Comparison of polyethylene glycol and chromium-51 chloride as nonabsorbable stool markers in calcium balance studies.

The day-to-day variations in stool calcium content during calcium balance studies are usually corrected for by adjusting for the recovery of an orally administered nonabsorbable stool marker. We describe here a simple method for making this correction using chromium-51 chloride hexahydrate (51Cr) in balance studies. This approach was developed because of difficulties encountered with the more widely used marker, polyethylene glycol (PEG). With one batch of PEG, the stool recovery was only 81% (whereas with 51Cr it was 95%). The reason for this poor recovery was contamination of the PEG 4000 with a high molecular weight species (10-15%, wt/wt). Because others have also reported low PEG recoveries and because we found that the chemical abnormality in the PEG was very difficult to detect, we believe that 51Cr is more reliable and should be the preferred stool marker for the calcium balance studies.