Overview
Blood composition divides into fluid (plasma or serum after coagulation) and formed elements (erythrocytes, leukocytes, platelets). Hematology primarily enumerates and morphologically evaluates formed elements in anticoagulated whole blood.
Classification
| Compartment | Key constituents | Representative tests |
|---|---|---|
| Plasma | Water, proteins, electrolytes, gases, nutrients | Chemistry, some coagulation |
| Erythrocytes | Hemoglobin-containing cells | RBC, Hgb, Hct, indices, smear |
| Leukocytes | Granulocytes, monocytes, lymphocytes | WBC, differential, smear |
| Platelets | Megakaryocyte fragments | Platelet count, smear estimate |
Morphologic Features
Composition reference, morphology identification for individual cell lines is covered in cell-line Library entries and peripheral smear modules.
Laboratory Characteristics
- Specimen type must match test: EDTA for most CBC platforms
- Fill volume and mixing affect cell counts, pre-analytical variables
- Reported units commonly use SI (×10⁹/L, ×10¹²/L), verify LIS configuration
Reference Intervals
Reference intervals for all parameters are population- and method-specific. Establish and verify intervals per institutional protocol (CLSI EP28 framework).
| Parameter | Reporting concept | Notes |
|---|---|---|
| WBC | Absolute count per liter | Age-specific intervals common |
| Differential | Percent of 100 WBCs | Must sum to ~100% of counted cells |
| Hematocrit | Volume fraction | Correlates with RBC and MCV |
| Platelets | Absolute count per liter | Pseudothrombocytopenia from clumping, repeat per protocol |
Clinical and Laboratory Significance
Altered composition patterns (anemia, leukocytosis, thrombocytopenia) suggest which compartment is affected, disease-specific classification follows in later modules.
Differential Considerations
At composition level, distinguish specimen/type errors from true cellular abundance changes before assigning disease labels.
Comparison Tables
Plasma vs serum
| Feature | Plasma | Serum |
|---|---|---|
| Fibrinogen | Present | Absent (consumed in clot) |
| Collection | Anticoagulated tube | Clotted tube centrifuged |
| Typical use | Coagulation, some chemistry | Many chemistry panels |
Classification Frameworks
WHO haematolymphoid classifications apply to defined neoplastic entities, not to basic blood composition terminology in this reference entry.
Laboratory Notes
- Composition framing prevents misinterpretation of chemistry vs hematology results
- Absolute counts, not percentages alone, drive neutropenia and thrombocytopenia grading in practice
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. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
Frequently Asked Questions
Common questions about using this Blood Composition foundational topics Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Blood Composition laboratory reference?
Blood Composition is a Foundational Topics entry in the LabPedia Medical Laboratory Library, written for Medical Laboratory Science reference lookup.
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Can reference details vary between laboratories?
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