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ESR and PCV Physiology

1. ESR: Erythrocyte Sedimentation Rate

Definition:
ESR is the distance that red blood cells (RBCs) fall in a vertical column of anticoagulated blood in 1 hour. It is expressed in mm/hour.

It is a nonspecific marker of inflammation. It does not diagnose a particular disease by itself.

Principle of ESR

Normally, RBCs carry a negative surface charge called zeta potential. This causes the cells to repel each other and remain dispersed in plasma.

During inflammation, plasma concentrations of acute-phase proteins, especially fibrinogen, increase.

Fibrinogen reduces the repulsion between RBCs.
RBCs stick together in stacks called rouleaux.
Rouleaux are heavier and settle more rapidly.
Therefore, the ESR rises.

Key line:

Increased plasma fibrinogen -> rouleaux formation -> faster sedimentation -> raised ESR.

The ESR occurs in three stages:

Stage	Approximate time	What happens
Aggregation phase	First 10 min	RBCs form rouleaux, little settling occurs
Sedimentation phase	Next 40 min	RBCs settle at a fairly constant rate
Packing phase	Last 10 min	RBCs accumulate at bottom, settling slows

Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 562.

ESR methods

Westergren method: Standard and commonly used method. Uses a 200 mm vertical tube.
Wintrobe method: Uses a shorter tube and can also be used for PCV.

Typical reference ranges

Ranges differ among laboratories and rise with age. Common approximate adult values are:

Male: 0-15 mm in first hour
Female: 0-20 mm in first hour

Causes of increased ESR

Physiological

Female sex
Increasing age
Pregnancy
Menstruation

Pathological

Acute and chronic infections, especially tuberculosis
Inflammatory and autoimmune disorders, such as rheumatoid arthritis
Tissue injury or necrosis
Malignancy
Chronic kidney disease
Anemia
Multiple myeloma and other conditions with increased immunoglobulins

Causes of decreased ESR

Polycythemia or increased RBC count
Sickle-cell disease and marked poikilocytosis, because abnormal-shaped RBCs do not form rouleaux well
Severe leukocytosis
Low fibrinogen level, for example in hypofibrinogenemia

Factors influencing ESR

Factor	Effect on ESR	Reason
Fibrinogen and globulins increase	Increases	Promotes rouleaux
Albumin increase	Decreases	Retards sedimentation
Anemia / low PCV	Increases	More plasma relative to RBCs, easier settling
Polycythemia / high PCV	Decreases	More RBC crowding, slower settling
Macrocytes	Increases	Larger cells settle faster
Microcytes	Decreases	Smaller cells settle slowly
High temperature	Increases	Faster sedimentation
Tilted ESR tube	Falsely increases	Alters settling path

ESR must always be interpreted along with history, examination, and tests such as CRP. It may remain elevated longer than CRP after inflammation improves. The MedlinePlus ESR overview also emphasizes that it is a nonspecific inflammation test.

2. PCV: Packed Cell Volume

Other names: Hematocrit, HCT.

Definition:
PCV is the percentage of total blood volume occupied by packed red blood cells after centrifuging anticoagulated blood.

[ \text{PCV (%)} = \frac{\text{Height of packed red-cell column}}{\text{Total height of blood column}} \times 100 ]

Principle

When anticoagulated blood is centrifuged, its components separate according to density:

Bottom: Packed RBCs, the heaviest component
Middle: Buffy coat, made of WBCs and platelets
Top: Plasma

PCV measures the RBC layer as a percentage of the whole blood column.

Centrifuged blood showing plasma, buffy coat and erythrocyte layers

Methods of measuring PCV

Microhematocrit method
- Blood is filled in a heparinized capillary tube.
- One end is sealed.
- It is centrifuged at high speed.
- PCV is read using a hematocrit reader.
- Commonly used in practical physiology.
Wintrobe method
- Blood is placed in a Wintrobe tube and centrifuged.
- The same tube can help determine ESR and PCV.
Automated analyzer
- Modern laboratories commonly calculate hematocrit from RBC count and MCV.

