This manuscript is intended to provide a best practice approach to accurately and consistently assess toxicant-induced bone marrow effects of test articles. In nonclinical toxicity studies, complete blood count data in conjunction with the histological examination of the bone marrow are recommended as the foundation for assessing the effect of test articles on the hematopoietic system. This approach alone can be used successfully in many studies. However, in some situations it may be necessary to further characterize effects on the different hematopoietic lineages, either by cytological or flow cytometric evaluation of the bone marrow. Both modalities can be used successfully, and which one is selected will depend on the expertise, preference of the facility, and the nature of the change in the bone marrow. Other specialized techniques such as clonogenic assays or electron microscopy are used rarely to further characterize hematotoxicity. The indications and techniques to successfully employ histological, cytological, or flow cytometric evaluation as well as clonogenic assays and electron microscopy are reviewed.

The purpose of this paper by the Regulatory Affairs Committee (RAC) of the American Society for Veterinary Clinical Pathology (ASVCP) is to review the current regulatory guidances (eg, guidelines) and published recommendations for best practices in veterinary toxicologic clinical pathology, particularly in the pharmaceutical and biotechnology industries, and to utilize the combined experience of ASVCP RAC to provide updated recommendations. Discussion points include (1) instrumentation, validation, and sample collection, (2) routine laboratory variables, (3) cytologic laboratory variables, (4) data interpretation and reporting (including peer review, reference intervals and statistics), and (5) roles and responsibilities of clinical pathologists and laboratory personnel. Revision and improvement of current practices should be in alignment with evolving regulatory guidance documents, new technology, and expanding understanding and utility of clinical pathology. These recommendations provide a contemporary guide for the refinement of veterinary toxicologic clinical pathology best practices.

This manuscript is intended to provide a best practice approach to accurately and consistently assess toxicant-induced bone marrow effects of test articles. In nonclinical toxicity studies, complete blood count data in conjunction with the histological examination of the bone marrow are recommended as the foundation for assessing the effect of test articles on the hematopoietic system. This approach alone can be used successfully in many studies. However, in some situations it may be necessary to further characterize effects on the different hematopoietic lineages, either by cytological or flow cytometric evaluation of the bone marrow. Both modalities can be used successfully, and which one is selected will depend on the expertise, preference of the facility, and the nature of the change in the bone marrow. Other specialized techniques such as clonogenic assays or electron microscopy are used rarely to further characterize hematotoxicity. The indications and techniques to successfully employ histological, cytological, or flow cytometric evaluation as well as clonogenic assays and electron microscopy are reviewed.

In preclinical safety assessment, blood volume requirements for various endpoints pose a major challenge. The goal of this working group was to review current practices for clinical pathology (CP) testing in preclinical toxicologic studies, and to discuss advantages and disadvantages of methods for reducing blood volume requirements. An industry-wide survey was conducted to gather information on CP instrumentation and blood collection practices for hematology, clinical biochemistry, and coagulation evaluation in laboratory animals involved in preclinical studies. Based on the survey results and collective experience of the authors, the working group proposes the following "points to consider" for CP testing: (1) For most commercial analyzers, 0.5 mL and 0.8 mL of whole blood are sufficient for hematology and biochemistry evaluation, respectively. (2) Small analyzers with low volume requirements and low throughput have limited utility in preclinical studies. (3) Sample pooling or dilution is inappropriate for many CP methods. (4) Appropriate collection sites should be determined based on blood volume requirements and technical expertise. (5) Microsampling does not provide sufficient volume given current analyzer and quality assurance requirements. (6) Study design considerations include: the use of older/larger animals (rodents), collection of CP samples before toxicokinetic samples, use of separate subsets of mice for hematology and clinical biochemistry testing, use of a priority list for clinical biochemistry, and when possible, eliminating coagulation testing.

Bronchoalveolar lavage (BAL) is a simple procedure that is used to investigate drug efficacy or lung toxicity. It is sensitive to lung changes and less invasive than histological evaluation. It can be performed repeatedly at interim time points or as a terminal procedure. Airborne contaminants and purposely inhaled compounds, resident and inflammatory cells, as well as different cellular soluble products can be harvested in bronchoalveolar fluid (BALF) and measured. Bronchoalveolar lavage can also be an important tool to understand drug exposure and its metabolism in the lung, although it should be rigorously performed and interpreted with caution, especially in the context of regulated toxicology studies. This review focuses on the methods and uses of BAL in animal research, primarily in the pharmaceutical industry, as well as for the assessment of drugs, pollutants, and chemical lung toxicity. Methods of collecting and analyzing BALF and parameters affecting variability are discussed in detail. Improved automated methods for cell counting and analysis of the inflammatory cellular differential using hematology analyzers, common markers of lung injury, and new methodologies are described. Correlation between BALF and histological evaluation should not be considered as repetitive but as complementary assessments in the context of efficacy and toxicity studies.