What is the function of the capillary tube in hematology?

Function of the Capillary Tube in Hematology

Capillary tubes play a crucial role in the field of hematology, which is the study of blood, its diseases, and its components. These slender tubes are essential for conducting various blood tests, particularly in measuring the packed cell volume (PCV) or hematocrit level, which is the proportion of blood volume that is occupied by red blood cells.

Key Functions

  • Separation of Blood Components: When blood is placed in a capillary tube and centrifuged, it separates into layers. This separation is critical for analyzing the relative proportions of plasma, white blood cells, and red blood cells.
  • Measurement of Hematocrit Levels: The capillary tube is used in the microhematocrit method to measure the volume percentage of red blood cells in blood. This is vital for diagnosing and monitoring conditions like anemia or polycythemia.
  • Micro-Sampling: Capillary tubes are ideal for micro-sampling, which is the collection of very small amounts of blood. This is particularly useful in pediatric tests where blood volume is limited.


  • Minimal Blood Required: The small size of capillary tubes requires only a tiny amount of blood, reducing the discomfort for patients.
  • Precision: They allow for precise measurements and analyses of blood components, aiding in accurate diagnosis and treatment planning.
  • Versatility: Capillary tubes can be used for several other purposes in hematology and laboratory diagnostics, including blood coagulation tests and the measurement of specific blood components.

In summary, capillary tubes are indispensable tools in hematology, enabling detailed blood analysis with minimal patient discomfort and high precision. Their use in measuring hematocrit levels and other blood components is critical for diagnosing and managing various blood-related conditions.

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