What is the first step in analyzing a 24-hour urine specimen for quantitative protein?

• A. Subculture the urine for bacteria
• B. Add the appropriate preservative
• C. Screen for albumin using a dipstick
• D. Measure the total volume

Answer: (D)

In this test, the goal is to quantify how much protein is excreted in a full day. The key is that you must convert concentration to a total daily amount, which requires knowing the total urine volume collected. The daily protein excretion equals the protein concentration times the total volume of urine collected over 24 hours. Once you have the volume, you measure the protein concentration in an aliquot and multiply by that volume to get the exact amount excreted in 24 hours. This approach accounts for how dilute or concentrated the urine is, giving an accurate daily burden of protein. Preservatives or bacterial culture steps aren’t what determine the daily protein load, and a dipstick alone won’t provide the complete quantitative 24-hour picture.