Vitamin D Therapy in Clinical Practice: One Dose Does Not Fit All

P. J. Ryan


Int J Clin Pract. 2007;61(11):1894-1899. 

In This Article


Patients attending a district general hospital metabolic bone clinic were routinely assessed over 6 years with measurements of their 25 OH vitamin D at first clinic visit or within 4 weeks of their clinic appointment. New patients had records made of their serum 25 hydroxy vitamin D, corrected serum calcium, and whether or not they were taking calcium and or vitamin D supplements. Patients not on supplements and who were not hypercalcaemic and who did not have renal calculi, but with a low baseline vitamin D (below 50 nmol/l) were treated with supplements and then had a repeat measurement after at least 3 months to assess whether or not they were replete. The majority of patients were given Calcichew D3 Forte two tablets per day but over the 6 years of the study a variety of different preparations were used.

Vitamin D samples were sent from Medway Hospital to Kings College Hospital for analysis. At Kings College Hospital, vitamin D was measured by the IDS gamma-B-OH Vitamin D assay (IDS RIA kit catalogue AA-35F1; Immunodiagnostics Systems Ltd, Tyne and Wear, UK). The assay consists of a two-stage procedure: extraction of 25-OH vitamin D and other hydroxylated metabolites from serum or plasma, followed by incubation with radioactive labelled iodine (I125) 25-OH vitamin D label and a highly specific 25-OH vitamin D antibody. The bound radioactivity is inversely proportional to the concentration of 25-OH vitamin D. The coefficient of variation of the assay over the period of the investigation was 4.4-5.2%. The IDS RIA kit produces results that can be related to the Diasorin assay by the equation IDS = 0.84 × Diasorin + 5 nmol/l (Information from Immunodiagnostics Systems Ltd). Results will be therefore slightly higher on the Diasorin assay with 50 nmol/l on IDS becoming 53 nmol/l on the Diasorin assay.


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