[ \text{Hematocrit (%)} \approx \frac{\text{RBC count} \times \text{MCV}}{10} ]

Normal PCV values

Approximate adult ranges:

Group	PCV
Adult male	40-50%
Adult female	36-45%
Newborn	50-60%

In normal blood, RBCs occupy roughly 45% of blood volume, plasma about 55%, and the buffy coat less than 1%. Histology: A Text and Atlas with Correlated Cell and Molecular Biology, p. 668.

Increased PCV

This occurs due to either a real increase in RBC mass or loss of plasma.

Polycythemia vera
High altitude
Chronic hypoxia, for example chronic lung disease or cyanotic heart disease
Dehydration, vomiting, diarrhea, burns

Decreased PCV

Anemia
Acute or chronic blood loss
Hemolysis
Nutritional deficiencies, such as iron, vitamin B12, or folate deficiency
Pregnancy, due to increased plasma volume
Bone marrow failure

Clinical importance of PCV

PCV gives an estimate of:

Red cell mass
Oxygen-carrying capacity, together with hemoglobin
Severity of anemia
Hemoconcentration or dehydration
Polycythemia

Relationship between ESR and PCV

This is a frequently asked MBBS viva point:

Low PCV, as in anemia -> ESR increases.
High PCV, as in polycythemia -> ESR decreases.

Reason: in anemia, the lower RBC concentration favors rouleaux formation and settling. In polycythemia, abundant RBCs hinder free settling.

One-line viva answers

ESR: Rate at which RBCs settle in a column of anticoagulated blood in one hour.
Unit of ESR: mm in the first hour.
PCV: Percentage of blood volume occupied by packed RBCs after centrifugation.
Other name for PCV: Hematocrit.
Why does ESR rise in inflammation? Increased fibrinogen causes rouleaux formation, so RBCs settle faster.
Why does ESR rise in anemia? Reduced RBC concentration favors rouleaux formation and sedimentation.
Why is ESR low in polycythemia? Increased RBC concentration slows sedimentation.

Give me MBBS viva questions and answers on ESR and PCV

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MBBS Viva Questions and Answers: ESR and PCV

A. ESR: Erythrocyte Sedimentation Rate

1. What is ESR?

ESR is the rate at which red blood cells settle down in a vertical column of anticoagulated blood in one hour. It is expressed as mm in the first hour (mm/hr).

2. What is the principle of ESR?

Normally, RBCs repel each other because of their negative surface charge, called zeta potential. In inflammation, plasma fibrinogen and some globulins increase, reduce this repulsion, and promote RBC aggregation into rouleaux. These aggregates settle faster, increasing ESR.

3. What is rouleaux formation?

It is the aggregation of RBCs in coin-like stacks. It occurs more easily when fibrinogen or globulins are increased.

4. Why does fibrinogen increase ESR?

Fibrinogen decreases zeta potential between RBCs, allowing rouleaux formation. Rouleaux are heavier than individual RBCs, so they sediment more rapidly.

5. What is the unit of ESR?

Millimetres in the first hour, written as mm/hr.

6. Which anticoagulant is used for ESR?

For the Westergren method, sodium citrate is classically used. EDTA blood may also be used after appropriate dilution with citrate in many laboratories.

7. Name the methods of ESR estimation.

Westergren method
Wintrobe method
Automated ESR methods

8. Which is the standard method for ESR?

Westergren method is the standard and more sensitive method, especially for higher ESR values.

9. What is the length of the Westergren tube?

200 mm.

10. What is the length of the Wintrobe tube?

Approximately 100 mm.

11. Which method can measure both ESR and PCV?

Wintrobe tube method.

