Assays for disease-associated crystals in biological samples
Methods of assaying for disease-associated crystal species in biological samples are described. Such methods involve contacting a patient sample with an excess of a detectable crystal-tagging compound reactive with a plurality of crystal species under conditions that allow the detectable crystal-tagging compound to react with a plurality of crystal species, if present, to form tagged crystal species complexes. Substantially all unreacted tagging compound is then removed. If desired, chemical, enzymatic, or physical treatment can be used to selectively degrade some, but not, of the tagged crystal species. Assessment of soluble versus crystal-associated label is then performed.
1. A method of assaying for crystallized calcium pyrophosphate dihydrate (CPPD) in a biological sample, comprising:
(i) contacting a biological sample from a patient with an excess of a detectable calcium crystal-tagging compound reactive with a plurality of crystallized calcium species under conditions that allow the detectable calcium crystal-tagging compound to react with any crystallized calcium species present in the biological sample to form detectable crystallized calcium complexes, wherein the detectable calcium crystal-tagging compound is radiolabeled phosphocitrate;
(ii) removing substantially all unreacted detectable calcium crystal-tagging compound;
(iii) contacting the detectable crystallized calcium complexes with a reagent that selectively degrades CPPD to release a soluble detectable species, wherein (x) the reagent that selectively degrades CPPD is a pyrophosphorylase or pyrophosphatase and (y) the soluble detectable species is dissolved mineral containing the radiolabel; and
(iv) detecting the soluble detectable species, thereby detecting the presence of CPPD in the biological sample.
2. A method according to claim 1 , wherein the biological sample is a fluid sample.
3. A method according to claim 2 , wherein the fluid sample is a sample of synovial fluid.
4. A method according to claim 1 , wherein the detection step is qualitative, semi-quantitative, or quantitative.
5. A method according to claim 1 , wherein the reagent that selectively degrades CPPD to release a soluble detectable species is a pyrophosphorylase.
6. A method according to claim 1 , wherein the radiolabel is selected from the group consisting of 111 In, 99 Tc, 14 C, 131 I, 125 I, 3 H, 32 P, and 35 S.