Overview
Hematocrit (packed cell volume) is the proportion of whole blood occupied by red cells, reported as a fraction (L/L) or percentage.
Clinical Importance
To assess red-cell mass in parallel with hemoglobin
To support evaluation of anemia, polycythemia, and hemoconcentration
Specimen Requirements
- Specimen: whole blood
- Tube: lavender-top K₂EDTA (preferred) or K₃EDTA
- Anticoagulant: EDTA
- Handling: invert gently 8–10 times immediately after draw; do not shake
- Storage: room temperature preferred for prompt analysis; follow analyzer/manufacturer limits
- Stability: analyze as soon as practical (many CBC parameters are stable for several hours at room temperature; verify local procedure). MPV increases with EDTA storage time. Do not freeze whole blood for CBC.
Analytical Method
Manual microhematocrit: centrifugation packs RBCs; packed column height ÷ total column = volume fraction (CLSI H07).
Automated CBC: Hct is commonly derived as RBC (× 10¹²/L) × MCV (fL) with instrument-specific scaling, so calculated Hct inherits RBC and MCV error.
Instruments Used
Automated analyzers
- Sysmex XN / XN-L series hematology analyzers
- Beckman Coulter DxH series hematology analyzers
- Abbott Alinity hq / CELL-DYN hematology analyzers
- Siemens Healthineers ADVIA hematology analyzers
- Mindray BC-series hematology analyzers
- HORIBA Yumizen / ABX hematology analyzers
Manual methods
- Microhematocrit centrifugation (CLSI H07 method context)
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Typical published adult intervals: men 0.40–0.50 L/L (40–50%); women 0.36–0.46 L/L (36–46%).
Altitude and pregnancy alter expected intervals.
Interpretation
Critical and significant-risk limits are institution-defined (CLSI GP47). Confirm the local call list. Textbook examples are not universal thresholds.
Critical values
- Extreme Hct values may be included on institutional critical lists with Hb; verify locally
Common Causes of Increased Results
- Elevated Hct with elevated Hb/RBC suggests polycythemia or hemoconcentration
Common Causes of Decreased Results
- Decreased Hct parallels anemia when plasma volume is stable
Clinical Significance
- Anemia and polycythemia assessment with hemoglobin
- Monitoring plasma volume shifts and dialysis/critically ill patients where ordered
Factors Affecting Results
Pre-analytical
- Clotted specimen, underfilled tube, or improper mixing
- Prolonged tourniquet time or difficult draw causing hemoconcentration
- IV fluid contamination or drawing above an infusion site
- Excessive delay before analysis (cell swelling, platelet clumping risk)
Analytical
- Analyzer flag for interference (lipemia, hemolysis, cold agglutinins, extreme leukocytosis)
- Calibration or QC failure
- Fragmented RBCs or giant platelets misclassified depending on channel
Post-analytical
- Wrong demographic reference interval applied
- Failure to review delta checks or instrument flags before release
- Unit confusion (g/L vs g/dL for hemoglobin)
Advantages and Limitations
Advantages
- Intuitive volume-fraction measure of red-cell mass
- Manual microhematocrit available as backup
Limitations
- Calculated automated Hct is not independent of RBC and MCV errors
- Trapped plasma in microhematocrit can slightly overestimate PCV
Clinical Pearls
If automated Hct and hemoglobin disagree markedly (rule-of-three mismatch), investigate cold agglutinins, lipemia, or instrument flags before release.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details 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.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Validation, Verification, and Quality Assurance of Automated Hematology Analyzers; Approved Standard. CLSI document H26-A2. CLSI; 2010.
- 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.
- Clinical and Laboratory Standards Institute. Procedure for Determining Packed Cell Volume by the Microhematocrit Method; Approved Standard. CLSI document H07-A3. CLSI; 2000.
Frequently Asked Questions
Common questions about using this Hematocrit (Hct) laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Hematocrit (Hct) laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Hematocrit (Hct). Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Hematocrit (Hct) specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Hematocrit (Hct). Confirm collection details against your laboratory protocol.
Where are Hematocrit (Hct) reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Hematocrit (Hct) results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Hematocrit (Hct)?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Hematocrit (Hct)?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Hematocrit (Hct)?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for Hematocrit (Hct)?
See the Clinical Pearls section for concise laboratory practice notes associated with Hematocrit (Hct). Apply pearls alongside institutional protocols.
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