When an age-associated stain becomes a spatial phenotype.

Histochemical staining patterns may vary with age because of changes in cell number, differentiation state, marker expression, tissue geometry, or pre-analytical conditions. Recent data indicate that epithelial tuft-cell abundance decreases and LGR5 immunoreactivity changes in the ageing human colon. We emphasize that marker-positive structures, cell number, and biological function are related but non-equivalent outcomes, particularly for rare epithelial populations and the cellularly complex enteric nervous system. To strengthen interpretation and international reproducibility, we propose a minimum framework combining orthogonal cell-identity markers, transcript-level confirmation in representative samples, donor-level statistical inference, transparent reporting of fixation, staining, imaging, and segmentation variables, and anatomically resolved denominators. A tiered validation pathway could enable laboratories with different technical capacities to generate comparable evidence through standardized bright-field histochemistry, regional multiplex-imaging hubs, and targeted analysis of discordant specimens. This approach could help define age-related staining differences as continuous spatial phenotypes for mechanistic investigation and clinical ageing research.