Proteases break peptide bonds in proteins to release the building blocks of proteins, amino acids. In digestion, proteins are first cleaved into smaller peptides, but these are then further degraded by other enzymes into free amino acids that can be absorbed by the intestinal lining. Nucleotides come from nucleic acids, not proteins. Peptides are intermediate products, not the final digestion products. Glucose comes from carbohydrate digestion. Therefore, the final digestion product of proteins by protease is amino acids.

A monoclonal protein spike on serum protein electrophoresis signals a monoclonal gammopathy, meaning a single clone of plasma cells or B cells is producing a uniform immunoglobulin. This finding is important because it points toward plasma cell–related disorders such as MGUS or multiple myeloma, and it triggers specific follow-up tests to characterize the protein and guide further clinical workup. Immunofixation electrophoresis is performed to identify the precise heavy and light chain of the monoclonal protein (for example, IgG kappa), along with additional assessments like quantitative immunoglobulins and free light chains, and often imaging or bone marrow evaluation if a malignant process is suspected. It does not indicate bacterial infection or liver failure, and rather than ruling out plasma cell disorders, it prompts targeted evaluation for them.

A multitarget stool DNA test is designed to detect colorectal cancer by combining DNA methylation markers with occult blood testing, boosting the signal from cancer in stool. The figure most often reported for its ability to detect colorectal cancer is about 92% sensitivity, meaning it correctly identifies roughly 92 of 100 cancers in screening populations. This level of sensitivity is higher than many single-marker stool tests, though the test’s specificity sits in the mid-80s, so there are some false positives. So the commonly cited accuracy for detecting colorectal cancer with this test is 92%.

Elimination through the hepatic and biliary pathways refers to how substances are processed by the liver, secreted into bile, and then carried into the intestine to be excreted in the stool. This route is distinct from renal excretion (into urine), exhalation (through the lungs for volatile substances), or sweat (through skin). The liver conjugates and secretes certain substances into bile via transporters, so larger or more polar compounds end up in the feces after biliary excretion. Sometimes these substances can undergo enterohepatic recirculation, but the end result is elimination in stool.

Screening with serology is done first because antibody testing is noninvasive, sensitive, and helps decide whether invasive confirmation is needed. The most useful initial test is a tissue transglutaminase IgA (tTG-IgA) assay, ideally with a check of total IgA to catch any IgA deficiency that could mask a positive result. A positive serology result strongly indicates celiac disease and leads to confirmation by an intestinal biopsy obtained during upper endoscopy, which shows the characteristic villous atrophy and crypt changes. If IgA deficiency is present, IgG-based tests (such as tTG-IgG or DGP-IgG) are used instead. Gluten challenge is not the first step; it’s reserved for specific scenarios where the diagnosis remains uncertain after initial testing or when a patient has been on a gluten-free diet.