Overview
Lymphocytes are lymphoid mononuclear leukocytes mediating adaptive (B and T cells) and innate (NK) immunity. Routine automated differentials report total lymphocyte percentage without subset discrimination.
Classification
| Category | Term |
|---|---|
| Lineage | Lymphoid, mononuclear |
| Major subsets | B lymphocyte, T lymphocyte, NK cell |
| Morphologic forms | Small mature, reactive, atypical, large granular lymphocyte (LGL) |
| Related cells | Plasma cell (marrow/tissue); monocyte (myeloid, distinct) |
Morphologic Features
| Form | Nucleus | Cytoplasm | Significance |
|---|---|---|---|
| Small lymphocyte | Round; dense chromatin | Scant basophilic | Normal mature form |
| Reactive/atypical | Irregular contour | Abundant | Viral and reactive states, describe, do not overcall malignancy |
| Smudge cell | Disrupted | Remnant | Fragile lymphocytes or artifact |
Small lymphocyte
Round nucleus; scant cytoplasm.
Atypical lymphocyte
Reactive forms in viral illness.
Laboratory Characteristics
- CBC differential: LYMPH %
- ALC calculation, primary interpretive parameter
- Flags: lymphocytosis, blast/abnormal lympho
- Reflex smear for flags, atypical morphology, unexplained cytopenias
- Flow cytometry, clinician-directed for immunophenotyping
Reference Intervals
Reference intervals vary by age, laboratory, and method. Use patient-report intervals only (CLSI EP28-A3c). Pediatric lymphocyte distributions differ from adult.
Clinical and Laboratory Significance
Reactive lymphocytosis common in viral illness. Persistent unexplained lymphocytosis with monotonous small cells suggests hematology correlation, not diagnosis from CBC alone.
Differential Considerations
| Pattern | Smear | Next step framing |
|---|---|---|
| Viral reactive | Atypical lymphocytes | Clinical correlation; serial CBC |
| Persistent lymphocytosis | Monotonous small lymphocytes | Hematology workup per protocol |
| Blast flag | Blast-equivalent cells if present | Hold release; hematopathology consultation |
Comparison Tables
Compare ALC with neutrophil and monocyte absolute counts for integrated leukogram interpretation.
Classification Frameworks
WHO haematolymphoid classification applies to confirmed hematologic neoplasms, not inferred from CBC alone.
Laboratory Notes
- Subset identification requires flow cytometry, not routine differential.
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
Professional Monographs
- Barnes PW, McFadden SL, Machin SJ, Doig K. Laboratory Hematology Practice. Wiley-Blackwell; 2012.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Reference Leukocyte (WBC) Differential Count (Proportional) and Evaluation of Instrumental Methods; Approved Standard. CLSI document H20-A2. CLSI; 2007.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
WHO Publications
- World Health Organization Classification of Haematolymphoid Tumours. 5th ed. Lyon: International Agency for Research on Cancer; 2022.
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