External Quality Assessment in Histopathology and IHC

External quality assessment (EQA) in histopathology and immunohistochemistry (IHC) is an independent evaluation of the quality of tissue preparations and the accuracy of morphological diagnosis. Proficiency testing programs cover the entire workflow, from tissue fixation and processing to IHC staining and interpretation of results. In the era of targeted cancer therapy, the quality of IHC testing determines the choice of treatment.

The Importance of EQA in Anatomic Pathology

Histopathology and IHC are the areas where the subjective component of diagnosis is greatest. The pathologist's morphological report determines the diagnosis, the disease stage and the treatment strategy. The quality of tissue preparations and the intensity and specificity of IHC reactions directly affect the accuracy of interpretation.

Why EQA is critical:

• IHC determines the choice of therapy: HER2, PD-L1 and ER/PR status in breast cancer; the prescription of targeted drugs depends on the result
• Pre-analytical variability: fixation time, fixative type and processing protocol all affect IHC quality
• Interlaboratory differences: up to 20% discordance in HER2 status assessment between laboratories that do not participate in EQA
• Subjective interpretation: morphological assessment depends on the pathologist's expertise
• Regulatory requirements: GOST R ISO 15189-2024 (the Russian national adoption of ISO 15189), ASCO/CAP guidelines for HER2 and PD-L1

EQA Areas in Histopathology

Quality of Tissue Preparations

• Fixation: assessment of fixation adequacy (10% neutral buffered formalin, 6–72 hours)
• Tissue processing: quality of dehydration, clearing and paraffin infiltration
• Microtomy: section thickness and absence of artifacts
• H&E staining: intensity, contrast and preservation of detail
• Special stains: PAS, Masson's trichrome, Congo red, Perls' iron stain

Immunohistochemistry

• Diagnostic markers: cytokeratins (CK7, CK20, CK5/6), vimentin, CD45, S-100
• Prognostic markers: Ki-67, p53, ER, PR
• Predictive markers: HER2, PD-L1, ALK, ROS1, MSI/MMR
• Hematopathology: CD3, CD20, CD30, CD10, BCL2, BCL6, MUM1

Morphological Interpretation

• Consensus diagnosis: assessment of the accuracy of the histological report
• Tumor grading: reproducibility of differentiation grade assessment
• Surgical margin assessment: completeness of resection

International EQA Programs

NordiQC: The Gold Standard of IHC Quality Control

NordiQC (Nordic Immunohistochemical Quality Control) is the recognized global leader in external quality assessment for IHC. Key features:

• More than 90 antibodies in the assessment program
• Detailed feedback: each slide is scored on a standardized scale (Optimal, Good, Borderline, Poor)
• Protocol recommendations: specific optimization recommendations are provided after an unsatisfactory result
• Database of optimal protocols: access to validated protocols for all major IHC platforms

Equipment Compatibility

IHC Quality Assessment Criteria

The NordiQC Scale

What Is Assessed

• Sensitivity: detection of true-positive cells
• Specificity: absence of false-positive staining
• Background staining: clean background with no artifacts
• Controls: presence and adequacy of positive and negative controls
• Intensity: consistency with the expected staining pattern

Practical Recommendations

EQA Participation Strategy

1. Mandatory minimum: NordiQC for all IHC antibodies in use; this is the global standard

2. For oncology laboratories: add CAP IHC (HER2, ER/PR, PD-L1) and UK NEQAS ICC

3. For morphological diagnosis: CAP Surgical Pathology + ESP EQA

4. For histotechnology: staining quality control (H&E, special stains) through CAP or ESP

5. For continuing education: CAP educational programs (PIP, NGC, PAP Education, HistoQIP) with CME credit for pathologists and CE credit for staff

Working with NordiQC Results

• After a "Borderline" or "Poor" score, switch immediately to the protocol recommended by NordiQC
• Use the NordiQC database to select optimal antibody clones and dilutions
• Keep an IHC validation log linked to EQA results

Pre-Analytics: The Foundation of Quality

• Standardize fixation time: 6–72 hours in 10% neutral buffered formalin
• Monitor warm ischemia time, from tissue removal to placement in fixative
• Keep a log of pre-analytical parameters for each block

EQA Is a Chance to Learn: CAP Education and Competency Programs

Every EQA round is also a training case. The pathologist examines the slide like a patient case, submits a diagnosis and then sees the intended answer, the peer results and, in the educational programs, a discussion of each case. That turns external quality assessment into continuing education for the whole team: participate, learn and claim CME credit.

The College of American Pathologists (CAP) runs the broadest set of such programs in anatomic pathology, cytopathology, histotechnology and molecular pathology:

What the Credit Is Worth

Cytotechnologists can apply credit from the CAP cytopathology programs toward the continuing-education requirements of their professional bodies, and Surveys participants can claim CE credit at no extra charge through a free CAP web account (CAP catalogue 2024).

Whether CME or CE credit counts toward a national licence or recertification is decided by each country's licensing body, so ask yours which credits it recognizes. For a laboratory preparing for accreditation, documented participation is also evidence of staff competency, which both ISO 15189 and the CAP checklists require. More: how CAP EQA trains the laboratory team and Accreditation – CAP LAP and ISO norms.

KombiMED's Comprehensive Approach

KombiMED supplies the full range of equipment for anatomic pathology laboratories, from tissue processors and microtomes to automated IHC stainers (Roche Ventana BenchMark ULTRA, Leica BOND) and staining systems (Sakura Tissue-Tek, Leica ST5020). We also arrange enrollment in international EQA programs for histology and IHC.

Our specialists can help you:

Request a consultation on external quality assessment for your pathology laboratory.

In more depth in our EQC guide: EQA programmes by discipline, how IHC results are graded, EQA providers compared and Accreditation – CAP LAP and ISO norms.

• Select EQA programs for IHC, special stains and morphological diagnosis
• Select CAP educational and competency programs for pathologists and histotechnologists, with CME and CE credit
• Optimize IHC protocols based on NordiQC recommendations
• Prepare your laboratory for GOST R ISO 15189-2024 accreditation for morphological testing

Frequently Asked Questions