Overview of This Medical Test: What It Is, Why It May Be Needed, How It Is Performed, and How You Should Prepare Before Your Appointment

What is this test? This medical test is a clinical evaluation used to help your provider learn more about your symptoms, monitor your health, or guide decisions about treatment and follow-up care.

The 18-hour urine calcium test measures the amount of calcium your kidneys excrete in urine over an 18-hour period. Calcium is an essential mineral important for bone health, nerve function, and muscle contraction. This test helps doctors understand how your body processes calcium and how well your kidneys are working.

How is the test performed? A trained staff member may take a blood sample, collect urine or saliva, swab a body area, or use imaging or physical exam steps. The exact process depends on the test your provider ordered and where you go for care.

You will receive a special container for urine collection. Typically, you start collecting urine in the morning after the first morning void and continue collecting for the next 18 hours, including the first morning void on the second day. It is important to collect all urine during this period for accurate results. The collected urine is then sent to a laboratory for analysis.

How should you prepare for the test? Follow the instructions given to you, such as fasting for a set number of hours, drinking water, avoiding exercise, or discussing current medicines. Ask your provider or lab staff before changing or stopping any prescribed medicine.

Your doctor may ask you to maintain your normal diet for a few days before the test. Continue taking your regular medications unless instructed otherwise. Some medications can affect calcium levels, so inform your doctor about all medications and supplements you are taking. Drink adequate fluids during the collection period unless otherwise advised.