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REVIEW ARTICLE Table of Contents   
Year : 2009  |  Volume : 52  |  Issue : 1  |  Page : 1-5
Quality control in the histopathology laboratory: An overview with stress on the need for a structured national external quality assessment scheme

Consultant Pathologist, Anand Diagnostic Laboratory, No. 11, Blue Cross Chambers, Infantry Road Cross, Bangalore 560 001, India

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The concept of quality control in histopathology is relatively young and less well understood. Like in other disciplines of laboratory medicine, the concept of quality and its control is applicable to pre analytical, analytical and post analytical activities. Assessment of both precision and accuracy performances is possible by appropriate internal and external quality control and assessment schemes. This article is a review of all processes that achieve quality reporting in histopathology. There is a special focus on external quality assessment - a scheme that lacks organization on a national level in our country. Statistical data derived from a small scale external quality assurance program is also analyzed along with recommendations to organize an effective national scheme with the participation of authorized zonal centers.

Keywords: National EQAS, QC histopathology

How to cite this article:
Iyengar JN. Quality control in the histopathology laboratory: An overview with stress on the need for a structured national external quality assessment scheme. Indian J Pathol Microbiol 2009;52:1-5

How to cite this URL:
Iyengar JN. Quality control in the histopathology laboratory: An overview with stress on the need for a structured national external quality assessment scheme. Indian J Pathol Microbiol [serial online] 2009 [cited 2023 Sep 24];52:1-5. Available from:

   Introduction Top

The concept of quality control, which is deeply rooted in most other disciplines of laboratory medicine, is relatively young in the histopathology department. Inherent qualities such as the lack of objective numerical data, descriptive nature of reports, subjectivity, individual judgment and bias, non uniformity of reporting patterns, etc. make assessment and implementation of quality control more difficult in histopathology and a few other disciplines. Modern pathology has ushered in additional methods like immunohistochemistry, morphometry and molecular techniques adding an element of objectivity to the "art and science" of traditional slide interpretation. Medical errors are a significant cause for death and injury. The National Academics Institute of Medicine (IOM) in the U.S.A. estimates that approximately 44,000 to 98,000 deaths occur annually in that country alone due to medical errors. [1] This has prompted joint commission on accreditation of healthcare organization to issue patient safety goals [2] that include patient identification and effective communication among care givers in addition to many others. These goals also apply to the field of histopathology.

Quality control is traditionally applicable to three phases of operation 1) the pre-analytical phase, 2) the analytical phase and 3) the post-analytical phase. [3] The pre-analytical phase is related to sample collection, transport, accession and processing. The analytical phase is related to actually carrying out the test (manual/automated) and the activities that follow (transmission of results, storage/disposal of samples, maintenance of test data, etc.) comprise the post-analytical part. In the departments such as clinical biochemistry, hematology and immunoassay where numerical data is obtained, methods for analysis of quality are well established. When descriptive reports are made, such an assessment becomes less simple though not unachievable. The following is an overview of all the processes involved in the generation of a quality histopathology report. The author's experiences in convening a small scale EQA program are also described.

From quality control to total quality management

The terms Quality Control (QC), Quality Assurance (QA) and Total Quality Management (TQM) are defined in more ways than one. They differ from each other in the degree of process and organizational involvement, which is overall and maximal in TQM. For all practical purposes, all these elements should be focused to a) generate an accurate histopathology report and b) enable easy retrieval and review if needed over a defined time period.

A good quality histological section is the starting point of an accurate histopathology report. All the processes involved in generating the section may be grouped under the pre-analytical part. The analytical part concerns the interpretation of the slide and making an accurate diagnosis. The post-analytical part involves the generation and transmission of the histopathology report, storage/disposal of samples, slides and blocks and proper retention of test results. [Table 1] adequately describes the processes involved in each part. These will be individually discussed.

