How is phosphate removal managed in patients undergoing dialysis?

Phosphate Removal Management in Dialysis Patients

Phosphate removal in dialysis patients requires a stepwise approach starting with dietary restriction to 800-1,000 mg/day, followed by phosphate binders when serum phosphorus exceeds 5.5 mg/dL, with the target range being 3.5-5.5 mg/dL for Stage 5 CKD patients. 1

Target Serum Phosphorus Levels

• Maintain serum phosphorus between 3.5-5.5 mg/dL (1.13-1.78 mmol/L) in dialysis patients (CKD Stage 5) 1, 2
• Levels above 5.5 mg/dL are associated with increased mortality and cardiovascular complications 1
• Monitor serum phosphorus monthly following initiation of dietary restriction 1

Stepwise Management Algorithm

Step 1: Dietary Phosphorus Restriction

• Restrict dietary phosphorus to 800-1,000 mg/day, adjusted for dietary protein needs 1
• This restriction is challenging because a neutral phosphorus balance is difficult to achieve when protein intake exceeds 50 g/day, even with phosphate binders 3
• Be aware that processed foods contain hidden phosphate additives that are readily absorbed 4, 5
• Approximately 30% of dialysis patients take medications containing phosphate salts, contributing a median of 111 mg/day to phosphorus burden 6

Step 2: Initiate Phosphate Binders

Start phosphate binders when serum phosphorus remains >5.5 mg/dL despite dietary restriction 1, 2

Choice of Phosphate Binder:

Calcium-based binders (calcium acetate or calcium carbonate):

• Effective as first-line therapy in most patients 1
• Limit total elemental calcium from binders to ≤1,500 mg/day 1
• Ensure total calcium intake (dietary + binders) does not exceed 2,000 mg/day 1, 2
• Calcium acetate and calcium carbonate both reduce serum phosphorus by approximately 2 mg/dL 7, 8

Non-calcium-containing binders (sevelamer, lanthanum):

• Preferred in patients with hypercalcemia (corrected serum calcium >10.2 mg/dL) 1, 2
• Preferred when PTH levels are <150 pg/mL on two consecutive measurements 1, 2
• Preferred in patients with severe vascular or soft tissue calcifications 1, 2
• Sevelamer reduces serum phosphorus by approximately 2 mg/dL with average doses of 4.9-6.5 g/day 7
• Lanthanum carbonate is initiated at 1,500 mg/day and titrated every 2-3 weeks, with most patients requiring 1,500-3,000 mg/day 9

Step 3: Combination Therapy

If serum phosphorus remains >5.5 mg/dL despite monotherapy with either calcium-based or non-calcium binders, combine both types 1, 2

• This approach allows phosphorus control while limiting calcium load 1
• Continue to monitor total calcium intake to stay below 2,000 mg/day 1, 2

Step 4: Short-Term Aluminum-Based Binders (Rescue Therapy)

For severe hyperphosphatemia (serum phosphorus >7.0 mg/dL), aluminum-based binders may be used for a maximum of 4 weeks as a single course only 1

• Must be replaced thereafter by other phosphate binders 1
• Monitor for aluminum toxicity 1

Step 5: Dialysis Prescription Modification

Consider increasing dialysis frequency or duration when phosphate binders are insufficient or not tolerated 1

• Increasing dialysis duration has a much greater impact on phosphate removal than increasing frequency alone 1
• Long hemodialysis (8 hours, 3 times weekly) reduces serum phosphorus by approximately 0.45 mmol/L and allows approximately one-third of patients to discontinue phosphate binders 1
• Long-frequent hemodialysis (nocturnal dialysis 5-6 times weekly) reduces serum phosphorus by 0.36-0.5 mmol/L and often eliminates the need for phosphate binders entirely 1
• Some patients on intensive nocturnal dialysis require phosphate supplementation in the dialysate to prevent hypophosphatemia 1

Critical Pitfalls to Avoid

Excessive dietary protein restriction: Restricting protein to achieve phosphorus control increases the risk of protein-energy wasting and malnutrition, which is associated with increased mortality 3, 5

Calcium overload: Total elemental calcium intake exceeding 2,000 mg/day increases the risk of vascular calcification 1, 2

Using calcium-based binders inappropriately: Avoid in hypercalcemic patients or those with PTH <150 pg/mL, as this worsens adynamic bone disease and vascular calcification 1, 2

Ignoring phosphate in medications: Central nervous system and cardiovascular medications frequently contain phosphate salts that contribute significantly to daily phosphate burden 6

Prolonged aluminum use: Never use aluminum-based binders for more than 4 weeks due to risk of aluminum toxicity 1

Monitoring Parameters

• Serum phosphorus: Target 3.5-5.5 mg/dL 1, 2
• Serum calcium: Maintain in normal range, preferably toward lower end (8.4-9.5 mg/dL) 2
• Calcium-phosphorus product: Keep <55 mg²/dL² 2
• Intact PTH levels: Monitor to guide calcium-based binder use 1, 2