Lapis ISSN 2398-2969

Hematology: packed cell volume

Synonym(s): PCV, Hematocrit

Contributor(s): Michael Waters, Molly Varga, Vetstream Ltd

Overview

  • High-speed centrifugation of whole blood separates layers of cells:
    • Erythrocytes.
    • Buffy coat (thrombocytes, leukocytes and nucleated erythrocytes).
    • Plasma.
  • Measurement of these components is an indicator of the patient's erythrocytic and hydration status.
  • PCV is measured from a spun sample.
  • Hematocrit is usually calculated by automated counters from cumulative cell volumes of counted RBCs.

Sampling

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Tests

Methodologies

Wintrobe method
  • Hematocrit tube of uniform bore calibrated longitudinally into 10 cm or 100 mm. Numbers on the right read from 0-10 cm and are used to determine PCV. Numbers on the left are used for erythrocyte sedimentation rate.
  • Fill the tube to the 10 cm mark with a well-mixed sample of blood in anticoagulant, ensuring that there are no bubbles.
  • Centrifuge sample at 3000-4000 rpm for 30 min.
  • The scale is then read at the top of the packed erythrocytes adjacent to the buffy coat. The number is multiplied by 10 to express PCV as % (SI units   →   expressed as l/l).

Microhematocrit method

  • Fill a plain capillary tube with anticoagulated blood to 1 cm from the end and wipe the outside of the tube. Seal the vacant end of the tube with clay, plastic or by heating. If blood is taken directly from the animal (ear tip, nail, etc), use heparinized tubes.
  • Using a microhematocrit centrifuge, spin for 5 min at 10,000 rpm or 2 min at 16,000 rpm.
  • Read the PCV using one of a variety of microhematocrit readers.
  • Advantages: small volume of blood required, quick to perform.

Automatic counters

  • Automatic counters calculate the hematocrit from the cumulative volume of the cells counted.

Availability

  • Widely available at commercial laboratories.
  • Facilities to measure PCV should be available in all practices.

Validity

Sensitivity

  • Very sensitive.

Specificity

  • High.

Predictive value

  • Good.

Technique (intrinsic) limitations

  • Does not give direct information of red cell indices or of hemoglobin concentration.

Result Data

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed papers

  • Recent references fromPubMed.

Other sources of information

  • Campbell T W & Ellis C K (2007)Avian and Exotic Hematology and Cytology.3rd edn. Wiley-Blackwell. ISBN: 978-0813818115.
  • Fudge A M (1999)Laboratory Medicine. Avian and Exotic Pets.W B Saunders Co. ISBN: 0721 676 790.


ADDED