse would be more informative.

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.

Reference intervals are conventionally the central ninety-five per cent of a reference population, which is the direct cause of the one-in-twenty out-of-range rate on a healthy panel.

Decide the action for each result before you order the test.