What is a Trichrome Stain?
A trichrome stain is a histological staining technique used in pathology to visualize and differentiate connective tissue components, particularly collagen and muscle fibers, by staining them in contrasting colors—typically collagen appears blue or green, muscle fibers appear red, and nuclei appear dark blue or black. 1
Primary Applications in Medical Pathology
Trichrome staining serves several critical diagnostic purposes:
Connective tissue visualization: The stain specifically highlights collagen fibers and other structural proteins, making it essential for evaluating fibrosis and tissue architecture 1
Bone marrow fibrosis grading: In myeloproliferative neoplasms, trichrome staining is specifically recommended when bone marrow shows grades MF-2 or MF-3 fibrosis to better assess the extent of collagen deposition 1
Cardiac tissue evaluation: In endomyocardial biopsies, elastic trichrome stain (or Movat stain) is routinely used alongside hematoxylin and eosin to visualize collagen and elastic tissue, particularly when evaluating for myocarditis 1
Technical Characteristics
The staining methodology involves multiple dyes applied sequentially:
Modified Mallory-Cason trichrome: This variant discriminates between bone, cartilage, and connective tissue, with bluish staining indicating rich collagen content 1
Tissue preparation requirements: Specimens must be properly fixed (typically in 10% neutral buffered formalin), processed through alcohol gradients, embedded in paraffin, and sectioned before staining 1
Clinical Context and Interpretation
When interpreting trichrome-stained sections, the intensity and distribution of blue/green collagen staining directly correlates with the degree of fibrosis present. 1
In myelofibrosis, the presence of "coarse bundles of thick fibers consistent with collagen" on trichrome stain confirms advanced fibrosis (MF-3 grade) and often indicates osteosclerosis 1
The stain helps distinguish between reticulin fibers (fine network) and mature collagen (thick bundles), which has prognostic implications 1
Important Caveats
Staining variability: Trichrome stains can show batch-to-batch variation depending on dye source, manual versus automated processing, and fixation quality—always include control sections in each staining batch to ensure consistency 1
Processing artifacts: Improper fixation temperature or inadequate tissue handling can create artifacts that mimic or obscure true collagen deposition 1
Not for routine screening: Trichrome staining is a specialized technique ordered when specific assessment of connective tissue is clinically indicated, not part of standard H&E evaluation 1