Is a vitamin D level of 15 ng/mL acceptable in a patient with a glomerular filtration rate (GFR) of 24 mL/min/1.73m^2, indicating impaired renal function, and should it be treated?

Treatment of Vitamin D Deficiency in a Patient with CKD and GFR of 24

A vitamin D level of 15 ng/mL in a patient with a GFR of 24 mL/min/1.73m² requires treatment with ergocalciferol (vitamin D2) 50,000 IU weekly for 12 weeks, followed by monthly maintenance therapy. 1

Assessment of Vitamin D Status in CKD

The patient's vitamin D level of 15 ng/mL indicates deficiency, which is particularly concerning in the context of advanced chronic kidney disease (CKD stage 4 with GFR 24 mL/min/1.73m²). This level is below the recommended threshold of 30 ng/mL and requires intervention for several reasons:

• Vitamin D levels below 15 ng/mL are associated with greater severity of secondary hyperparathyroidism in CKD patients 1
• CKD patients have higher prevalence of vitamin D deficiency due to:
  • Reduced sun exposure
  • Lower intake of vitamin D-rich foods
  • Reduced endogenous synthesis
  • Increased urinary losses of vitamin D-binding protein in proteinuric states 1

Treatment Protocol

Initial Treatment Phase

• Prescribe ergocalciferol (vitamin D2) 50,000 IU orally once weekly for 12 weeks 1
• This aggressive replacement is appropriate for documented deficiency (level <15 ng/mL) in CKD

Maintenance Phase

• After the 12-week loading period, continue with ergocalciferol 50,000 IU monthly 1
• This maintenance dose helps sustain adequate vitamin D levels in the context of impaired kidney function

Monitoring

• Check serum calcium and phosphorus monthly for the first 3 months of therapy, then every 3 months thereafter 1
• Measure 25(OH)D levels after at least 3 months of supplementation 2
• Monitor PTH levels every 3 months during treatment 1

Rationale for Treatment

1. Prevention of Secondary Hyperparathyroidism: 25(OH)D levels below 15 ng/mL are associated with more severe secondary hyperparathyroidism, even in advanced CKD 1

2. Bone Health Protection: Vitamin D supplementation may help reduce fracture risk and improve bone mineral density in CKD patients 2

3. Potential Renoprotection: Some evidence suggests vitamin D supplementation may help preserve remaining kidney function. A study showed that cholecalciferol supplementation in vitamin D-deficient CKD patients taking ACE inhibitors/ARBs helped prevent decline in GFR 3

4. Altered Vitamin D Metabolism in CKD: Patients with GFR <30 mL/min have impaired conversion of 25(OH)D to active 1,25(OH)₂D, making vitamin D deficiency particularly problematic 4, 5

Important Considerations

• Choice of Vitamin D Form: Ergocalciferol (vitamin D2) is preferred over cholecalciferol (vitamin D3) in CKD patients based on available evidence and commercial preparations 1

• Avoid Active Vitamin D for Nutritional Deficiency: Calcitriol or other 1-hydroxylated vitamin D sterols should not be used to treat nutritional vitamin D deficiency 1

• Safety Monitoring: Treatment should only be initiated if serum calcium is <9.5 mg/dL and phosphorus <4.6 mg/dL 1

• Additive Effects: Vitamin D deficiency and reduced GFR have additive effects on increasing PTH levels, making correction of vitamin D status particularly important in CKD 6

Caution

Do not delay treatment of vitamin D deficiency in this patient. The K/DOQI guidelines specifically note that 25(OH)D levels below 15 ng/mL pose a major risk factor for severe secondary hyperparathyroidism in CKD patients 1. While some guidelines suggest not routinely prescribing vitamin D supplements in the absence of documented deficiency 1, this patient has documented deficiency that warrants treatment.