skip to main content

FGF23 Early Rise CKD Physiology — ESENeph MCQ

Instant feedback + full explanation. One question, done properly.

ModerateChronic Kidney DiseaseFGF23 Early Rise CKD PhysiologyESENeph

A 55-year-old man has CKD G4 with a serum phosphate of 1.9 mmol/L. His FGF23 level is markedly elevated but PTH is only mildly elevated. What does this pattern represent physiologically?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — FGF23 rises early in CKD (before PTH) as a compensatory phosphaturic hormone; it also suppresses 1,25-dihydroxyvitamin D production, eventually contributing to secondary hyperparathyroidism

FGF23 (produced by osteocytes) is the earliest hormone to rise in CKD as a compensatory mechanism to maintain phosphate balance by promoting renal phosphate excretion. It rises before PTH and before serum phosphate becomes elevated. FGF23 also suppresses renal 1-alpha-hydroxylase, reducing 1,25-dihydroxyvitamin D production. This contributes to reduced calcium absorption and eventually stimulates PTH secretion (secondary hyperparathyroidism). Very high FGF23 levels are independently associated with cardiovascular mortality and left ventricular hypertrophy in CKD.

Reference: KDIGO 2017 – CKD-MBD; Isakova et al 2011 – FGF23 in CKD