The scientific study or diagnostic examination of the blood serum, especially with regard to the response of the immune system to pathogens and introduced substances. Serological tests may be performed for diagnostic purposes when an infection is suspected in Rheumatic illnesses, and in many other situations, such as checking an individual’s blood type
For the detection of this unknown substance from patient’s specimen, the specimen should be collected and prepared appropriately. In addition the equipment that is used for testing should be free from any contaminants so as to get true result. The following are some of the equipment used in routine serology.
Dirty glassware easily affect serological test. After using all the glass wares (test tube, beaker, pipette, etc.) they should be socked in detergent for several hours and rinsed several times in tap water. Finally allow drying by placing in a dry oven or dust free place. Test tubes and pipettes should not be scratched or broken, which will interfere with the reading of a test.
Types of glassware include:
• Test tube
• Glass slides
• Serologic pipette with a size of l0ml, 5ml, 2ml and 1ml.
Constant temperature device
Incubator and water bath are usually used in serologic tests. These materials are electrically operated and have thermostat that hold the temperature within the required limits. These devices should be checked prior to use by installing a thermometer
Rotating machines are required to facilitate antigen antibody reactions. Such machine has a flat plate, which rotate at a prescribed rate of speed. A knob located on the front part of the machine controls the number of revolution per minute.
Collection Preparation and Preservation of Specimen for Serologic Tests
Specimens that are used for serologic test include: serum, plasma and cerebrospinal fluid. Serum or plasma sample could be obtained from venous blood, which can be performed by the laboratory personnel however. Cerebrospinal fluid should be collected by a physician or a trained nurse. For serum or plasma sample, first 2-3 ml of venous blood is collected using sterile syringe and needle from a patient.
If serum is required, allow the whole blood to clot at room temperature for at least one hour and centrifuge the clotted blood for 10 minutes at 2000 rpm. Then transfer the serum to a labeled tube with a pasture pipette and rubber bulb.
Plasma sample is obtained by treating fresh blood with an anticoagulant, centrifuge and separate the supernatant.
The specimen should be free from hemolyzed blood. Finally, seal the specimen containing tube; the tube should be labeled with full patient’s identification (Age, Sex, code no, etc). The test should be performed with in hours after sample collection, if this could not be done preserve it at- 200°c.
Shipment of Serological Specimen
Most health center and clinic laboratories often are limited in the diagnostic procedures that can be carried out and have to ship serologic specimens to other laboratories.
Before shipment the following things should be considered.
• Don’t ship whole blood unless the tests to be performed require whole blood.
• Do not inactivate serum or plasma before mailing.
• Keep the specimen and packing container in the refrigerator until time of shipment but if shipment requires several days, freeze the specimen.
• Then ship the specimen by the fastest route.
Complement inactivation is important because it is known to interfere with different tests. In activation of complement can be achieved by heating the serum or plasma at 560°C for 30 minutes. If more than four hours has elapsed since inactivation, a specimen should be re-inactivated with same temperature 10 minutes.
Dilution is the act of making a weaker solution from a stronger one. This is usually done by adding a water or saline, which contains none of the material being diluted. Dilution is usually expressed as one unit of the original solution to the total number of units of final solution. Serial dilution means decreasing the volume of serum progressively by maintaining a constant volume of fluid most commonly, serial dilutions are two fold, that is, each dilution is half as concentrated as the preceding one. The total volume in each tube is the same.
Determination of Endpoint and Titer
The reciprocal of the greatest reacting dilution of the serum is considered as the measure of titer or the concentration of the antibody. For example, it the highest dilution of the serum that shows a visible reaction is at 1:32 dilution, the titer of the test is expressed as 32.