Phosphorus
Everything you need to know about Phosphorus levels, including what normal ranges look like and what abnormal results might indicate.
Standard Reference Range
Unit: mg/dLReference ranges may vary slightly between laboratories. Always consult your doctor for interpretation.
What is Phosphorus?
Phosphorus (measured as phosphate) is essential for bone health, energy production (ATP), and cell membranes. It works closely with calcium in bone metabolism.
Key Takeaway
Phosphorus and calcium have an inverse relationship. Abnormal levels often indicate kidney disease or parathyroid disorders.
Why is this test performed?
Phosphorus testing helps:
- Evaluate kidney function
- Assess parathyroid disorders
- Investigate bone diseases
- Monitor vitamin D therapy
- Evaluate acid-base balance
Interpreting Your Results
Low Phosphorus (Hypophosphatemia)
＜2.5 mg/dL indicates low phosphorus:
Mild (2.0-2.5):
- Usually no symptoms
Moderate (1.0-2.0):
- Muscle weakness
- Bone pain
- Fatigue
Severe (＜1.0):
- Respiratory failure
- Heart failure
- Confusion, seizures
- Hemolytic anemia
Common Causes:
- Refeeding syndrome
- Vitamin D deficiency
- Hyperparathyroidism
- Diabetic ketoacidosis (recovery phase)
- Malabsorption
- Phosphate binders
- Chronic alcoholism
High Phosphorus (Hyperphosphatemia)
＞4.5 mg/dL indicates high phosphorus:
Symptoms:
- Itching (chronic)
- Bone and joint pain
- Calcification of soft tissues
- Usually asymptomatic unless very high
Common Causes:
- Kidney disease (most common)
- Hypoparathyroidism
- Vitamin D toxicity
- Tumor lysis syndrome
- Rhabdomyolysis
- Excessive phosphate intake
Clinical Significance
Calcium-Phosphorus Product: Ca × P product should be ＜55-60
- Higher values increase risk of tissue calcification
- Important in chronic kidney disease management
Inverse Relationship with Calcium:
- PTH ↑ → Phosphorus ↓, Calcium ↑
- PTH ↓ → Phosphorus ↑, Calcium ↓
Treatment
For Hypophosphatemia:
- Oral phosphate supplements
- Treat underlying cause
- IV phosphate (severe cases)
- Increase dietary phosphorus
Phosphorus-Rich Foods:
- Dairy products
- Meat and poultry
- Fish
- Nuts and seeds
- Whole grains
For Hyperphosphatemia:
- Low-phosphorus diet
- Phosphate binders (with meals)
- Dialysis (if kidney failure)
- Treat underlying cause
Important in Chronic Kidney Disease
As kidney function declines:
- Phosphorus retention occurs
- Leads to secondary hyperparathyroidism
- Causes bone disease (renal osteodystrophy)
- Management crucial to prevent complications
Related Tests
- Calcium: Inverse relationship
- PTH: Regulates both Ca and P
- Vitamin D: Increases phosphorus absorption
- ALP: Marker of bone turnover
- Creatinine: Assess kidney function
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