False-positive meconium screen [letter].

The BM meconium test is a useful screening test for cystic fibrosis. 
However, we have had false-positive results in two babies caused by 
the use of rectal glycerin suppositories. The babies presented with signs 
suggestive of intestinal obstruction possibly due to meconium ileus, and glycerin 
suppositories were inserted to speed the passage of meconium so that 
the BM test could be done to help confirm the diagnosis. 
The tests were positive but the babies were subsequently shown not 
to have cystic fibrosis, and we found that the glycerin suppositories 
themselves produce the typical blue colour on the test strip. 