Packed cells volume (PCV) or Hematocrit, is defined as the percent of blood occupied by RBCs, or simply you can define PCV as the percent of RBCS in whole blood.

To measure PCV, the RBCS must be packed together in one layer, which can be achieved by centrifugation of whole blood sample. it is essential also that blood used for hematocrit to be collected on anticoagulant as EDTA, it is contraindicated to used anticoagulant in solution as sodium citrate to measure the PCV%.



Generally, when a whole blood sample (Blood sample collected on anticoagulant) is centrifuged, the blood is separated into three layers, which are PCV, Buffy coat and plasma layers. You can calculate the PCV% (RBCs %) by measuring the length of the PCV layer and divide it on the length of the whole blood column, the result is multiplied by 100.


PCV% is used to calculate the mean corpuscular volume (MCV). PCV also is used as a rapid indicator for the internal homeostasis of the body, usually normal PCV% indicates normal homeostasis, but because PCV layer is formed from packed RBCs, PCV % may become normal in abnormal conditions as:

The presence of both macrocytic erythrocytes and Oligocythemia at the same time.
The presence of both dehydration and Oligocythemia.
The presence of both dehydration and microcytic erythrocytes.
From the above paragraph, it is clear that you can’t depend on PCV alone for interpretation of erythrocytes picture.


Causes of increase PCV
PCV layer is increased in the following conditions:


Dehydration as in cases of severe diarrhea, polyuria, excessive vomiting and Ruminal acidosis Polycythemia (increased RBCs count). Chronic obstructive pulmonary disease, which is associated with increased RBCs. Pulmonary diseases that associated with hypoxia. Physiological conditions as high altitude.

Causes of decease PCV
PCV layer is decreased in the following conditions:

Oligocythemia (Decrease the number of RBCs). Microcytic hypochrmic anemia, due to decrease MCV. Renal failure, as a result of decreased secretion of erythropoietin. Dilution of blood (After fluid therapy).

As mentioned above, after centrifugation of whole blood, three layers will form; the PCV, Buffy coat and plasma layer. The manual methods that used for calculation of PCV %, are also helpful for interpretation of leucocytes and for diagnosis of diseases that associated with change in the color of plasma.

Buffy coat
Buffy coat is the white layer that present just above the PCV layer and formed mainly from leucocytes and platelets, Buffy coat is increased in leucocytosis and decreased in leucopenia. Buffy coat can be used as a useful indicator for the leucocytes count.

Plasma layer
Abnormal change in the color of plasma can be detected after centrifugation of blood for PCV, dark yellow color of plasma may indicate Jaundice, milky color indicates lipemia and pink color indicates hemolysis. In other words, the color of plasma can help in: a) as indicator for hemolytic, hepatic and obstructive jaundice. b) The pink color of plasma is indicative for hemolysis of erythrocytes, which associate some diseases as bacillary hemoglobinuria and blood parasites as Babesia species. c) Milky color of plasma indicates the increase of lipids in blood.

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