What distinguishes a positive result in lipid testing?

A positive result in lipid testing is distinguished by a colour change, typically to a red or orange hue.

Lipid testing, also known as a lipid profile or lipid panel, is a group of tests that measure the amount of certain fats and cholesterol in your blood. These tests are used to determine the risk of developing heart disease. The tests typically measure total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), and triglycerides.

In a laboratory setting, lipids can be tested using several methods. One common method is the Sudan III test. Sudan III is a red dye that is soluble in lipids but not in water. When added to a test sample, if lipids are present, they will dissolve the Sudan III dye, resulting in a colour change to red. This is a positive result indicating the presence of lipids.

Another method is the grease-spot or brown paper test. In this test, a sample is placed on a piece of brown paper. If lipids are present, they will leave a translucent spot on the paper even after it has dried. This is also considered a positive result.

The emulsion test is another common method for testing lipids. In this test, the sample is mixed with ethanol, then water is added. If lipids are present, they will form a milky emulsion. The appearance of this milky emulsion is a positive result.

IGCSE Biology Tutor Summary: A positive result in lipid testing is shown by a visible change, such as turning red when using Sudan III dye, leaving a translucent spot on brown paper, or forming a milky emulsion in water and ethanol. These changes indicate the presence of lipids and help assess the risk of heart disease by measuring fats and cholesterol in the blood.