HYPERPHOSPHATEMIA

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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

  1. Decreased renal excretion (MOST COMMON)
  2. Increased phosphate load
  3. Shift from intracellular → extracellular
  4. 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

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