Method and kit for quantitatively determining small, dense LDL cholesterol
A method for fractional measurement of small, dense LDL, which is adaptable for an autoanalyzer, and a reagent for measurement, are provided, making it possible to conduct rapid and convenient analysis with good sensitivity without pretreatment of a specimen. The method for quantitatively determining small, dense LDL cholesterol in a sample comprises the steps of: (1) eliminating cholesterol in LDL other than small, dense LDL in the presence of phospholipase; and (2) quantitatively determining cholesterol in lipoproteins remaining in step (1) above.
1. A kit for quantitatively determining small, dense LDL cholesterol, comprising:
(i) a reagent composition for eliminating cholesterol in LDL other than small, dense LDL in a sample, containing at least sphingomyelinase that reacts with LDL other than small, dense LDL; and
(ii) a reagent composition for measurement of small, dense LDL, containing:
(a) a surfactant that is a polyoxyethylene-polyoxypropylene copolymer that reacts with only small, dense LDL or a derivative thereof; or a surfactant that is a polyoxyethylene derivative with HLB of 11 or more and less than 14;
(b) 4 aminoantipyrine; and
(c) peroxidase.
2. The kit according to claim 1 , further comprising (iii) a reagent composition for eliminating cholesterol in lipoproteins other than LDL, said reagent containing:
(a) a nonionic surfactant selected from the group consisting of at least polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl amine;
(b) an anionic surfactant selected from the group consisting of polyoxyethylene alkylether sulfate, alkyl sulfate, amide ether sulfate, alkyl taurate, and a phosphate-type surfactant;
(c) a cationic surfactant selected from the group consisting of an alkyl methyl ammonium salt, a quaternary ammonium salt, and a mono-linear alkyl type surfactant; or
(d) an amphoteric surfactant selected from the group consisting of lauryl betaine, dimethyl alkyl betaine, an imidazoline type surfactant, and sodium alkyldiaminoethyl glycine.
3. The kit according to claim 1 , wherein the reagent composition (i) further comprises:
(a) a nonionic surfactant selected from the group consisting of at least polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl amine;
(b) an anionic surfactant selected from the group consisting of polyoxyethylene alkylether sulfate, alkyl sulfate, amide ether sulfate, alkyl taurate, and a phosphate-type surfactant;
(c) a cationic surfactant selected from the group consisting of an alkyl methyl ammonium salt, a quaternary ammonium salt, and a mono-linear alkyl type surfactant; or
(d) an amphoteric surfactant selected from the group consisting of lauryl betaine, dimethyl alkyl betaine, an imidazoline type surfactant, and sodium alkyldiaminoethyl glycine, whereby cholesterol in lipoproteins other than small, dense LDL in a sample is eliminated by the reagent composition (i).
4. The kit according to claim 1 , wherein the sphingomyelinase has higher reactivity with at least sphingomyelin than with other phospholipids existing in lipoproteins.