Introduction
Haematocrit, also known as Packed Cell Volume, represents one of the most essential parameters in hematology for evaluating red cell mass. PCV Estimation determines the percentage of packed red blood cells present in a given volume of whole blood and helps clinicians assess oxygen-carrying capacity. Because red blood cells play a vital role in tissue oxygenation, even minor changes in haematocrit values carry strong clinical significance. Laboratory professionals frequently rely on this test for anemia screening, hydration assessment, and calculation of red cell indices.The term “haematocrit” literally refers to the separation of blood components under centrifugal force. During testing, red cells settle at the bottom, plasma remains at the top, and a thin buffy coat forms in between. This separation allows accurate measurement of red cell volume in relation to total blood volume.
Clinical Importance of PCV
Clinicians use PCV values to:
Screen and classify anemia
Detect polycythemia
Assess dehydration status
Calculate MCV and MCHC
Monitor chronic disease progression
In addition, laboratories use the Wintrobe tube to perform both PCV and ESR using the same specimen, which improves efficiency in routine hematology work.
Methods of Measurement of PCV
Laboratories determine haematocrit using three primary approaches. Each method suits specific clinical and technical settings.
1. Direct Method
(a) Macro-Method — Wintrobe Tube Method
This classical approach uses a Wintrobe haematocrit tube and remains popular in teaching laboratories.
(b) Micro-Method — Capillary Tube Method
This technique requires only a small blood volume and proves ideal for pediatric and bedside testing.
2. Electronic Method
Automated hematology analyzers calculate haematocrit indirectly by multiplying RBC count with MCV. Modern analyzers generate results within seconds along with complete blood count parameters.
Wintrobe’s Method
The Wintrobe method forms the foundation of traditional PCV Estimation and provides reliable results when performed carefully.
Identification of Wintrobe Haematocrit Tube
The Wintrobe tube has unique structural features:
Thick-walled glass construction
Length of 11 cm
Internal diameter of 2.5 mm
Flat inner base
Graduations at 1 mm intervals up to 100 mm
Dual markings: ascending scale for PCV and descending scale for ESR
The tube holds approximately 1 ml of blood and allows clear visualization of blood layers after centrifugation.
Uses of Wintrobe Tube
Laboratories use the Wintrobe tube for multiple purposes:
Determination of PCV
Measurement of ESR
Buffy coat smear preparation
Study of abnormal blast cells
LE cell preparation in autoimmune disorders
Anticoagulant Used
Venous blood collection requires anticoagulation to prevent clot formation. Double oxalate or heparin serves as the anticoagulant of choice for Wintrobe testing. Correct anticoagulant concentration ensures accurate cell packing and prevents dilution errors.
Method (Wintrobe Technique)
The laboratory professional follows a structured sequence:
Collect 2 ml of venous blood using appropriate anticoagulant
Mix the sample gently to ensure uniform cell distribution
Fill the Wintrobe tube from bottom to zero mark using a long Pasteur pipette
Place the tube in a centrifuge
Spin at 3000 rpm for 30 minutes with a radius of 15 cm
Read the packed red cell column using the ascending scale
The result appears as a percentage of total blood volume.
ESR Determination Using Wintrobe Tube
For ESR measurement, the same tube stands vertically on a rack for one hour. The descending scale indicates plasma fall, allowing ESR calculation without additional equipment.
Zones Seen After Centrifugation
After centrifugation, three distinct layers appear clearly.
1. Packed Red Cells (PCV Layer)
This bottom layer consists of erythrocytes. Normal values range from 45–50% in adults.
2. Buffy Coat
This thin grayish layer contains leukocytes and platelets. Normal thickness remains around 2–3%.
Uses of Buffy Coat Smear:
Diagnosis of SLE through LE cell detection
Evaluation of subleukemic leukemia
Cytochemical study of blast cells
3. Plasma
The upper layer contains plasma and appears clear to pale yellow. Normal plasma volume ranges from 48–52%.
Special Observation:
Yellow, green, or orange plasma suggests jaundice, while an expanded buffy coat indicates leukocytosis or leukemia.
Normal Range of PCV
| Group | Normal Range |
|---|---|
| Adult Men | 40–54% |
| Adult Women | 36–47% |
| At Birth | 44–62% |
| At 1 Year | ~35% |
| At 10 Years | ~37.5% |
Abnormal PCV Values
Diminished PCV
PCV values below 30% commonly indicate anemia due to iron deficiency, chronic disease, or blood loss.
