Which screening test requires a 12-hour fast before testing?

Which screening test requires a 12-hour fast before testing?

• A. Total cholesterol
• B. Serum lipid profile
• C. Serum chemistry profile
• D. Hematocrit

Answer: (B)

The key idea is that lipid measurements are affected by recent meals. After eating, triglycerides rise and can skew the results used to calculate LDL cholesterol, which is why a fasting sample is used for lipid screening. A 12-hour fast helps bring triglyceride levels down to baseline, giving a more accurate lipid profile and a clearer view of cardiovascular risk in the pediatric patient. The other tests are not routinely based on fasting: total cholesterol alone can be obtained without fasting, a hematocrit is a simple blood count not dependent on meal timing, and a serum chemistry profile may or may not require fasting depending on which components are being evaluated.

The key idea is that lipid measurements are affected by recent meals. After eating, triglycerides rise and can skew the results used to calculate LDL cholesterol, which is why a fasting sample is used for lipid screening. A 12-hour fast helps bring triglyceride levels down to baseline, giving a more accurate lipid profile and a clearer view of cardiovascular risk in the pediatric patient. The other tests are not routinely based on fasting: total cholesterol alone can be obtained without fasting, a hematocrit is a simple blood count not dependent on meal timing, and a serum chemistry profile may or may not require fasting depending on which components are being evaluated.