Manual of basic techniques for a health laboratory - libdoc.who.int

102 Manual of basic techniques for a health laboratoryThe stages at which quality assurance should be applied include:— preparing the patient— collecting the specimen— handling and dispatch of the specimen (see sections 2.6.1 and 3.7)— control of methods and reagents (see individual methods)— calibration of equipment (see section 2.5)— reporting results (see section 2.6.2).3.9.1 Specimen collectionThe appropriate collection of specimens is of utmost importance if the laboratoryresults are to be relevant to the clinical situation of a patient. When material iscollected for the purpose of monitoring and control of treatment of patients, thefollowing factors should be considered:— the physiological state of the patient (e.g. the reference ranges of certainindicators vary with age and sex);— the appropriate preparation of patients for specimen collection (e.g. bloodfor the measurement of glucose and lipids should be taken in the morningfrom a patient who has fasted for 12 hours, because their concentrations areelevated after a meal);— the appropriate tools for specimen collection (e.g. blood for cell countingshould be collected in tubes containing EDTA dipotassium salt to avoidplasma coagulation and platelet aggregation);— the appropriate site for specimen collection (e.g. the concentration of glucoseis different in arterial and venous blood).Specific aspects of specimen collection, including those for the detection of infectiveorganisms (bacteria and parasites), are outlined in the relevant sections of thismanual.To ensure that the most useful specimen is obtained, it should always be collectedat the appropriate time. Random collection should be limited to emergency situations.For example, sputum specimens for the detection of tubercle bacilli shouldbe collected in the early morning, while urine for the diagnosis of schistosomiasisand other conditions should be collected as a “terminal” urine specimen (see section7.2.8).