Pre-analytical aspects

All processes involved up to the submission of stained slides for analysis are grouped under pre-analytical. Newer models for the pre-analytical phase also include aspects like patient satisfaction with the collection process, professional staff satisfaction with arrangements made by the laboratory towards sample collection and transport, etc. [4]

Various studies indicate that the majority of errors in the laboratory relate to the pre-analytical phase. [5] The same can be said of the histopathology laboratory as well. [6] A lot has been said and written about the importance of primary fixation and the choice of fixatives for specific histopathology investigations. At this juncture, it is worth reiterating that the responsibility to ensure that documented instructions containing relevant information are made available at all points of specimen collection rests with the laboratory. Correct patient identification by a unique accession number that is traceable to the specimen and report all through the process is of prime importance. Errors in this area are common but avoidable. The author has found immense benefit in using Bar Code technology to minimize errors in sample accession and identification. Similarly, wrong identification of anatomic location as well as laterality of biopsy (right/left) are common errors that should be avoided. It would be worth while for the laboratory to design its own "referral form" for histopathology and immunohistochemistry and make it available to all areas of sample collection. This form should provide space for entry of the relevant clinical data. It may be useful to insert check boxes for better clinician compliance. Dialogue with the clinician about the importance of properly filled forms may be needed. Whenever clinical data is not provided, the laboratory should take the initiative to extract relevant data either from the treating physician or hospital files. Other areas of error in the pre-analytical phase include lost specimens, inadequate volume, size, gross description, gross sampling, erroneous measurements, extraneous tissue (floaters), [7] improper sections/inadequate serials, poor staining and mounting quality, etc.

Listed below are few of the steps one may implement to achieve proper control of the pre-analytical process.

  1. Standard procedures for sample accession, identification, acceptance/rejection, gross examination and sampling and all the steps that follow must be documented. This standard operating procedure (SOP) should be written in simple language that can be understood by all. The SOP should be available at the workplace and all technical staff should be aware of its contents.
  2. Planned changing of chemicals used for processing based on the number of tissues passed through. This schedule will prevent under processing and unnecessary rework and loss of tissue. The laboratory should record the number of tissues passed through every day and compulsorily change the chemicals once the pre-determined limit is reached. The limit may be set based on the laboratory's experience. The same also applies to the deparaffinization, staining, dehydration and clearing steps for sections.
  3. Usage of controls for routine and special stains daily as a routine is strongly recomended. For routine H & E staining, the laboratory may identify one tissue block with a good mixture of hematoxyphilic and eosinophilic tissue (cervix, fibroadenoma, etc.) as a control. Multiple slides may be cut and kept aside to be used as controls. The control slide should be stained before the routine batch of slides and the staining character should be compared with that of the previous day. By putting aside one block for control, one avoids variation related to tissue type. Similarly, known controls (positive and negative) should be used for histochemical staining. A record of the staining character should be maintained. The paraffin used for impregnation and embedding should be of good quality with an appropriate melting point.
  4. Recording the temperature of the paraffin bath, water floatation bath and slide warming table should be done on a daily basis. These and other equipment should be of standard quality and calibrated at periodic intervals.
  5. The microtome should be of good quality and serviced regularly. Periodic calibration of the micrometer should be made to ensure consistency of section thickness. The importance of proper maintenance of the knife need not be reiterated. The use of disposable blades is recommended.
  6. Care should be taken not to induce tissue artifacts due to improper processing, sectioning, staining and mounting.
  7. Last but not the least, the label affixed on the stained slide should be of an appropriate size so that it does not project beyond the slide or cover the tissue sections. The identification should be legible and should ideally carry the name of the laboratory. Using bar code labels, one can incorporate demographic data such as the name of the laboratory, the name of the patient, the laboratory ID number and the date.

Post-analytical aspects

The traditional laboratory approach to the post-analytical phase involves report generation without transcription errors, report transmission/dispatch to the right person(s), storage of reported material as well as reported data and safe disposal of specimens thereafter. Newer models include billing issues, patient safety issues (reporting of critical results), turn around time (TAT) and general customer satisfaction (wait times), [4] etc. Monitoring of TAT is of vital importance and laboratories should strive to achieve the goal of signing out the majority of cases within 48 hours of receipt of the specimen. The use of microwaves may assist in improving the TAT especially for small biopsies. The TAT of frozen sections should also be monitored and potential bottle-necks should be eliminated. The retention period for specimens has always been a subject of debate and national guidelines for this are warranted.

Analytic aspects

Unlike in other disciplines of laboratory medicine, assessment of analytical aspects in histopathology is not easy given the subjectivity of the reports. Error detection and avoidance in histopathology has been written about very often. [8],[9],[10],[11],[12] Various modes of internal audits have been described and recommended, [13] each with their advantages. The following general recommendations are being made at this stage.

