Hematocrit test (HCT-PCV): procedure, range, result

The hematocrit test is an important test for estimating the average volume of red blood cells. Anticoagulated blood is used for hematocrit tests.

We can calculate mean corpuscular volume (MCV) with the help of HCT.

Hematocrit test (HCT-PCV) procedure, range, result
Hematocrit test (HCT-PCV)

What is the difference between HCT(Hematocrit) and PCV (Packed cell volume)?

when anti-coagulated blood is centrifuged, red blood cells are packed at the bottom. These Red blood cells are expressed as the RBC volume of centrifuged blood. This call is called a PACKED CELL VOLUME (PCV).

On the other hand, when this Packed cell volume is expressed in percentage (%) of total centrifuged blood, it is called Hematocrit (HCT)

Hematocrit test procedure

There are two methods for calculating the hematocrit.

  1. Macro Method (Wintrobe’s Method)
  2. Micro Method

Wintrobe’s method of Hematocrit (HCT)

It is an old method of HCT estimation, now the micro method is used.

Test Requirements

  1. Wintrobe tube
  2. Centrifuge (15 cm internal radius)
  3. Pasture pippet

Hematocrit test Procedure

  1. Fill the tube up to the maks of 100 with EDTA anti-coagulated blood.
  2. Centrifuge the tube at 3500 rpm for 30 minutes.
  3. Carefully take the tube from the centrifuge and note the level of packed RBC (Buffy coat should not be included).

Note: If packed cell volume is above the 0.5 L/L, centrifuge again for 30 minutes.

Advantage of macro-method

Dis-Adventage macro method

  1. The macro method requires a large amount of blood as compared to the micro method.
  2. Centrifugation time is long (30 mint).
  3. This method is not 100% accurate.

Micro Method for HCT estimation

It is an advanced method of hematocrit calculation.

Requirements

  1. 75 mm length with 1 mm bore longe tube.
  2. Microheamtocrit centrifuge
  3. Microhematocrit Reader
  4. Plasticine

Procedure

  1. Fill the tube with blood.
  2. Seal one end of the tube with plasticine.
  3. Place the tube in the Microheamtocrit centrifuge.
  4. Centrifuge for 4 to 5 minutes.
  5. Take the tube from the centrifuge and place it in the microhematocrit Reader and note the packed cell volume (PCV).

Advantage of micro method

  1. Small quantity is sufficent for the test (Macro method need large).
  2. Less centrifuge time is requiered in micro-method.
  3. One than one sample can be run at a time.
  4. It is accurate as compare to Macro method.

Dis-Adventage of micro method

  • It needs Microhematocrit Reader.
  • Microheamtocrit centrifuge is necessary for the micro method.

Sources of error in Hematocrit test (PCV/ HCT)

  1. Sample collecting error.
  2. Incorrect amount of anti-coagulant.
  3. Incorrect filling of the tube.
  4. A clot in the sample.
  5. Hemolysis sample.
  6. Variation in the internal diameter or bore of the tube.

Low Hematocrit

Hematocrit link with Red blood cell concentration in the blood. When RBC increase, Hematocrit will raise. When RBC decrease, Heamtocrit will decrease. In case of anemia. hematocrit will be less than normal due to less quantity of red blood cells.

High Hematocrit

Hct will raise when red blood cells increase. Some diseases are like Polycythemia. Red blood cells increase, as a result, Hematocrit will increase.

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