Phosphorus Disorders

NORMAL RANGE FOR PHOSPHOROUS:

2.5 - 4.5 mg/dL

Absoprtion of Phosphorous

occurs in…the gut

• Increased BY:

  • ACTIVE vitamin D (1,25 dihydroxyvitamin D3) 

  • PTH

  • Low phosphorus diet 

• Decreased BY:

  • HIGH dietary intake of phosphorus and magnesium 

  • Glucocorticoids 

  • Hypothyroidism 

FG23: Fibroblast Growth Factor 23

→ regulates PHOSPHORUS homeostasis 

• Decreases tubular reabsorption in kidney (increasing phosphaturia)

• Inhibits 1-a-hydroxylase (enzyme needed for vitamin D activation)

Hyperphosphatemia 

• Serum phosphorus > 4.5 mg/dL

Causes: 

• Renal impairment 

• Iatrogenic 

• Rapid tissue breakdown 

• Acid-base imbalance (acidosis) 

Calcium-P soft tissue deposition

• Acute: intrarenal calcification, nephrolithiasis, obstruction 

• Chronic: eye, skin, heart, vessel, lung, GI deposition

can lead to hypocalcemia

Hyperphosphatemia Treatment…

1. Phosphate binders 

   1. Bind phosphorus in the gut (chronic treatment/PREVENTION

2. Calcium 

   1. Treats emergent hyperphospatemia leading to hypocalcemia 

Hypophosphatemia 

1. Low serum phosphorus 

   1. Mild = phosphorus 1-2 mg/dL

   2. Severe = phosphorus < 1 mg/dL 

      1. Life threatening 

      2. Metabolic encephalopathy (weakness, parethesia, numbness, seizure, coma

      3. Rhabdomylosis 

ETIOLOGIES…of hypophosphatemia 

1. GI (reduced absorption) 

   1. Alcoholism 

   2. Medications (cations)

2. Kidney (reducde re-absorption) 

3. Re-distribution (shifts to intracellular)

Hypophosphatemia Treatment…

1. V phosphate replacement for severe/symptomatic 

   1. Beware of hypomagnesemia with IV phosphorous use

2. PO phosphate replacement for mild/moderate asymptomatic 

RECAP:

→ phosphate binders used to treat non-emergent hyperphosphatemia 

→ hyperphosphatemia can lead to Ca-P precipitation