Why is a first-morning urine sample often preferred for assessing proteinuria?

• A. It is more concentrated and reduces variation in concentration due to hydration
• B. It is less contaminated
• C. It yields more glucose
• D. It is more acidic

Answer: (A)

The main idea is that urine protein measurements are affected by how concentrated or dilute the urine is. Overnight, people usually drink less and produce less urine, so the first-morning sample is more concentrated. A concentrated sample makes protein easier to detect and quantify and also reduces the day-to-day variation caused by how hydrated a person is, posture, and recent activity. This gives a more reliable snapshot of baseline protein excretion. Morning collection also tends to minimize the effect of orthostatic proteinuria, which can raise protein levels later in the day when a person is upright. So, the first-morning urine provides a stable, representative measure of proteinuria. Contamination, glucose content, or acidity aren’t the main reasons for preferring this sample.