TYPES OF SPECIMENS

Blood is a suspension of cells in a protein-salt matrix. Plasma: The non cellularportion of blood contains a series of proteins, some of which are involved in the coagulation process. Serum: the non-cellular fluid, which can be separated from the clotted material

Blood used for biochemical analysis is ollected from the veins,arteries or capillaries. For most testing, the site of phlebotomy has no analytical or physiological significance, so that venous blood is utilized because of ease of collection. For

Most testing is performed on the liquid or serum fraction of the blood that has been allowed to clot. The assumption is made that the distribution of constituents between cellular and extracellular compartments of blood is roughly equal. For some analytes it may be necessary to prevent the blood clotting process using an anticoagulant and the separated liquid (plasma) will be then used for analysis

Glucose changes most rapidly of all cells constituents when serum or plasma is left in contact with RBCs. Since glycolysis is an enzyme catalysed reaction, sodium fluoride has to be added to the blood sample for glucose estimation to inhibit the enzyme "enolase" that is involved in glycolysis.

Collection of Urine Specimens Single specimen of urine is used for general urine examination and for most qualitative tests. For quantitative work, 24 hour specimen is best employed, except when collecting specimens as part of tests such as Dxylose test.

Collection of Urine Specimens For collecting a 24h sample, the patient empties the bladder first and the urine is discarded. All specimens passed thereafter during the day and during the following night are saved and the specimen obtained by emptying the bladder at the same time the following morning is added to them. The sample is collected in a clean covered container and kept in a cool place preferably in the refrigerator.

Anticoagulants 1- Heparin: a-mucoitin polysulphuric acid inhibits the formation of thrombin from prothrombin. It is usually available as the Na, K, NH4 and Li salts. 2- EDTA (Ethylene diamine tetra acetate): It chelates calcium ions which are essential for clotting mechanism. Its dipotassium and dilithium salts are most often used. 3- Oxalate and citrate: Oxalate acts by precipitating the calcium. Potassium oxalate is the most soluble and so it is most commonly used. Sodium citrate does not precipitate calcium but converts it into a non-ionised form. 4- Sodium flouride: It is also considered as an anticoagulant, but since larger amounts are needed, it is rather used as a preservative for glucose determination by inhibiting red cell metabolism, glycolysis and bacterial action.

Other Body Fluids The laboratory is also called upon to perform a variety of testing on cerebrospinal fluid, amniotic fluid and other body fluids. In all instances, it is essential to ensure that the proper specimen is collected and contamination is avoided. In addition, biochemical analysis may be performed on stool samples, gastric aspiration, and renal or biliary calculi. Stool samples are usually collected over h periods. Renal calculi (stones) collection may be a random event depending on when the stone is passed.