PACKED CELL VOLUME (HEMATOCRIT).

PACKED CELL VOLUME (HEMATOCRIT)

  • Hematocrit literally means “blood separation”
  • Packed cell volume is the percentage of volume of blood occupied by the red cells
Methods used for determination of PCV
  •  Macrohematocrit method (Wintrobes method)
  • Microhematocrit method
  • Electrical method
  •  Indirect method 
 Wintrobes method for estimation of PCV
  • Apparatus required
    • Wintrobes tube –
      •  It is 110mm long, narrow, thick walled tube with 3mm internal bore
      •  Graduated from 0 to 10 cm with graduation on both sides in ascending and descending order on 2 sides of tube
      • Scale with the markings from 0 to 10 from above downwards is used in ESR determination and from below upwards is used for PCV determination
    • Pasteur pipette
    • Centrifuge
  • Procedure –
    • 2ml of venous blood is collected and mixed with double oxalate (ammonium oxalate and potassium oxalate) or EDTA powder in the proportion of 1.5mg/ml
    •  Blood is drawn into Pasteur pipette and introduced in the Wintrobes tube from the bottom to 0 or 10 mark above
    •  Place the Wintrobes tube in the centrifuge machine and other Wintrobes tube filled with water on the opposite side so as to balance it. 
    • Centrifuge the tube at the speed of 3000rpm for 30 minutes 
    • After 30 minutes stop the centrifuge, take out the tube and note the readings
    •  Calculation –
      •  Hematocrit = [ Height of RBC’s in mm/Height of RBC and plasma] X 100
 Zones separated after centrifugation
  •  Top layer – Plasma (48 – 52%)
    •  Normally amber or pale yellow colour
    • yellow – jaundice
    •  Pink or red colour indicates – hemolysis
    • creamy white – hyperlipidemia
    • Brown coloured – meth hemoglobinemia
    • Cloudy (increased viscosity) – Multiple myeloma
  • Intermediate zone – Buffy coat – Zone of platelets and leukocytes (2% – 3% or 1mm thick)
    • Greyish – white tan layer
    •  Smears prepared from buffy coat can be used to diagnose
      •  Sub leukemic leukemia
      • LE cells 
      • Detection of plasma cells
      •  Hemoparasites
  • Lower most zone or bottom layer – Zone of packed RBC’s (45% – 50%)
  • Normal PCV 
    • Males – 40 -50%
    •  Females 37 – 47%
    • New born – 55 – 60%
  • Clinical implications of PCV
  •  PCV is affected by the number of RBC’s, their size and plasma volume
  •  High PCV – 
    •  increased number of RBC’s
    • Increase in size of RBC
    • Decrease in plasma volume
  • Low PCV 
    • Decrease in number of RBC’s
    • Decrease  in size of RBC
    • Increase in plasma volume
  • Causes of increased PCV
    • Polycythemia vera
    • High altitudes 
    • Hypoxia conditions 
    • Lung and heart diseases
    • Dehydration
    • Burns (due to loss of plasma)
  • Causes of decreased PCV 
    • Anemia
    •  Conditions with increased WBC’s 
    •  long term illness,
    • infection
    • leukemia
    • Lymphoma
    •  Hemodilution or overhydration 
    • Acute kidney disease – lower erythropoietin production leads to less RBC’s production by bone marrow
    •  Pregnancy
References 
1.      Praful B. Godkar, Darshan P. Godkar.Textbook of medical laboratory technology 2007. Second Edition
2.      Sabitri sanyal, Aparna Bhattacharya.Clinical pathology A practical manual 2017. Third edition.