Fundamentals of Analytical Toxicology. Robin Whelpton

Fundamentals of Analytical Toxicology - Robin Whelpton


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of biological samples. Such staff should be vaccinated against hepatitis B, polio, tuberculosis, and tetanus, and possibly other diseases in specific countries. Sample handling should be performed with due attention to preventing droplets splashing into the eyes and minimizing aerosol formation (wear eye protection, perform mixing and other procedures in a microbiological safety cabinet, always use either sealable centrifuge tubes or a centrifuge with sealable rotors). Screw-capped sample tubes are preferable to those with push in stoppers because there is less risk of aerosol formation when opening the tube.

       2.2.2 Clinical sample types

       2.2.3 Blood and blood fractions

       2.2.3.1 Arterial blood

       2.2.3.2 Venous blood

      Venous blood is obtained by venepuncture of (usually) the median cubital vein of an arm remote from any infusion site. Either a hypodermic needle and syringe (1–50 mL) or a commercial vacuum-sampling system such as a VacutainerTM may be employed. Care should be taken to ensure that 2-propanol or other alcohols are not introduced into the sample when using swabs to clean/disinfect the skin. A tourniquet can be used to distend the vein prior to venepuncture, but should be released immediately prior to sampling.

Blood & related fluids Blood (‘whole blood’) is the fluid that circulates through the arteries, capillaries, and veins. The adult human body contains some 5–6 litres of blood. It is composed of plasma and blood cells. Normally venous blood is obtained (Section 2.2.3.2). If whole blood is to be analyzed, then the sample should be collected into an appropriate anticoagulant, mixed, and then frozen in order to lyse the cells before the analysis. Dried blood spots (DBS) are the residues remaining when whole blood has been allowed to dry on filter paper or another appropriate medium. Post-mortem blood is blood obtained after death, usually at autopsy. The site of sampling should always be recorded (Section 2.3.2.1). [N.B. Occult blood is altered blood found only in trace amounts particularly in faeces. It is not used as an analytical sample.]
Blood cells include red cells (erythrocytes) and white cells (lymphocytes, leucocytes, platelets, etc.). All may be harvested from freshly collected blood with appropriate procedures (Section 2.2.3.5)
Cerebrospinal fluid (CSF) is a plasma ultrafiltrate (i.e. its composition is that of plasma except that high Mr proteins are absent) that surrounds the elements of the central nervous system (CNS). It is obtained by lumbar puncture (needle aspiration from the spinal cord) and is usually collected into sterile tubes. Samples contaminated with blood should be discarded if microbiological assessment is required
Cord blood is blood obtained from the umbilical cord at parturition. Normally venous cord blood is obtained in order to reflect neonatal, as opposed to placental, blood. It may be possible to obtain plasma or serum depending on the volume available
Plasma is the liquid portion of blood (Section 2.2.3.4). It is obtained by centrifugation of anticoagulated whole blood
Serum is the pale yellow fluid remaining when whole blood has clotted. Its composition is generally the same as plasma except that fibrinogen and factors associated with the clotting process are absent (Section 2.2.3.3). It is obtained by centrifugation of whole blood that has been allowed to clot in the sample tube
Body fluids other than blood Amniotic fluid is the fluid that surrounds the foetus in the amniotic sac
Aqueous humour is the watery fluid occupying the space between the cornea and the iris of the eye
Bone marrow aspirate is a sample of the spongy tissue found within bones that produces blood cells
Breast milk is the protein and fat-rich fluid produced by nursing mothers. The first expression of breast milk (colostrum) is especially rich in protein
Gastric aspirate is an acidic aqueous fluid containing digestive enzymes, food residues, etc. obtained by aspiration from the stomach
Intraosseous fluid is fluid derived from blood and interstitial fluid residing within bones
Interstitial fluid is the fluid between blood vessels and cells
Lymph is a yellowish fluid in the lymph channel secreted from the lymph glands
Pericardial fluid is fluid present between the heart and the sac surrounding the heart known as the pericardium
Peritoneal fluid is the fluid that accumulates in the peritoneum