12. What are the phases of ESR?

There are three phases:

Aggregation phase: first 10 minutes, rouleaux form and little sedimentation occurs.
Sedimentation phase: next 40 minutes, RBCs settle at a nearly constant rate.
Packing phase: final 10 minutes, RBCs pack at the bottom and sedimentation slows.

Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 562.

13. What are normal ESR values?

Approximate values, which vary with age and laboratory:

Adult male: 0-15 mm/hr
Adult female: 0-20 mm/hr

14. Why is ESR normally higher in females?

Females generally have a lower hematocrit than males. A lower RBC concentration favors sedimentation. Hormonal and physiological factors may also contribute.

15. Why does ESR increase in anemia?

In anemia, the RBC concentration and PCV are reduced. The relatively larger plasma volume permits easier rouleaux formation and faster settling of RBCs.

16. Why is ESR low in polycythemia?

In polycythemia, the RBC concentration and PCV are high. The cells are crowded, which slows their settling, so ESR falls.

17. Give causes of raised ESR.

Acute and chronic infections
Tuberculosis
Autoimmune and inflammatory diseases, such as rheumatoid arthritis
Tissue injury or necrosis
Malignancy
Anemia
Pregnancy
Multiple myeloma and other paraproteinemias
Chronic kidney disease

18. Give causes of low ESR.

Polycythemia
Marked leukocytosis
Sickle-cell disease
Spherocytosis and severe poikilocytosis
Hypofibrinogenemia
Congestive heart failure

19. Why is ESR raised in multiple myeloma?

There is increased production of immunoglobulins, leading to rouleaux formation and rapid RBC sedimentation.

20. Why may ESR be low in sickle-cell anemia despite anemia?

Sickle-shaped RBCs cannot form rouleaux effectively. This reduces sedimentation and may produce a low ESR despite anemia.

21. Which plasma proteins increase ESR?

Fibrinogen is the most important. Increased globulins, especially immunoglobulins, can also raise ESR.

22. Which plasma protein decreases ESR?

Albumin tends to retard sedimentation and can lower ESR.

23. What are the technical errors that falsely raise ESR?

Tilted tube
Increased room temperature
Vibration
Delay in testing the sample
Improper anticoagulant ratio
Diluted blood sample
Dirty or wet tube

24. What are the technical errors that falsely lower ESR?

Short duration of reading
Low temperature
Improperly mixed blood
Clotted sample
Underfilling of tube
Very high hematocrit
Incorrect anticoagulant proportion

25. Is ESR a specific test?

No. ESR is a nonspecific marker of inflammation. It does not identify the cause or site of disease.

26. What is the clinical use of ESR?

It is useful for:

Supporting evidence of inflammation
Monitoring some chronic inflammatory diseases
Following disease activity in conditions such as rheumatoid arthritis, polymyalgia rheumatica, and giant-cell arteritis

27. What is the difference between ESR and CRP?

ESR	CRP
Indirect, nonspecific test	Acute-phase protein measured directly
Influenced by age, sex, anemia, RBC shape, and PCV	Less affected by RBC-related factors
Rises and falls relatively slowly	Rises and falls more rapidly
May remain elevated after recovery	Better reflects recent changes in inflammation

B. PCV: Packed Cell Volume

1. What is PCV?

Packed cell volume is the percentage of total blood volume occupied by packed red blood cells after centrifugation of anticoagulated blood.

2. What is another name for PCV?

Hematocrit, abbreviated as HCT.

3. State the formula for PCV.

[ \text{PCV (%)} = \frac{\text{Height of packed RBC column}}{\text{Total height of blood column}} \times 100 ]

4. What is the principle of PCV estimation?

On centrifugation, blood separates according to density:

Bottom: packed RBCs
Middle: buffy coat, containing WBCs and platelets
Top: plasma

The proportion occupied by packed RBCs is the PCV.

