Heaney measured calcium density in stool in order to monitor calcium intake in patients. This can help identify a patient who may be noncompliant in taking calcium supplements. The author is from Creighton University in Omaha, Nebraska.


A standard calcium supplement tablet contains 12.5 mmol calcium. The amount of calcium absorbed is relatively low, with most of a daily dose appearing in the stool.


Specimen: The study used 4 days of pooled fecal samples. However, the author found that the rate of excretion was relatively constant so that a smaller interval could be used.



(1) fecal calcium density (calcium in mmol per gram dry weight feces)


calcium intake in mmol per day =

= (26.75 * (fecal calcium density)) + 0.626


The author also gave an equation for estimating fecal calcium density based on daily calcium intake:


fecal calcium density =

= (0.0301 * (calcium intake in mmol/day)) + 0.114


If this equation is re-arranged:


calcium intake in mmol/day =

= (33.22 * (fecal calcium density)) - 3.787



• The study assumed constant calcium intake. The equation should work for a person who is always compliant or always noncompliant, but it might not work for a person who is intermittently so.

• The technique is dependent on the accuracy of the measurement. A small change in the fecal calcium density can result in a large change in the estimated intake. The stool sample has to be dried to the same degree each time.


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