CKD and Calcium Metabolism: Key Points for GP's

Chronic kidney disease (CKD) profoundly disturbs the delicate balance of calcium (Ca), phosphate (PO₄), vitamin D, and parathyroid hormone (PTH). As GFR declines, the kidneys fail to excrete phosphate and to activate vitamin D, leading to:

Abnormality	Mechanism	Consequence	Typical Stage
↓ Vitamin D Activation	↓ 1α-hydroxylase → ↓ calcitriol (1,25-dihydroxyvitamin D) → ↓ intestinal Ca absorption	↓ Serum Ca (hypocalcemia)	Begins CKD stage 3 (eGFR <60)
↑ Phosphate Retention	↓ Renal excretion → ↑ serum phosphate	Binds Ca → ↓ serum Ca Promotes vascular calcification	Early CKD (eGFR <60)
Secondary Hyperparathyroidism	Low Ca + ↓ calcitriol chronically stimulate parathyroid glands	↑ PTH → ↑ bone resorption → renal osteodystrophy	Typically CKD stage 3–5
↑ FGF-23	Early rise to ↑ phosphate excretion	Suppresses 1α-hydroxylase → further ↓ calcitriol → worsens hypocalcemia	Early CKD (stages 2–3)
Reduced Receptor Sensitivity	CKD milieu (↑ phosphate, uraemia) ↓ Ca-sensing and vitamin D receptor expression in parathyroid glands	↓ Feedback sensitivity → further ↑ PTH	Advanced CKD
Bone–Mineral Axis Dysregulation	Disruption of kidney–parathyroid–bone signalling	CKD-MBD: high-turnover bone disease (osteitis fibrosa) or low-turnover (adynamic bone disease)	CKD stages 3–5

Chronic kidney disease (CKD) sets up a “perfect storm” for mineral imbalance:

↑ Phosphate retention and...

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