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 andduring 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.