Renal Osteodystrophy

1. Pathophysiology
   1. Primary: Decreased Glomerular Filtration Rate
      1. Hypocalcemia
         1. Decreased Vitamin D activity and deficiency with decreased calcium absorption
      2. Hyperphosphatemia
         1. Phosphate retention
   2. Secondary Hyperparathyroidism
      1. Contrast with Primary Hyperparathyroidism (where calcium is increased and phosphate low)
      2. Results in increased Osteoclast activity and increased bone turnover
   3. Ultimate bone impacts
      1. Oseteomalacia
      2. Osteitis Fibrosa Cystica
2. Labs
   1. Serum Phosphate
   2. Serum Calcium
   3. Parathyroid Hormone
   4. 25-Hydroxyvitamin D
      1. Also increases PTH
      2. Replace if <30 ng/ml
3. Management: Parathyroid Hormone (PTH) target
   1. Target Parathyroid Hormone
      1. Stage 3: 35-70 pg/ml
      2. Stage 4: 70-110 pg/ml
      3. Stage 5: 150-300 pg/ml
   2. Initial Steps: Measures to suppress PTH Secretion
      1. Treat Hyperphosphatemia
      2. Give Calcitriol
      3. Give Vitamin D Analogs
   3. Persistent rise in PTH despite initial steps
      1. 25-OH-Vitamin D <30 ng/ml
         1. Replace with Ergocalciferol or Cholecalciferol
      2. 25-OH-Vitamin D >30 ng/ml: Give Cacitriol (if calcium <9.5, phosphorus <5.5, CaxPO4 <55)
         1. PTH 70-300 (ckd3) or 110-300 (ckd4) Calcitriol 0.25 mcg/day
         2. PTH 300-600: Calcitriol 0.5 to 1.0 mcg/day
         3. PTH 600-1000: Calcitriol 1 to 2 mcg/day
   4. Persistent rise despite above in Dialysis patients
      1. Calcimimetic: Cinacalcet (Sensipar)
         1. Suppresses PTH by increasing Parathyroid Gland's calcium-sensing receptor sensitivity
4. Management: Phosphate
   1. Serum Phosphorus Target
      1. Stage 3-4 CKD: 2.7 to 4.6 mg/dl
      2. Stage 5 CKD: 3.5 to 5.5 mg/dl
   2. Dietary phosphate restriction
      1. Limit phosphate to 800-1000 mg/day
      2. Indication
         1. PTH increased
         2. Phosphate levels >4.6 mg/dl
   3. Phosphate binders
      1. Calcium Carbonate (Tums)
      2. Sevelamer (Renagel)
      3. Calcium Acetate (PhosLo)
   4. Avoid
      1. Calcium Citrate (citracal)
      2. Aluminum based binding agents (due to aluminum deposition in bone)
5. Management: Calcium
   1. Serum Calcium and Serum Phosphate Target
      1. Keep Ca x PO4 <55
   2. Keep total calcium 8.4 to 9.5
      1. Maximum Dietary Calcium 2000 mg/day (including calcium based binders)
   3. Total Serum Calcium <8.4 (or PTH>55)
      1. Oral Calcium supplement
      2. Oral Vitamin D
      3. Calcitrol (Rocaltrol) 25 mcg every other day
   4. Total Serum Calcium >9.5 or PTH below goal
      1. Discontinue Calcium Supplementation
      2. Avoid calcium-based phosphate binders
      3. Avoid Vitamin D
6. Complications
   1. Osteitis Fibrosa Cystica