Low-density lipoproteins (LDL) is a type of lipoprotein that carries cholesterol to the peripheral tissues. LDL-cholesterol is considered bad cholesterol. That means that the greater is the value of LDL, the greater will be the amount of cholesterol in the tissues. High cholesterol in the tissues can lead to heart diseases, obesity, diabetes, and nephrosis.
Everything that I state below will be based on a semi-auto biochemistry analyzer and can depend from one manufacturer to another.
This method does not follow a similar method to HDL-cholesterol, in which the precipitation method was applied. The following method is a two-step method. In the first step, reagent (R1) helps to remove all the non-LDL-cholesterol from the serum. Then, in the second step, there will be a measurement of LDL-cholesterol. This is possible with the help of cholesterol esterase (CHE), cholesterol oxidase (CHOD), and peroxidase (POD). The final product will be the colored quinonimine dye.
The intensity of the dye is directly proportional to the concentration of LDL present in the serum.
Normally, you can store the reagents at 2-80C till the expiration date. But, once you open the bottles, the lifespan of reagents and the working solution will last for about 28 days (at 2-80C).
- Wear an apron and surgical gloves before carrying out the measurement.
- Look for the expiry date of the reagents during purchase and measurement time. Suppliers tend to give you reagent kits with a low expiry interval.
- Bring the reagents and samples to room temperature before you can carry out any measurement.
- Always store reagents in the refrigerator when not in use.
Mix 4 μl of serum/calibrator with 300 μl of reagent (R1). Then, incubate this solution in water or dry bath at 370C for 5 mins. After that, mix 100 μl of reagent (R2). Again, incubate the solution at 370C for 5 mins. Now, sip the incubated solution in the semi-auto biochemistry analyzer and get the result.
In the case of reagent blank, you can mix reagent (R1) and the reagent (R2) in the ratio of 3:1. After that, you can directly into the machine as a reagent blank.
If the concentration of LDL in the serum is very high (out of range) then dilute the solution with 0.9% NaCl or distilled water at the ratio of 1:y. Finally, when you get the result, multiply it with the dilution factor (1+ y).
You will get an increasing slope of this reaction.