1. For departments with more than one pathologist:

  • Intra-departmental consultation (review of selected cases by colleagues)

  • Comparison with other reports (frozen/cytology/histopathology)

  • Random case review (blinded re-reporting of random cases)

    1. By the same person (check for precision)
    2. By a different person (check for accuracy)

  • Hierarchical form of reporting

  • Intra- and inter-departmental conferences (clinico-pathological conference (CPC)/clinical rounds)

2. For laboratories run by single pathologist: Many laboratories in India are run by single pathologists who do all the reporting. Though this is a disadvantageous situation, reasonable quality may still be achieved by implementing the following:

  • Random blinded review of reported cases (precision check)
  • External consultations (may need to be done more often)
  • Review by experts
  • Participation in continued medical education (CME) programs

External quality assessment (Proficiency testing)

Accrediting authorities insist that every laboratory should have some form of external quality assessment for all the tests performed under its scope of activity. [14] Organized EQA programs are available in other countries (CAP, UK-NEQAS). These are either prohibitively expensive or not easily available in India. The Indian College of Pathology in collaboration with the Association of Pathologists of North America (AIPNA) has initiated a program. There is a need to organize and participate in a structured EQA program on a regional and national scale. The author has had personal experience in coordinating a program that has catered to NABL accredited laboratories for 3 years. The structure of this program is detailed along with pertinent data from participating laboratories.

The Inter-Laboratory Quality Assessment program for Histopathology (ILQA-HP) was launched in the year 2006 as part of the activities of parent organization ILQA-Bangalore. The program was started with the immediate objective of providing external quality assessment in histopathology to NABL accredited laboratories in India, with the long-term goal of including non accredited laboratories into the program. The scheme is divided into two portions: the first assessing the pre-analytical aspects and the second assessing the analytical aspects.

Part 1: Pre-analytical aspects

Slices of formalin fixed tissue measuring approximately 1x1x0.5 cms are made from one common source and mailed to each of the participating laboratories who in turn process the tissue, make stained sections and return the slides to the nodal laboratory for pre-analytical assessment. Attempts are made to cover a wide spectrum of tissues ranging from skin, adipose tissue, thyroid, fibrotic/hyalinized tissue, bone, etc. The stained sections are scored by an independent expert as follows: Score 1 = unsatisfactory, 2 = poor, 3 = average, 4 = good and 5 = excellent. A total of 15 marks are allotted under the following headings:

  1. Processing - 5 marks
  2. Sectioning - 5 marks
  3. Staining - 5 marks

Laboratories that score less than 3 in any of the areas are advised to take immediate corrective actions. The progress of laboratories over time is summarized in [Table 2]. Only laboratories that have completed at least four cycles have been included in the analysis. Analysis of mean scores of all participating laboratories for sections of uterus has improved from 8.73 in Cycle 1 of 2006 to 10.3 in Cycle 4 of 2007 (11 laboratories). The average score for 23 laboratories for skin sections was 11.06 in Cycle 1 of 2007 and 11.2 in Cycle 2 of 2008. The average scores were found to be lower when tissues like thyroid (9.25), bone (10.4) and adipose tissue (10.8) were distributed. There has been a positive trend in performance of individual laboratories provided the "difficult tissues" have been taken into consideration.

Part 2: Analytical aspects

The general recommendations as defined by the Royal College of Pathologists [15] were adopted. Sections obtained from one common tissue block were stained with Hematoxylin and Eosin and distributed to all participating laboratories along with relevant clinical history and other information. The following were ensured:

  1. The cases were in tune with the routine practice of any laboratory. Special cases were avoided.
  2. The cases did not fit into "seminar cases" or "pathology curiosities" and were related to the common slides encountered in routine practice.
  3. The cases were not all straight forward.
  4. The cases did not rely too heavily/solely on immunohistochemistry for a diagnosis. In such an event, the details of immune reaction (along with a picture) would be given.

All the diagnoses received within the notified period were analyzed and a consensus diagnosis was given (it is presumed that the consensus diagnosis is the accurate one) being well aware of the limitations of this approach. [Table 3] details the cases that constitute Part 2 of the program. Analysis of the data in [Table 3] has given a few interesting conclusions:

  1. There is a lack of consensus in classification of lymphomas
  2. Gleason scoring of prostatic adenocarcinoma needs further uniformity
  3. The major area of discordance lies in the identification and quantification of mitotic activity. This has been noted in three situations (mitotically active phylloides tumor, vascular right atrial tumor with increased mitoses and uterine smooth muscle tumor with coagulative necrosis)

This Interlaboratory QA program has been a beginning and has scope for improvement on many fronts including the introduction of a score based evaluation of concordance/discordance. The numbers are still not large enough to draw definitive statistical information.

