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Laboratory tests performed in hematology area involve the blood cells, red blood cells (erythrocytes), white blood cells (leukocytes), and the platelets (thrombocytes). The main source of blood cells is the bone marrow, although the lymph nodes and the spleen contribute some of the white blood cells.

Cells and their constituents, their number or concentration, the relative distribution of different cells, their structural or biochemical abnormalities that contribute to the disease are measured by hematological tests.

A disease can be diagnosed by hematological analysis or the treatment can be monitored by laboratory analysis. Blood disorders can be monitored by hematological manifestations and diseases can have hematological basis. Anemia and enlarged lymph nodes are the examples of symptoms causing many diseases. CBC or complete blood count is the hematological profile generated by automated instruments and it is the basis of initial evaluation and follow-up of the patient

Skin puncture or venipuncture is the primary method collection of specimens for hematology and it is important to show cordial approach to the patient in general. Capillary blood Capillary blood collection can be used for many tests including hemoglobin, microhematocrit, red cell, white cell, and platelet counts. Capillary blood can be also used for the preparation of blood smears for microscopic analysis. It is important not to touch the sampling device to the skin when the tip of the sampling device is placed in the drop of blood when collecting capillary blood.

The sampling device can be micropipette, microcuvette, or slide. The order of collection is an important consideration. Usually, blood for hemoglobin test is taken first, and then cell counts, and lastly blood films are prepared. Platelet counts, if needed should be done very first. Knowledge of correct collection techniques and pre analytical techniques like adequate mixing of blood with diluting fluid is important for accurate results.

Venous blood Many tests can be done with a tube of venous blood, including erythrocytes sedimentation rate which requires bigger volume of blood. Anticoagulant used commonly is ethylenediaminetetraacetic acid (EDTA). This preserves the cellular morphology and prevents coagulation.

Blood should be well mixed with the anticoagulant by gentle inversion 5 to 10 times immediately after it is collected, since even small clots are not acceptable for hematology. White cell counts, microhematocrit, platelet counts, and sedimentation rates can be determined upto 24hours after blood is collected in EDTA if it is refrigerated at 4 degree centigrade.

After collection, the specimen should be properly labeled and transported to the laboratory for analysis as quickly as possible for analysis. Standard precautions are complied during collection, laboratory handling, and testing using blood specimens. All samples are to be considered as potentially infectious, and the proper use of barrier-protective apparel and devices is mandatory.

Written by Phlebotomy Training specialist Dr Shahbaz A. Cheema, Course Director for Maxis Healthcare who run NHS Accredited Phlebotomy Training courses for medical and non medical practitioners. Learn the 3 Steps To Become a Phlebotomist