P2 Hematocrite, physiology


• ❖ Definition of hematocrite:

It is the percentage ratio of RBCs volume to total blood volume.

❖ Normal value: Adult male = 45%

adult female = 41 %.

❖ Measurement: Macro-Hematocrite method (wintrobe tube method):

* Materials:

1-70% alcohol

2-sterile disposable syringe

3-anticoagulant (Na citrate)

4-wintrobe tube


• * Procedure:

1- A sample of venous blood is withdrawn and prevented from clotting by

adding anticoagulant as Na citrate.

2- The blood is placed in the wintrobe tube (it is 10 cm in length and

graduated from below upwards) and centrifugated at high speed (3000

revolution / minute) for 2 about 10 minutes.

3- RBCs will be separated at the bottom leaving clear plasma above. The

hematocrite can be seen directly on its graduation.

PCV=𝐑𝐁𝐂𝐬 𝐜𝐨𝐥𝐮𝐦𝐧 𝐱 𝟏𝟎𝟎 /𝐓𝐨𝐭𝐚𝐥 𝐛𝐥𝐨𝐨𝐝 𝐜𝐨𝐥𝐮𝐦

NB 1

If plasma not clear there are two possibility:

a- haemolysis of RBCs.

b- incomplete centrifugation.

HOW to deffrentiate?

By complete centrifugation until appearance of fluffy coat

-If fluffy coat or (buffy coat) appeared & plasma turns clear this mean

and (incomplete centrifuge)

- If appear and still not clear this means ( hemolysis)

• NB 2

Other method for determination P.C.V is Microhematocrite method

(capillary tube method) that done by taken blood sample from single

puncture at the tip of the finger by capillary tube then put it in


Factors affecting PCV

• a) Physiological:

1- Higher in fetus and newborn than adult due to:
• bone marrow all still red marrow.
• Presence of HbF that have high affinity to O2 leads to relative hypoxia that
stimulate erythropoiesis.
2- Higher in male than female:
• Androgen hormone in male stimulate erythropoiesis.
3- Higher in large vessel than small one:
• Due to skimmed plasma
4- Higher in venous blood than arterial:
• Due to Cl shift phenomenon Vol of RBCs in venous < arterial by 3%

• b) Pathological:

1. Decreased in:

▪ Anemia due to decreased RBCs.
▪ Overhydration due to increased plasma volume.

2. Increased in

▪ Polycythemia due to increased RBCs.
▪ Dehydration due to decreased plasma volume.
Note: P.C.V. is physiologically higher in venous blood than arterial blood

• Note

Hemoglobin Content:
Definition: it is the amount of hemoglobin present in 100 c.c. (ml) blood.
Normal value: -Adult male 16 gm %
-Adult female 14 gm

Blood indices

• 1) Mean corpuscular volume (MCV):-
Definition: It is the average volume of a single RBC.
𝐇𝐞𝐦𝐚𝐭𝐨𝐜𝐫𝐢𝐭𝐞 𝐱 𝟏𝟎
MCV= -------------------------------------------
𝐑𝐁𝐂𝐬 𝐜𝐨𝐮𝐧𝐭/𝐦𝐦 𝟑 𝐢𝐧 𝐦𝐢𝐥𝐥𝐢𝐨𝐧𝐬
Normally =45 x 10 /5 = 90 μ3 cubic micronons (Femtoliter)
Normal range = 90 ±7 μ3

• 2) Mean corpuscular hemoglobin (MCH):
Definition: it is the average amount of hemoglobin in a single RBC.
𝐇𝐞𝐦𝐨𝐠𝐥𝐨𝐛𝐢𝐧 𝐜𝐨𝐧𝐭𝐞𝐧𝐭 𝐱 𝟏𝟎
MCH= ---------------------------------------
𝐑𝐁𝐂𝐬 𝐜𝐨𝐮𝐧𝐭/𝐦𝐦 𝟑 𝐢𝐧 𝐦𝐢𝐥𝐥𝐢𝐨𝐧𝐬
Normally = 15 x 10 /5 = 30 picogram (pg)
Normal range= 30 ± 3 pg

• 3) Mean corpuscular hemoglobin concentration percent (MCHC):
• It is the amount of hemoglobin in 100 ml packed RBCs.
𝐇𝐞𝐦𝐨𝐠𝐥𝐨𝐛𝐢𝐧 𝐜𝐨𝐧𝐭𝐞𝐧𝐭 𝐱 𝟏𝟎𝟎
MCHC= -----------------------------------------
Normally = 33% (normal range 33 % ± 3)