How to read it
Plot the patient’s PTH against a simultaneous albumin-corrected or ionized calcium. The key move is recognising that a PTH inside the reference range is inappropriate when calcium is high (points to parathyroid-dependent disease) or low (points to hypoparathyroidism).
Before you place the point
- Same-draw calcium, albumin, phosphate, magnesium, creatinine/eGFR
- 25-OH vitamin D
- Medications: thiazides, lithium, loop diuretics, antiresorptives, biotin (assay interference)