Hematocrit (Hct)

Sample

1. The patient blood is taken in EDTA.
2. It is stable for 48 hours at 4 °C and 6 hours at 23 °C.
3. Fetal blood: Collected by percutaneous blood sampling.

Precautions for Hematocrit

1. Perform the test within 6 hours of the blood collection.
2. EDTA is the choice of blood anticoagulant.
3. Avoid hemolysis.
4. Avoid clotting of the blood.
5. Centrifugation must be adequate. This will give a high result.
6. The buffy coat is not included in the hematocrit.
7. Avoid excess of the EDTA.
8. Avoid overdilution of the blood sample by the anticoagulant.
9. Avoid Prolonged tourniquet, it can lead to hemoconcentration and error in the Hct.
10. Drugs like penicillin and chloramphenicol decrease the Hct level.

Purpose of the test (Indications)

1. It is used to diagnose anemia.
2. Hct is done in patients with bleeding or blood loss.
3. It is part of a complete blood count.

Definition of hematocrit (Hct)

After the centrifugation of the EDTA blood in the test tube. Now the % of the RBC column to the original whole blood volume is called hematocrit (Hct).

Principle of hematocrit (Hct)

1. The word hematocrit means to separate the blood where the plasma and blood cells are separated.
2. This test gives information about RBC concentration and is helpful to see hemoconcentration.
3. This is basically a measurement of total blood volume and RBCs ratio as a percentage.
   1. In a capillary tube or Hct tube blood is centrifuged. Cells mainly RBCs will settle down and clear plasma appears on top.
   2. Now, this is the ratio of settled cells and upper clear plasma and calculated in %.

Quality control of the Hemoglobin:

1. This hemoglobin quality control can be done by checking Hb results in g/dL by comparing the result with hematocrit results.
2. Hct results in % units, using the following formula:

3. One g/dL Hb  unit = 3 Hct unit
   1. For example, if the Hb is 13 g/dL
   2. Then Hct is = 13 x 3 = 39 %
4. Now compare the result with the Hct value.

Factors that will affect Hematocrit are :

1. Abnormalities of RBCs morphology will affect Hct.
2. Raised values of WBC will alter the Hct.
3. People from high altitudes have increased Hct.
4. After the hemorrhage values are not reliable.
5. Dehydration and hemodilution will affect the Hct.
6. Pregnant ladies will have low values due to hemodilution.
7. Chloramphenicol and Penicillin decreased value.

Pathophysiology of Hematocrit (Hct)

1. Hct is a macroscopic observation where the percentage volume of the packed RBCs is measured.
   1. This is also called packed cell volume or PCV.
   2. The Hct closely reflects the hemoglobin and RBC values.
   3. Hct mostly depends upon the number of RBCs
2. The word hematocrit means to ‘separate blood’ where blood cells and plasma are separated by centrifugation.
3. While in electronic counters, it is calculated by MCV.
4. A calculated Hct is lower 2% than the microhematocrit due to trapped plasma in a centrifuged column of RBCs.
5. Hct is lower in pregnant women than nonpregnant ladies.
   1. Females have less Hct than men.
6. Hct is usually three times the Hb concentration in grams/dl.
7. Decreased values indicate anemia.
8. Increased values indicate erythrocytosis.
   1. In dehydration, Hct will be falsely high due to less plasma volume and the number of RBCs is the same.
   2. In the case of large-size RBCs, the Hct will be falsely high.
9. Blood transfusion is not recommended if the Hb is >8 g/dl or Hct is >24 %.
10. Hct is more reliable and useful than the RBCs count.

Method to estimate the Hct:

1. Microhematocrit tube method. These are as correct as of the tube method.
2. Wintrobe hematocrit method is the macro method.
3. Automated method.
   1. In an automated machine, it is calculated RBCs count and MCV.
   2. Hct = Hb x 3
   3. Hb = RBC in million x 3
   4. Hct = RBC in million x 9
   5. This formula depends upon the value of MCHC (33).
      1. This factor varies depending upon the MCHC from 2.7 to 3.2.

Source 2

Age	Hct %
Newborn	44 to 64
2 to 8 weeks	39 to 59
2 o 6 months	35 to 50
6 to 12 months	29 to 43
1 to 6 years	30 to 40
6 to 18 years	32 to 44
Adult
Male	42 to 52
Female	37 to 47
Pregnant females	>33
Old people	Values may slightly decrease

Source 4

Fetal ( 26 to 30 weeks )	41 to 54 %
cord blood ( 9 months+ )	32 to 40 %
Children
0 to 2 weeks	44 to 64 %
2 to 6 months	35 to 49 %
6 months to 1 year	29 to 43 %
1 to 6 years	30 to 40 %
6 to 18 years	32 to 44 %
Men	42 to 52%
Women	36 to 48%
Pregnant females	> 33 %

Significance

1. Decreased values are an indicator of Anemia.
2. Decreased values are also seen in, Leukemia, Lymphoma, Hodgkin’s disease. and Myeloproliferative disorders.

Raised Hct is seen in:

1. Polycythemia Vera.
2. Erythrocytosis.
3. Extreme physical exercise or excitement.
4. High Altitude.
5. Dehydration leads to Hemoconcentration e.g. diarrhea, burns, and vomiting.
6. Congenital heart failure.
7. Severe chronic pulmonary obstructive disease (COPD).

Decreased Hct is seen in:

1. Anemia.
2. Hemoglobinopathies.
3. Cirrhosis.
4. Hemolytic anemia (Erythroblastosis fetalis, drug-induced hemolytic anemia, and paroxysmal nocturnal hemoglobinuria.
5. Hemorrhage.
6. Bone marrow failure
7. Renal diseases.
8. Normal pregnancy.
9. Autoimmune diseases.
10. malignancies like lymphoma, leukemia, multiple myeloma, and Hodgkin’s diseases.
11. Normal pregnancy.
12. Bone marrow failure.

Critical value of Hct = <15 % or >60 %.

---