5. Which anticoagulant is used for PCV?

Heparinized capillary tube for capillary blood in the microhematocrit method
EDTA blood for venous blood samples

6. Name methods for PCV estimation.

Microhematocrit method
Wintrobe method
Automated hematology analyzer

7. Which method is commonly used in practical physiology?

Microhematocrit method, also called the capillary hematocrit method.

8. What is the normal PCV value in adult males?

Approximately 40-50%.

9. What is the normal PCV value in adult females?

Approximately 36-45%.

10. What is the normal PCV in newborns?

Approximately 50-60%.

11. What is the approximate composition of normal blood by volume?

RBCs: about 45%
Plasma: about 55%
Buffy coat: less than 1%

The buffy coat contains leukocytes and platelets. Histology: A Text and Atlas with Correlated Cell and Molecular Biology, p. 668.

12. What does low PCV indicate?

Usually anemia, blood loss, hemolysis, nutritional deficiency, bone marrow suppression, or hemodilution.

13. What does high PCV indicate?

It may indicate:

Polycythemia
Chronic hypoxia, for example at high altitude
Chronic lung disease
Cyanotic congenital heart disease
Dehydration, diarrhea, vomiting, or burns

14. Why is PCV raised in dehydration?

Plasma volume decreases due to fluid loss. RBC mass may be normal, but its proportion relative to plasma increases. This is called relative polycythemia or hemoconcentration.

15. Why is PCV reduced in pregnancy?

Plasma volume rises more than red cell mass during pregnancy, producing physiological hemodilution.

16. What is the buffy coat?

It is the thin, whitish layer between RBCs and plasma after centrifugation. It contains WBCs and platelets.

17. Why should the capillary tube be sealed before centrifugation?

To prevent leakage of blood during centrifugation.

18. Why should the sealed end of the capillary tube be placed outward in the centrifuge?

Centrifugal force packs RBCs toward the sealed outer end, preventing blood loss and allowing proper packing.

19. What are the errors in PCV estimation?

Inadequate centrifugation
Improper sealing of capillary tube
Incorrect reading on hematocrit scale
Trapped plasma between RBCs
Including the buffy coat in the RBC column
Hemolysed or clotted sample
Improper anticoagulant mixing

20. Why does trapped plasma cause an error in PCV?

A small amount of plasma remains trapped among the packed RBCs. This can cause a slight overestimation of PCV.

21. What is the relationship between hemoglobin and PCV?

A rough clinical rule is:

[ \text{Hemoglobin (g/dL)} \approx \frac{\text{PCV}}{3} ]

This is only approximate and may not hold in all anemias or abnormal RBC states.

22. How is hematocrit calculated by an automated analyzer?

It is commonly calculated from RBC count and mean corpuscular volume:

[ \text{Hematocrit (%)} \approx \frac{\text{RBC count in millions/µL} \times \text{MCV in fL}}{10} ]

23. What is the importance of PCV?

PCV helps in:

Detecting and assessing anemia
Detecting polycythemia
Assessing hemoconcentration in dehydration
Estimating red cell mass along with Hb and RBC count
Calculating red cell indices

C. Important Integrated Viva Questions

1. What happens to ESR in anemia and why?

ESR increases because reduced PCV favors rouleaux formation and allows RBCs to sediment more rapidly.

2. What happens to ESR in polycythemia and why?

ESR decreases because increased PCV and RBC crowding delay sedimentation.

3. Can ESR be high without infection?

Yes. ESR can rise in anemia, pregnancy, autoimmune diseases, malignancy, renal disease, and paraproteinemia.

4. Can a normal ESR exclude inflammation?

No. ESR is nonspecific and may remain normal in some inflammatory states. It must be interpreted with symptoms, examination, CBC, CRP, and other investigations.

5. If a patient has low PCV and high ESR, what broad possibilities should be considered?

Anemia with inflammation or chronic disease is possible. Other causes include chronic infection, autoimmune disease, malignancy, and paraproteinemia. The values alone cannot establish a diagnosis.

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