Increased PCV
Elevated values occur in:
Polycythemia
Severe dehydration
Cholera
Acute gastroenteritis
These conditions increase blood viscosity and oxygen-carrying capacity artificially.
Sources of Error in Wintrobe Method
Several technical factors affect accuracy:
Improper blood mixing
Inadequate centrifugation speed or time
Irregular tube bore
Trapped leukocyte-platelet clumps
Excess anticoagulant
Strict technique minimizes these errors.
Microhaematocrit Method (Capillary Tube Method)
The microhaematocrit technique provides a faster and more convenient approach to PCV Estimation, especially in routine laboratory settings.
Introduction
This method uses a capillary tube measuring 75 mm in length and approximately 1 mm in diameter.
Procedure
Fill the capillary tube up to three-fourths with blood
Seal one end using wax, putty, or microburner
Place the tube in a microhaematocrit centrifuge
Centrifuge for 5 minutes with sealed end outward
Measure PCV using a millimeter scale
Normal Range (Micro-Method)
Male: 47 ± 7%
Female: 43 ± 5%
Advantages
Requires minimal blood volume
Suitable for finger-prick samples
Short centrifugation time
Ideal for pediatric patients
Precautions
Record readings promptly
Avoid including buffy coat
Prevent finger squeezing during sample collection
Sources of Error
Prolonged tourniquet application
Excess EDTA concentration
Muscular activity before sampling
Electronic Method
Automated analyzers calculate PCV Estimation indirectly using RBC count and MCV. These systems deliver rapid, reproducible, and highly accurate results, making them standard in modern laboratories.
LE Cell Test
Autoimmune diseases involve antibodies against nuclear components. The LE cell test detects antinuclear antibodies, especially in systemic lupus erythematosus.
LE factor represents an IgG antibody directed against deoxyribonucleoprotein.
Principle of LE Cell Formation
Glass bead agitation damages neutrophil nuclei and exposes nucleoproteins. LE factor reacts with this material, forming homogeneous LE bodies. Neutrophils then phagocytose these bodies, producing characteristic LE cells.
LE Cell Preparation Method
Collect 6 ml of blood in a plain tube
Incubate at 37°C for 1 hour
Separate serum for other tests
Grind clot through mesh
Incubate residue again
Fill Wintrobe tubes and centrifuge
Prepare buffy coat smears
Fix with methanol and stain with Giemsa
Result Interpretation
Positive samples show LE cells and free LE bodies. Laboratory professionals must differentiate LE cells from tart cells, which retain chromatin structure and lack diagnostic significance.
Diseases Showing LE Cells
Systemic lupus erythematosus
Lupoid hepatitis
Rheumatoid arthritis
Penicillin sensitivity
Other collagen vascular disorders
Glass Bead Method
This advanced technique improves defibrination and nuclear damage.
Procedure
Add glass beads to heparinized blood
Shake vigorously
Incubate at 37°C
Centrifuge
Prepare buffy coat smears
Morphology of LE Cell
An LE cell shows:
Neutrophil with large basophilic inclusion
Displaced nucleus
Rosette formation in early stages
Importance of PCV in Clinical Practice
Accurate PCV Estimation guides diagnosis, monitors disease severity, and supports therapeutic decisions. Combined with hemoglobin and RBC indices, haematocrit provides a complete picture of red cell status.
Conclusion
PCV Estimation remains a cornerstone investigation in hematology. Wintrobe, microhaematocrit, and electronic methods each serve specific roles depending on laboratory infrastructure. Mastery of technique, awareness of errors, and correct interpretation ensure reliable results and strong clinical correlation.
Disclaimer
This article provides educational information for laboratory science and medical learning purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always follow institutional protocols and consult qualified healthcare professionals.
Frequently Asked Questions
1. Why is PCV important in anemia diagnosis?
It reflects red cell mass and helps classify anemia severity.
2. Which method gives fastest PCV results?
Automated analyzers provide results within seconds.
3. Can PCV and ESR be done using the same tube?
Yes, the Wintrobe tube allows both measurements.
Written by Jambir Sk Certified Medical Laboratory Technologist
Disclaimer: This content is for educational purposes only and should not be consideredas medical advice. Always consult a qualified doctor.We do not provide professional medical advice, diagnosis, or treatment.All health-related content is based on research, knowledge, and general awareness.Always consult a licensed healthcare provider for any medical concerns.HealthSeba.com will not be responsible for any loss, harm, or damage caused by the use of information available on this site.
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