HYPERPHOSPHATEMIA
Hyperphosphatemia = Serum phosphate > 4.5 mg/dL (1.45 mmol/L) in adults
|
Severity |
Serum Phosphate |
|
Mild |
4.6–6 mg/dL |
|
Moderate |
6–9 mg/dL |
|
Severe |
>9–10 mg/dL |
Life-threatening when associated with:
- Hypocalcemia
- Arrhythmias
- Acute kidney injury
- Tumor lysis syndrome
Normal Phosphate Physiology
Distribution
- 85% – bone (hydroxyapatite)
- 14% – intracellular
- <1% – extracellular (measured serum phosphate)
Normal Serum Level
- Adults: 2.5–4.5 mg/dL
Serum phosphate exhibits a marked circadian rhythm, with a peak around 3:00 am and a nadir around 11:00 am. As hemodialysis removes phosphate, the timing between sampling and the last dialysis session is also important.
Regulation of Phosphate Homeostasis
|
Hormone |
Effect on Phosphate |
|
PTH |
↓ Renal reabsorption → ↓ phosphate,↑ Calcium |
|
FGF-23(Produced by osteocytes) |
↓ Renal reabsorption , ↓ Vit D |
|
1,25Vitamin D |
↑Intestinal absorption(jejunum) |
|
Kidneys |
Excrete ~90% of daily load |
📌 Phosphate is primarily regulated by the KIDNEY
ETIOLOGY
Major Mechanisms
- Decreased renal excretion (MOST COMMON)
- Increased phosphate load
- Shift from intracellular → extracellular
- Hormonal dysregulation
1. Decreased Renal Excretion (Commonest Cause)
Chronic Kidney Disease (CKD)
- If GFR <30 mL/min → phosphate retention
- Leads to:
- Secondary hyperparathyroidism
- Renal osteodystrophy
- Vascular calcification
Acute Kidney Injury
- Especially:
- Tumor lysis
- Rhabdomyolysis
- Hemolysis
|
Condition |
Mechanism |
|
Hypoparathyroidism |
↓ phosphate excretion |
|
Pseudohypoparathyroidism |
PTH resistance |
|
Acromegaly |
↑ renal phosphate reabsorption |
|
Vitamin D excess |
↑ intestinal absorption |
2. Increased Phosphate Load
Exogenous
- Phosphate-containing laxatives/enemas
- IV phosphate
- Total parenteral nutrition (TPN)
- High phosphate diet
- Vitamin D intoxication
⚠️ Sodium phosphate enemas → fatal hyperphosphatemia in elderly/CKD
Endogenous
- Tumor lysis syndrome
- Rhabdomyolysis
- Massive hemolysis
- Severe burns
- DKA treatment
- Status epilepticus
- Heat stroke
3. Transcellular Shift
|
Condition |
Mechanism |
|
Metabolic acidosis |
Phosphate shifts out of cells |
|
Diabetic ketoacidosis (DKA) |
Insulin deficiency |
|
Lactic acidosis |
Cell breakdown |
|
Hypercatabolic states |
↑ cell lysis |
4. Laboratory Artifact (Pseudohyperphosphatemia)
- Hyperlipidemia
- Hyperproteinemia
- Paraproteinemia
- Hemolysis
- Hyperbilirubinemia
- Liposomal amphotericin B
Clinical Manifestations
⚠️ Hyperphosphatemia itself is generally asymptomatic,Symptoms often due to HYPOCALCEMIA
Neuromuscular
- Perioral numbness
- Paresthesia
- Muscle cramps
- Tetany
- Seizures
- laryngospasm
Cardiac
- QT prolongation
- Arrhythmias
- Hypotension
Skeletal / Soft Tissue(Chronic symptoms)
- Bone pain
- Fractures
- Vascular calcification
- Calciphylaxis (precipitation of calcium phosphate in tissues)
- Corneal calcification
- Renal osteodystrophy
Dermatologic
- Pruritus (uremic)
- Skin necrosis (calciphylaxis)
COMPLICATIONS
1. Hypocalcemia
- Ca × PO₄ product ↑ → calcium precipitation
- Suppresses neuromuscular transmission
2. Secondary Hyperparathyroidism
- CKD-related mineral bone disease (CKD-MBD)
3. Metastatic Calcification
- Vessels
- Heart valves
- Lungs
- Skin
📌 Ca × PO₄ product > 70 mg²/dL² → high risk of Calciphylaxis
DIAGNOSIS
|
Test |
Purpose |
|
Serum phosphate |
Confirm diagnosis |
|
Serum calcium |
Look for hypocalcemia |
|
Creatinine, urea |
Renal function |
|
PTH |
CKD vs endocrine |
|
Vitamin D |
Excess/deficiency |
|
ABG |
Acidosis |
|
CK, LDH, uric acid |
TLS / rhabdomyolysis |
Special Scenarios
- TLS → ↑ phosphate, ↑ uric acid, ↓ calcium
- DKA → phosphate may fall after insulin
- CKD → ↑ PTH, ↓ calcitriol
MANAGEMENT
Treat the underlying cause
- AKI → optimize perfusion, treat obstruction, manage renal failure.
- Tumor lysis → aggressive hydration (if appropriate), uric acid-lowering therapy, dialysis if indicated.
- Rhabdomyolysis → fluids, treat hyperkalemia, monitor CK and renal function.
- Hypoparathyroidism → manage with calcium and active vitamin D while monitoring phosphate.
Stop Phosphate Intake
- Discontinue phosphate-containing drugs
- Low phosphate diet
Typically 800–1000 mg/day in CKD with persistent hyperphosphatemia.
Avoid:
- Cola beverages
- Processed foods with phosphate additives
- Organ meats
- Processed cheese
- Packaged meats
Phosphate Binders (Oral)
|
Drug |
Dose (with meals) |
Notes |
|
Calcium carbonate |
1–3 g/day (≈ 500–1500 mg elemental Ca/day) in divided doses |
Cheap, widely available. Avoid in hypercalcemia, adynamic bone disease, vascular calcification. |
|
Calcium acetate |
1334 mg TDS |
Preferred Ca-binder if calcium used.Avoid in hypercalcemia,vitamin D intoxication, Ca-Phos product > 66 |
|
Sevelamer carbonate |
800–1600 mg TDS |
First-line in CKD G4–G5D with hypercalcemia. ↓ LDL, ↓ CRP. No metabolic acidosis. |
|
Sevelamer HCl |
800–1600 mg TDS |
Can cause hyperchloremic metabolic acidosis. |
|
Lanthanum carbonate |
500 mg TDS (chewable) |
Effective, low pill burden. Tablets must be chewed. |
|
Ferric citrate |
2 tablets TDS |
↓ PO₄ + iron absorption → ↓ IV iron & ESA dose. Monitor ferritin, TSAT. |
|
Sucroferric oxyhydroxide |
500 mg TDS |
Minimal systemic iron absorption. Low pill burden. Dark stools common. |
Symptomatic Cases
1. Treat Hypocalcemia
⚠️ DO NOT give calcium unless symptomatic
- Risk of metastatic calcification
- Indications:
- Tetany
- Seizures
- Arrhythmias
2. Volume resuscitation, followed by forced diuresis using acetazolamide +/- loop diuretic.
3. Dialysis (DEFINITIVE)
Indications
- Severe hyperphosphatemia
- AKI/ESRD
- TLS
- Symptomatic hypocalcemia
- Volume overload
📌 Hemodialysis > Peritoneal dialysis