Immunohistochemistry on Paraffin-Embedded Sections (CST Demo)

critical

False negative — no staining at all

Even the positive control shows no staining; expected positive regions are completely blank; the experiment failed.

💡 4 · ✓ 4

critical

False-Positive Signal from Endogenous Enzyme Activity

High background signal observed when using enzyme-conjugated antibodies (HRP or AP), caused by endogenous alkaline phosphatase or peroxidase activity in tissue generating false-positive results.

💡 4 · ✓ 4

critical

Mouse-on-Mouse Cross-Reactivity in Tissue Staining

High background when using mouse primary antibodies on mouse tissue, caused by secondary antibody binding to endogenous mouse immunoglobulins and Fc receptors rather than only the primary antibody.

💡 4 · ✓ 4

critical

Complete Absence of IHC Staining

Complete lack of staining observed in immunohistochemistry experiment despite using validated antibody. Tissue sections appear negative even when positive control should show signal.

💡 6 · ✓ 6

severe

Abnormal nuclear staining (wrong subcellular localization)

Cell nuclei show strong staining when they shouldn't, or expected positive nuclei show no staining; nuclear/cytoplasmic localization is wrong.

💡 4 · ✓ 4

severe

High Background from Insufficient Non-Specific Blocking

Diffuse background staining observed throughout tissue sections in IHC experiments, indicating inadequate blocking of non-specific antibody binding sites.

💡 4 · ✓ 4

severe

Over-Amplified Signal with Biotin-Based Detection Systems

Excessive background staining when using amplification techniques or biotin-based detection, either from high signal amplification or endogenous biotin binding to streptavidin/avidin.

💡 4 · ✓ 4

severe

High Background from Excessive Antibody Concentrations

Elevated background staining throughout tissue sections due to excessively high concentrations of primary or secondary antibodies leading to non-specific binding.

💡 4 · ✓ 5

severe

Antibody not validated for IHC application or tissue type

Complete absence of staining with antibody that works in other applications. The antibody may not recognize native protein conformation present in tissue sections.

💡 4 · ✓ 5

severe

Incorrect Antibody Diluent Selection

Suboptimal signal intensity or background issues despite correct antibody concentration. Different antibodies show dramatically different performance in TBST/5% NGS versus SignalStain Antibody Diluent.

💡 3 · ✓ 3

severe

Mouse-on-Mouse (MOM) Background

High background staining when using mouse primary antibody on mouse tissue. Secondary antibody binds endogenous mouse IgG throughout the tissue, creating non-specific signal.

💡 3 · ✓ 4

severe

Strong positive background / non-specific staining

Whole slide appears brown/diffuse stained; negative control also shows signal; impossible to distinguish true positive signal.

💡 5 · ✓ 5

severe

Autofluorescence from Formaldehyde-Based Fixatives

High fluorescent background signal when using formaldehyde-based fixatives (formalin/PFA) with fluorescent detection, particularly at green wavelengths where these fixatives naturally fluoresce.

💡 4 · ✓ 4

severe

Residual Reagent Background from Inadequate Washing

Elevated background signal caused by residual fixative or unbound antibodies remaining on tissue sections between procedural steps, producing false-positive staining.

💡 5 · ✓ 5

severe

Target protein absent or below detection threshold in tissue

No staining observed in experimental tissue samples. The target protein may not be expressed in the tissue type or developmental stage being examined, or present at undetectable levels.

💡 4 · ✓ 6

severe

Formaldehyde fixation masked epitopes preventing antibody binding

No staining in formaldehyde-fixed tissues despite validated antibody. Fixation-induced protein crosslinking masks epitopes and prevents antibody recognition.

💡 4 · ✓ 5

severe

Weak or Suboptimal IHC Staining Intensity

Staining signal is present but significantly weaker than expected, with poor contrast between positive cells and background, making interpretation difficult.

💡 5 · ✓ 5

severe

Antigen Retrieval Method Not Optimized for Target

Staining results are inconsistent or suboptimal despite correct antibody and detection system, with signal strength varying significantly based on retrieval method used.

💡 4 · ✓ 4

severe

Inadequate Detection System Sensitivity

Weak signal or no staining despite proper primary antibody performance. Standard HRP-conjugated secondary antibodies fail to provide sufficient signal amplification.

💡 4 · ✓ 4

severe

Suboptimal Antigen Retrieval Method Selection

Weak or absent staining despite proper antibody concentration and incubation. Clear performance differences observed when comparing different antigen retrieval heating methods.

💡 4 · ✓ 4

moderate

Non-Specific Binding from Elevated Incubation Temperature

Increased background staining when primary antibody incubation is performed at room temperature, as higher temperatures promote non-specific antibody-tissue interactions.

💡 4 · ✓ 4

moderate

Edge Artifacts from Tissue Section Drying

Higher background staining concentrated at the edges of tissue sections compared to the center, indicating tissue dehydration during the staining procedure.

💡 4 · ✓ 5

moderate

Nuclear protein not detected due to insufficient permeabilization

No staining observed when targeting nuclear proteins. Antibody cannot access nuclear compartment despite proper antibody concentration and incubation time.

💡 3 · ✓ 4

moderate

FFPE tissue shows no staining from incomplete deparaffinization

Paraffin-embedded tissue sections show no immunostaining. Residual paraffin creates a physical barrier preventing antibody access to tissue antigens.

💡 3 · ✓ 4

moderate

Weak or absent signal from inadequate antibody concentration or incubation

No detectable staining despite proper protocol execution. Insufficient antibody-antigen binding due to suboptimal concentration or incubation conditions.

💡 4 · ✓ 5

moderate

Primary-secondary antibody incompatibility preventing detection

No signal detected despite proper primary antibody binding. Secondary antibody fails to recognize or bind to the primary antibody, breaking the detection chain.

💡 4 · ✓ 5

moderate

Spotty or Uneven Background Staining Pattern

Staining pattern shows irregular, patchy, or spotty background with uneven distribution across tissue sections, indicating technical artifacts rather than biological variation.

💡 3 · ✓ 3

moderate

High Background Staining in IHC

Excessive background signal obscuring specific staining. Non-specific binding observed throughout tissue sections, making interpretation difficult.

💡 5 · ✓ 5

moderate

Incorrect Antibody Diluent Selection

Staining quality is significantly reduced or inconsistent when using generic diluent instead of product-specific recommended diluent, as different antibodies perform optimally in different buffer compositions.

💡 3 · ✓ 4

moderate

Insufficient Detection System Sensitivity

Signal is weak or undetectable despite correct antibody and protocol, particularly for low-abundance targets, indicating that the detection system lacks sufficient signal amplification.

💡 3 · ✓ 4

moderate

Inadequate Washing Steps Causing Poor Contrast

High background persists with poor contrast between positive signal and background despite other optimization steps, making interpretation difficult.

💡 4 · ✓ 4

moderate

Endogenous Biotin Interference

High background staining specifically in kidney, liver, or other biotin-rich tissues when using biotin-based detection. Background not resolved by standard blocking procedures.

💡 3 · ✓ 3

moderate

Edge effect / uneven staining across the slide

Slide edges show darker staining than center, or one half stains more than the other; reproducibility between fields is poor.

💡 4 · ✓ 4

moderate

Loss of membrane protein staining after permeabilization

No staining is detected when targeting membrane proteins in IHC. Signal is absent despite antibody validation, suggesting structural damage to membrane epitopes.

💡 3 · ✓ 4

moderate

Suboptimal Primary Antibody Incubation

Inconsistent or weak staining results despite following protocol. Staining intensity varies between experiments using same antibody lot and tissue type.

💡 3 · ✓ 3