Does this patient have Vitamin D deficiency?

Vitamin D deficiency (low levels of 25-hydroxyvitamin D) is common in patients with chronic kidney disease, including patients on dialysis. Etiology is likely multifactorial but may be related to diminished capacity of vitamin D production by skin, limited exposure to sunlight, reduced intake of foods rich in vitamin D, and older age. Recent evidence suggests that 25-hydroxyvitamin D may have important roles due to the ability of extrarenal tissues to convert 25-hydroxyvitamin D into the active form, or 1,25-dihydroxyvitamin D. However, the existing evidence is from observational and animal studies. Although repletion of vitamin D deficiency in ESRD appears to be safe in short-term studies, the benefits of repletion on hard clinical outcomes remain undetermined. Therefore, it is uncertain if levels should be measured in the clinical setting and how to manage deficiency if detected.

Key elements in the history

• Usually detected when levels are checked

• The number of 25-hydroxyvitamin D tests being performed has risen

Key symptoms

• Usually asymptomatic, though severe deficiency may be associated with muscle weakness, bone pain, fractures

• In the dialysis population, low concentration of 25-hydroxyvitamin D may also contribute to erythropoetin resistance

Key signs and physical findings

• Usually accompanies other abnormalities in the CKD-MBD syndrome, especially secondary hyperparathyroidism

• Controversies in the differential diagnosis

  • Definitions for deficiency and sufficiency continue to be debated

  • Most commonly accepted thresholds are listed below

    • ▪ Deficiency: 25-hydroxyvitamin D levels less than 10 ng/ml

    • ▪ Insufficiency: 25-hydroxyvitamin D levels less than 30 ng/ml

    • ▪ Sufficiency: level of 30 ng/ml and above is considered to be normal

What tests to perform?

Lab testing

Which tests should I order?

• 25-hydroxyvitamin D level

• Many available tests, with accuracy varying by laboratory/test

How do I interpret test results?

• Deficiency, insufficiency and sufficiency as defined above

How often should I order tests?

• If sufficient, levels can be rechecked again ...

• If deficient or insufficient and treatment is instituted then levels could be checked again following repletion ...

What are the next steps?

• Consider 25-hydroxivitamin D levels along with other mineral metabolism laboratory values

Overall Interpretation of test results (diagnosis, prognosis)

• Recognize that results may vary by assay method and laboratory used

• If possible, use the same laboratory/assay over time

• Consider seasonal variation

• Consider 25-hydroxivitamin D levels along with other mineral metabolism lab values

Controversies in diagnostic testing

• Definitions for deficiency and sufficiency continue to be debated

• given paucity of evidence regarding outcomes following repletion in dialysis patients, it is not clear that levels should be measured in the clinical setting and how to manage deficiency if detected

How should patients with Vitamin D deficiency be managed?

Key treatment concepts

What to do first: REPLETION

• the following regimens have been shown to be successful as repletion schedules:

  1. Ergocalciferol 50,000 IU weekly for 24 weeks

  2. Ergocalciferol 50,000 IU monthly for 6 months

  3. Oral Cholecalciferol 100,000 IU monthly for 15 months

What to do next: MAINTENANCE:

• at least 800 IU daily, more may be needed in colder climates and during winter season

Specific circumstances

• if a patient is found to be vitamin D deficient and is already receiving active Vitamin D analogs, repletion with above regimen in addition to active vitamin D analogs, if undertaken, is likely safe but calcium and phosphorus levels should be monitored monthly

Controversies in patient management

• Given paucity of data on patient level outcomes following repletion, it remains uncertain whether 25D levels should be checked in dialysis patients and if so how this should be managed

• Those that recommend repletion are extrapolating from data in normal populations and few small studies in dialysis patients

What happens to patients with Vitamin D deficiency?

Natural history

• Adequate levels depend on sufficient exposure to ultraviolet light and dietary sources

• Dialysis patients are particularly at risk given limited exposure to sunlight, reduced intake of foods rich in vitamin D

• Depleted stores may lead to insufficient substrate for conversion to the biologically active form

Epidemiology

• In a cohort study of US incident dialysis patients, 78% were deficient (levels between <30 ng/ml) and 18% were severely deficient (levels <10 ng/ml)

• Black race, female sex, winter season, and hypoalbuminemia were the strongest predictors of vitamin D deficiency

Anatomic and/or pathologic consequences

• Fractures

• Systemic consequences, as described below

Physiologic and/or pathophysiologic implications

• Classic effects

  1. Decreased levels of calcidiol in conjunction with decreased activity of 1-alpha-hydroxylase will lead to diminished production of the calcitriol

  2. Decreased calcitriol levels will result in impaired gastrointestinal calcium absorption, negative calcium balance, secondary hyperparathyroidism, and bone disease

• Other systemic effects

  1. Increased infections

  2. Anemia, erythropoetin resistance

  3. Increased mortality

Pharmacologic considerations

• Preparations

  • Plant derived - ergocalciferol - vitamin D2

  • Animal derived - cholecalciferol - vitamin D3

  • While cholecalciferol appears to be more effective in raising levels (possibly due to greater affinity to vitamin D binding protein and hence longer half-life), ergocalciferol remains the most commonly used form in practice.

• Dose and duration of treatment

  • Several dosing regimens appear to be effective in raising 25-hydroxyvitamin D levels (with some studies also showing increased in 1,25-dihydroxyvitamin D levels and decreases in PTH levels) though data on patient level outcomes following treatment are missing

  • The following regimens have been shown to be successful in raising 25-hydroxyvitamin D levels:

    1. Ergocalciferol 50,000 IU weekly for 24 weeks

    2. Ergocalciferol 50,000 IU monthly for 6 months

    3. Oral Cholecalciferol 100,000 IU monthly for 15 months

How to utilize team care?

• Nurses may help track levels and repletion schedules.

Are there clinical practice guidelines to inform decision making?

Applications

• Kidney Disease Outcomes Quality Initiative (KDOQI)

  • No recommendations regarding treatment due to insufficient evidence at the time

• Kidney Disease: Improving Global Outcomes(KDIGO)

  • although randomized controlled trial (RCT) data are lacking, guidelines recommend managing deficiency in a manner similar to what is being done for the general population

Limitations

• KDOQI published in 2003, prior to some of the recent emerging observational and experimental data