Measurement of serum lipoproteins
View Patent ↗Although a more accurate estimate of a person's risk of cardiovascular disease can be made on the basis of the number of lipoprotein particles per unit volume in the person's blood, current methods all rely on measuring the mass of lipoprotein cholesterol per unit volume. It has been discovered that a rapid and accurate lipoprotein particle count can be obtained by photometry. A method and apparatus are provided for measuring the number of lipoprotein particles in a sample using photometry.
1. A method of measuring lipoprotein particle number in a sample, the method comprising:
a. separating a LDL fraction, an IDL fraction and a VLDL fraction in the sample by centrifugation;
obtaining a photometric measurement in the LDL fraction;
c. calculating a LDL particle count for the LDL fraction that is a function of the photometric measurement;
d. obtaining a photometric measurement in the IDL fraction;
e. calculating an IDL particle count for the IDL fraction that is a function of the photometric measurement in the IDL fraction;
f. obtaining a photometric measurement in the VLDL fraction;
g. calculating an VLDL particle count for the VLDL fraction that is a function of the photometric measurement in the VLDL fraction;
h. separating at least one additional lipid fraction in the sample by centrifugation, the at least one additional lipid fraction selected from the group consisting of: a Lp(a) fraction and an HDL fraction;
i. obtaining a photometric measurement in the at least one additional lipid fraction; and
j. calculating a particle count for the at least one additional lipid fraction, wherein the particle count is a function of the photometric measurement in the at least one additional lipid fraction.
2. The method of claim 1 , wherein the at least one additional lipid fraction is, an Lp(a) fraction.
3. The method of claim 1 , wherein the at least one additional lipid fraction is a HDL fraction.
4. The method of claim 1 , wherein the at least one additional lipid fraction is an Lp(a) fraction and an HDL fraction.
5. The method claim 1 , wherein the function is an approximately linear function.
6. The method of claim 1 , wherein separation is accomplished using density-gradient centrifugation.
7. The method of claim 1 , wherein the sample is contained in a sample vessel, and further comprising sampling the sample vessel from the bottom so as to collect the fractions in descending order of density.
8. The method of claim 7 , in which the LDL measurement is obtained before the IDL measurement is obtained, and in which the VLDL measurement is obtained after the LDL measurement is obtained.
9. The method of claim 1 , wherein the sample is selected from the group consisting of: a blood sample and a blood serum sample.
10. A method of measuring lipoprotein particle number in a sample, the method comprising:
a. separating an LDL fraction, an HDL fraction, an Lp(a), an IDP fraction and a VLDL fraction from the sample by centrifugation;
b. obtaining a photometric measurement in the LDL fraction;
c. calculating an LDL particle count for the LDL fraction that is a function of the photometric measurement in the LDL fraction;
d. obtaining a photometric measurement in the HDL fraction;
e. calculating an HDL particle count for the HDL fraction that is a function of the photometric measurement in the HDL fraction;
f. obtaining a photometric measurement in the Lp(a) fraction;
g. calculating an Lp(a) particle count for the Lp(a) fraction that is a function of the photometric measurement in the Lp(a) fraction;
h. obtaining a photometric measurement in the IDL fraction;
i. calculating an IDL particle count for the IDL fraction that is a function of the photometric measurement in the IDL fraction;
k. obtaining a photometric measurement in the VLDL fraction; and
l. calculating an VLDL particle count for the VLDL fraction that is a function of the photometric measurement in the VLDL fraction.
11. The method claim 10 , wherein the function is an approximately linear function.
12. The method of claim 10 , wherein separation is accomplished using density-gradient centrifugation.
13. The method of claim 10 , wherein the sample is contained in a sample vessel, and comprising sampling the sample vessel from the bottom so as to collect the fractions in descending order of density.
14. The method of claim 13 , in which the Lp(a) measurement is obtained after the HDL measurement is obtained, in which in which the LDL measurement is obtained after the Lp(a) measurement is obtained, in which the IDL measurement is obtained after the LDL measurement is obtained, and in which the VLDL measurement is obtained after the IDL measurement is obtained.
15. The method of claim 10 , wherein the sample is selected from the group consisting of: a blood sample and a blood serum sample.