The Importance of the Calcium Load Test

What Is Calcium & Calcium Loading?

Calcium is a chemical mineral used by the body to maintain the strength of bones and teeth. However, this is not the only function of calcium. It is also important in skeletal muscle contraction, and generating the heartbeat. Calcium is also needed to transport substances into and out of a cell. There are many body systems that regulate calcium. The main endocrine system uses the hormones calcitonin and hyperparathyroid hormone to maintain the correct blood levels. The gastrointestinal system will absorb calcium from the food, and the kidneys of the renal system will reabsorb calcium to help maintain blood levels.

When following a reduced calium diet, the calcium load test can be used to see how the digestive, renal, and endocrine systems are able to handle the amount of calcium that is ingested. The physician will be able to monitor the person for any effects of vitamin deficiency or reduced kidney function based on how the body handles an increase in calcium in the system. Calcium loading is a term used to describe the process of giving the body more calcium than what would be normally received in the diet.

Why Is The Calcium Load Test Ordered

This is a test used to determine kidney function by measuring it as a ratio against the amount of calcium excreted. This is done by comparing it to the volume of creatinine excreted by the kidneys. Creatinine is a waste product of metabolism in the muscles digestion. If the blood has high creatinine levels, then this can be an indicator of worsening kidney function.

The test is just a way for the physician to determine if the body is excreting large than normal amounts of calcium into the urine. This condition is called hypercalciuria, and can indicate the potential that other important chemicals are being removed from the body by the kidneys.

How Is The Test Peformed

This test is completed by placing the person on a reduced calcium diet for seven days at no more than 40 milligrams of calcium per day. On the sixth day the person is instructed to empty the bladder in the early morning, and fast two hours for a blood sample to be taken later in the day. The person is next given an increased dose of calcium at one gram and instructed to stop fasting. The person is then told to collect his or her urine over a 24 day process in a special container with the preservative thymol.

Urine Test Results

Test results will show the ratio of calcium levels to creatinine levels within the urine. The ratio of urine calcium to urine creatinine should be below the value of 0.36 during the fasting state. If test results indicate that the ratio after fasting is higher than this, then the person may likely have the condition hypercalciuria. The physician will need to do further endocrine and kidney function tests to confirm the reason for the high level of calcium in the urine.

Another result received from this test is after the calcium load is given. A normal result should have a ratio less than 0.77. However, any ratio higher than this indicates that calcium is also being heavily absorbed by the gastrointestinal system, and being released in the urine. This condition is known as absorptive hypercalciuria, and occurs in 20 percent of the population.


Print Source: Davidson, Stanley & C. Haslett. 2002. "Davidson’s Principles and Practice of Medicine.” Churchill Livingstone, Edinburgh.

Print Source: Cotran R, Kumar V, and Robbins, SL. 1999. Robbins Pathologic Basis of Disease, 6th Ed. W.B. Saunders Company, Philadelphia.

Web Source: Official Journal of American Association of Pediatrics Online. "Urinary Excretion of Calcium Following an Oral Calcium Loading Test in Healthy Children.” 2010. Available:

Web Source: Medic Direct UK. "Calcium Load Test” 2010. Available: