There are several reasons why discordant results could be seen between the 2 split stool samples:
- Homogenization of stool samples in the Lab prior to analysis is used to minimize intra-sample variation, so un-homogenized stool samples split and sent to two different labs will have large variation.
- Stool with hard and lump consistency (Bristol Stool Type 1-2) has more microbial composition variation between different collection sites in a single bowel movement. Therefore samples of different consistency will vary between Labs (e.g., 1 lab received softer/more moist stool particulate matter and other lab received more firm/dry stool particulate matter).
- The outer part of the stool sample will have a different ratio of aerobes/anaerobes because of an oxygen concentration gradient.
- Samples that are loose or watery (Bristol Stool Type 5-7) will have different microbial composition, increased fecal pH, and may cause a false positive for pancreatic elastase-1 (PE-1). Therefore samples of different consistency will vary between Labs.
- Microbiota can vary along with the type and amount of undigested fibers sampled in different aliquots.
- Presence of PCR inhibitors such as complex polysaccharides, bile salts, lipids, uric acid salts, chlorophyll, glycolipids, hemoglobin, and heparin. PCR inhibitors are frequent in stool samples. Un-homogenized stool can have variable PCR inhibitors in the sample which can contribute to false negative PCR results between laboratories.
- Contamination with toilet water or urine will alter bacterial composition and diversity, so if one sample has toilet water or urine and the other does not, it will yield different results.
- Temperature change during shipping and receipt of specimens can account for significant variability. Duration of transportation time may impact microbial growth and decline, and temperature fluctuations are a major stress for bacteria which can cause microbial death and DNA degradation.
