Basic Blood Tests

by Rachel Bhan

The Complete Blood Count (CBC) is one of the most commonly performed tests. Cbc blood tests are routine tests used to evaluate the blood and general health. Blood acts as a medium for providing oxygen and other nutrients throughout the body, and draws waste back to the excretory systems for elimination. In this, blood laboratory test blood is obtained from the patient's veins by venipuncture or fingerprick. A CBC measures all the following parameters: red blood cell count (RBC), white blood cell count (WBC), hemoglobin, hematocrit, three red cell indices, and the white cell differential. Platelet counts are sometimes included in a CBC.

The Red blood cell (RBC) count is the number of RBCs in a cubic millimeter of blood. The RBCs are the cells produced in the bone marrow that act as a carrier of oxygen to the tissues. The normal range is 4.5- 5.9 million/mm3 for men and 4.0-5.3 million/mm3 for women. A person with a drastically low RBC count can have symptoms of fatigue and shortness of breath. A decrease in the RBC count results in a decrease in the hemoglobin and hematocrit values.

The White blood cell (WBC) count is the number of WBCs in a cubic millimeter of blood. The WBCs prevent and fight invaders. Various specific types of WBCs are measured in the white cell differential. Normal WBC count is from 4,500 to 1,000. The WBC count can be decreased by medications, stress, decreased production of WBCs in the bone marrow and minor viral infections.

Oxygen is carried to the tissues by hemoglobin in the RBC. A normal hemoglobin level is 14.0-18.0 g/dl for men and 12.0-16.0 g/dl for women. Any drug which causes a suppression of the bone marrow, will decrease the hemoglobin level. Deficiency leads to anemia. Hematocrit is the percent of the cellular components in the blood to the fluid or blood plasma. Normal values for men are 40- 54% and for women 37-47%. A decrease in hematocrit is always seen with a decrease in the hemoglobin.

The mean cell volume or MCV is the most imperative of the RBC indices. It is a measure of the average size of the RBC. Deficiency of Vitamin B12 and Folic Acid cause increases in MCV. Normal MCV levels are 80-96. Platelets are cellular fragments essential for blood clotting. Normal platelet values are 150,000-350,000.

The white cell differential counts 100 white cells and differentiates them by type. The three main types are: polymorphonuclear cells (or PMNs), lymphocytes, and monocytes. Normal value of PMNs is 55-80%. 25-33% is the normal number of lymphocytes, and 3-7% is normal for monocytes.

Cholesterol levels are vital indices for determining the heart condition. Normal cholesterol levels are 150-250 mg/dl.

Two tests which measure kidney function are the Blood urea nitrogen (BUN) and Creatinine. Normal BUN levels are 10-20 mg/dl. Normal levels of creatinine are 0.6-1.2 mg/dl. Test results are usually interpreted based on their relation to a reference range.

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