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What You Need To Know About Calcium In Urine Tests

Calcium in urine tests can help determine bone loss and whether your bone breakdown process is normal. It can also help you to determine if your bone-building program is effective.

Bones are living, growing tissue that is constantly being renewed during our lifetime. Bone remodeling (the removal of old bone and replacement with new bone) occurs in two phases:

  • Resorption: Cells called osteoclasts dissolve tissue on the bone's surface, creating a small cavity.
  • Formation: Cells called osteoblasts fill the cavities with new bone

If the bone removed by resorption is completely replaced, then the amount of bone does not change and bone strength is maintained. A calcium in urine test is helpful in assessing whether too much resorption (bone loss) is taking place compared to bone formation, which could lead to osteoporosis.

CALCIUM IN URINE TESTS

The two most widely used urine tests (also known as bone resorption markers) are the Dpd (deoxypyridinoline crosslinks) and the NTx (N-telopeptides) tests. The CTX (c-telopeptides) Osteomark test may be conducted either as a urine or a blood test although many physicians are now favoring use of the blood test.

The standard laboratory range for these tests is large, so many experts choose an optimal level within the acceptable range. As a healthy average for pre-menopausal women is around 36 (bone collagen equivalent units/mmol creatinine) many experts choose the high 30s or low 40s as an ideal level. The desired level for the Dpd test is often set in the 4s or a low 5.

In addition to the NTx and Dpd, a 24-hour urine calcium excretion test may be used to test whether the body is too acidic. For this test, all of the patient's urine must be collected over a 24 hour period for submission to laboratory analysis.

THE TESTING PROCESS

Calcium in urine tests can show a substantial day-to-day variation, so many experts require samples over a two day period. A typical sampling procedure might include the following steps:

Getting Ready

Avoid vitamin supplements (and especially vitamin C) the day before your first sample and during your two sample days.

Day 1

  • Do not take any vitamins, food, or coffee before collecting your urine sample. (Taking a thyroid pill is okay.)
  • Urinate as usual in the morning but do not save the urine.
  • Drink 1-2 cups of water.
  • Collect a urine sample in a clean plastic or glass container prior to 10 a.m. and refrigerate it.

Day 2

Repeat the steps from Day 1. Then mix half of each day's urine in a third container. Write your name and the date on this container prior to taking it to the laboratory and discard the leftover urine. Don't forget to refrigerate the urine sample until you take it to the lab... and put it into a paper bag to avoid sunlight exposure.

TIP: It is easiest to follow these instructions if you take the first sample on Sunday and the second on Monday.

Calcium in urine tests are generally conducted in-between bone density scans to assess the effectiveness of a bone building program. They are not an accurate indicator of osteoporosis risk in isolation and some physicians do not support their use because of the large variations in calcium levels throughout the day and as a result of food intake.

To learn about supplements that minimize calcium in urine by optimizing absorption into the bones... visit Osteoporosis Treatment Guidelines.