The full content of Annals is available to subscribers

Subscribe/Learn More  >
Brief Communications |

Serum Levels of Free 1,25-Dihydroxyvitamin D in Vitamin D Toxicity

John M. Pettifor, MBBCH, PhD; Daniel D. Bikle, MD, PhD; Meropi Cavaleros, MT; Dianne Zachen, MT; Mahomed C. Kamdar, MBBS; and Frederick P. Ross, PhD
[+] Article, Author, and Disclosure Information

From the University of the Witwatersand, Johannesburg, South Africa. The University of California, San Francisco, California. The University of Natal, Durban, South Africa. Requests for Reprints: John M. Pettifor MBBCh, Mineral Metabolism Research Unit, Department of Pediatrics, Baragwanath Hospital, P.O. Bertsham 2013, South Africa. Acknowledgments: The authors thank Dr. I. Jialal, Dr. M.C. Rajput, and Dr. A.R. Seebaran for their assistance and Dr. P.K. Naidoo, medical superintendent of the R.K. Khan Hospital, Chatsworth, South Africa, for permission to publish. Grant Support: By a grant from the South African Medical Research Council.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1995;122(7):511-513. doi:10.7326/0003-4819-122-7-199504010-00006
Text Size: A A A

Objective: To determine the serum level of free 1,25-dihydroxyvitamin D (1,25-[OH]2D) in patients with vitamin D toxicity and to assess the in vitro effect of differing concentrations of vitamin D metabolites on the free serum levels of 1,25-(OH)2D.

Design: 1] A case study of patients hospitalized with vitamin D toxicity after accidentally ingesting a veterinary vitamin D concentrate and 2) an in vitro experiment in which vitamin D metabolites in various concentrations were added to normal serum and their effect was noted on percentage of free 1,25-(OH)2D.

Patients: 11 patients (age range, 8 to 69 years) were studied 10 to 40 days after hospitalization for hypercalcemia.

Measurements: Serum total 25-hydroxyvitamin D (25-OHD) and 1,25-(OH) (2D) levels were measured by radioreceptor assays. The percentage of free 1,25-(OH)2D was measured by centrifugal ultrafiltration isodialysis and was used to calculate actual free 1,25-(OH)2D levels. In the in vitro studies, vitamin D metabolites (25-OHD; 24,25-[OH]2D; 25,26-[OH]2D; and 25-OHD-26,23 lactone) were added to normal serum in concentrations expected to occur with vitamin D toxicity. The percentage of free 1,25-(OH) (2D) was measured by isodialysis.

Results: All patients presented with marked hypercalcemia (mean calcium level, 3.99 ±0.33 mmol/L). Serum 25-OHD levels ranged from 847 to 1652 nmol/L, and total 1,25-(OH)2D levels (mean, 106 ±86 pmol/L) were elevated in only three patients. The percentage of free 1,25-(OH)2D (mean, 1.023% ±0.366%) was elevated in all nine patients in whom it was measured. Actual free 1,25-(OH)2D levels (mean, 856 ±600 fmol/L) were elevated in six of the nine patients. Total 1,25-(OH)2D levels were correlated with 25-OHD levels (r = 0.66; P = 0.03), whereas total and free 1,25-(OH)2D levels were highly correlated (r = 0.957; P < 0.001). In the in vitro studies, the percentage of free 1,25-(OH)2D increased after 25-OHD or 24,25-(OH)2D was added.

Conclusions: Although the patients had normal or near-normal total 1,25-(OH)2D values, most patients had elevated free 1,25-(OH)2D levels. These findings suggest that elevated free 1,25-(OH)2D levels might play a role in the pathogenesis of hypercalcemia in vitamin D toxicity.





Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).


Submit a Comment/Letter
Submit a Comment/Letter

Summary for Patients

Clinical Slide Sets

Terms of Use

The In the Clinic® slide sets are owned and copyrighted by the American College of Physicians (ACP). All text, graphics, trademarks, and other intellectual property incorporated into the slide sets remain the sole and exclusive property of the ACP. The slide sets may be used only by the person who downloads or purchases them and only for the purpose of presenting them during not-for-profit educational activities. Users may incorporate the entire slide set or selected individual slides into their own teaching presentations but may not alter the content of the slides in any way or remove the ACP copyright notice. Users may make print copies for use as hand-outs for the audience the user is personally addressing but may not otherwise reproduce or distribute the slides by any means or media, including but not limited to sending them as e-mail attachments, posting them on Internet or Intranet sites, publishing them in meeting proceedings, or making them available for sale or distribution in any unauthorized form, without the express written permission of the ACP. Unauthorized use of the In the Clinic slide sets will constitute copyright infringement.


Buy Now for $32.00

to gain full access to the content and tools.

Want to Subscribe?

Learn more about subscription options

Related Articles
Topic Collections
PubMed Articles
Forgot your password?
Enter your username and email address. We'll send you a reminder to the email address on record.