Method and reagent for determining vitamin D metabolites

1. A reagent for determining vitamin D, comprising:

i) a vitamin D-releasing agent comprising:

a) at least one hydrotropic substance,

b) at least one transition metal salt, and

c) optionally at least one complexing agent,

wherein the vitamin D-releasing reagent has from 5 to 30 wt. % of the at least one hydrotropic substance and from 0.1 to 5 wt. % of the at least one transition metal salt, based on the total weight of the reagent, in an aqueous fluid; and

(ii) a determination reagent for vitamin D.

2. The reagent according to claim 1 , wherein the hydrotropic substance is an aromatic acid and/or an ester, amide or salt thereof.

3. The reagent according to claim 1 , wherein the transition metal salt is the salt of a metal of group 5, 6, 7, 8, 10 and/or 12.

4. The reagent of claim 1 , wherein the vitamin D-releasing reagent has from 10 to 25 wt. % of the at least one hydrotropic substance and from 0.2 to 2 wt. %, of the at least one transition metal salt, based on the total weight of the reagent, in an aqueous fluid.

5. The reagent according to claim 1 , wherein the hydrotropic substance is N,N-dimethylbenzamide, dimethylbenzoic acid, 1,2-naphthoquinonesulfonic acid, para-toluenesulfonic acid, sulfanilic acid, anthraquinone-2-sulfonic acid, aniline-2-sulfonic acid and/or a salt thereof.

6. The reagent according to claim 1 , wherein the hydrotropic substance is toluenesulfonic acid and/or an ester, amide or salt thereof.

7. The reagent according to claim 1 , wherein the transition metal salt is a salt of vanadium, chromium, manganese, iron, cobalt, nickel and/or zinc.

8. The reagent according to claim 1 , wherein the transition metal salt is an iron(III) salt.

9. The reagent according to claim 1 , wherein the transition metal salt is iron(III) chloride or iron(III) citrate.

10. The reagent according to claim 1 , further comprising a labelled form of vitamin D as a tracer.

11. The reagent according claim 1 , wherein the determination reagent for vitamin D comprises an immunological binding partner for vitamin D.

12. The reagent according to claim 11 , wherein the immunological binding partner for vitamin D is a receptor or an antibody for vitamin D.

13. An in vitro method for releasing vitamin D by a reagent according to claim 1 , comprising the steps of:

a) bringing a sample that contains bound vitamin D into contact with the vitamin D-releasing agent, and

b) releasing the bound vitamin D.

14. The method according to claim 13 , wherein the sample is a biological fluid which is blood, serum, plasma or milk.

15. The method according to claim 13 , wherein the hydrotropic substance is an aromatic acid and/or an ester, amide or salt thereof.

16. The method according to claim 13 , wherein the transition metal salt is the salt of a metal of group 5, 6, 7, 8, 10 and/or 12.

17. The method according to claim 13 , wherein the release reagent further contains a complexing agent.

18. The method according to claim 13 , wherein the release reagent is added to the sample in an amount to give a final concentration of from 200 to 1000 mM of the hydrotropic substance and/or a final concentration of from 5 to 100 mM of the transition metal salt.

19. The method according to claim 13 , wherein the vitamin D is 25-hydroxy vitamin D3, 25-hydroxy vitamin D2, 1,25-dihydroxy vitamin D3, 1,25-dihydroxy vitamin D2, vitamin D3, vitamin D2 or a mixture thereof.

20. An in vitro method for determining vitamin D by a reagent according to claim 1 , comprising the steps of:

a) bringing a sample that contains bound vitamin D into contact with the vitamin D-releasing agent,

b) releasing the bound vitamin D, and

c) determining the released vitamin D.

21. The method according to claim 20 , wherein vitamin D is determined without separating off the release reagent.

22. The method according to claim 20 , wherein the concentration of vitamin D is determined in step c) by an immunological method.