Recommendations for a National QA program

The author makes the following recommendations:

  1. Establishment of zonal/nodal centers that would conduct/coordinate similar activities in their respective regions. These centers may operate on a self-sustainable basis through nominal subscription fees
  2. Establishment of a program that would periodically evaluate the nodal centers
  3. Establishment of a central coordinating body (Indian College of Pathologists/IAPM/NABL/QCI) that would monitor activities and support the nodal centers with operational and financial resources
  4. Affiliation of the national coordinating body with similar organizations with related activities worldwide

   Acknowledgements Top

The author acknowledges the Inter-Laboratory Quality Assessment Scheme (Histopathology) (ILQA-HP) of Bangalore, of which the author is the co-convener and program coordinator.

   References Top

1.Kohn L, Corrigan J, Donaldson M. editors. To err is human: Building a safer health system. Washington DC: National Academics Press; 2000.  Back to cited text no. 1    
2.National Patient Safety Goals. Joint Commission on Accreditation of Healthcare Organization. Available from: [cited in 2004].  Back to cited text no. 2    
3.Barr JT. Clinical laboratory utilization: Rationale. In: Davis B, Mass D, Bishop M, editors. Principles of clinical laboratory utilization and consultation. Philadelphia, PA: Saunders; 1999. p. 6.  Back to cited text no. 3    
4.Hollensead SC, Lockwood WB, Elin RJ. Errors in pathology and laboratory medicine: Consequences and prevention. J Surg Oncol 2004;88:161-81.  Back to cited text no. 4  [PUBMED]  [FULLTEXT]
5.Wiwanitkit V. Types and frequency of pre-analytical mistakes in the first Thai ISO 9002:1994 certified clinical laboratory: A 6 month monitoring. BMC Clin Pathol 2001;1:1-5.  Back to cited text no. 5    
6.Sharif MQ, Mushtaq S, Mamoon N, Jamal S, Luqman M. Clinician's responsibility in pre-analytical quality assurance of histopathology. Pak J Med Sci 2007;23:720-3.  Back to cited text no. 6    
7.Zarbo RJ, Meier FA, Raab SS. Error detection in anatomic pathology. Arch Pathol Lab Med 2005;129:1237-45.  Back to cited text no. 7  [PUBMED]  [FULLTEXT]
8.Owen DA, Tighe JR. Quality evaluation in histopathology. Br Med J 1975;1:149-50.  Back to cited text no. 8  [PUBMED]  [FULLTEXT]
9.Zuk JA, Kenyon WE, Myskow MW. Audit in histopathology: Description of an internal quality assessment scheme with analysis of preliminary results. J Clin Pathol 1991;44:10-6.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]
10.Hocking GR, Niteckis VN, Cairns BJ, Hayman JA. Departmental audit in surgical anatomical pathology. Pathology 1997;29:418-21.  Back to cited text no. 10  [PUBMED]  
11.Lesna M. Assessing diagnostic errors: When is suspension of a pathologist justified? J Clin Pathol 1998;51:649-51.  Back to cited text no. 11  [PUBMED]  [FULLTEXT]
12.Ramsay AD. Errors in histopathology reporting: Detection and avoidance, A review. Histopathology 1999;34:481-90.  Back to cited text no. 12  [PUBMED]  [FULLTEXT]
13.Association of Directors of Anatomic, Surgical Pathology, recommendations on quality control and quality assurance in anatomic pathology. Am J Surg Pathol 1991;15:1007-9.  Back to cited text no. 13    
14.Assuring quality of examination procedures. Clause 5.6. In International Standard IS/ISO 15189. Medical Laboratories - Particular requirements for quality and competence. 2nd ed. ISO; 2007. p. 22-3.  Back to cited text no. 14    
15.Royal College of Pathologists. Recommendations for the development of Histopathology and Cytopathology External Quality Assurance Systems - RCP 1998.  Back to cited text no. 15    

Correspondence Address:
Jayaram N Iyengar
Anand Diagnostic Laboratory, No. 11, Blue Cross Chambers, Infantry Road Cross, Bangalore - 560 001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.44951

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