Quality assurance in the laboratory

Quality assurance in the laboratory includes all aspects of the analytical work, from correct identification and preparation of the patient to ensuring that the laboratory result goes back to the doctor.

The prime objective of quality assurance is to ensure that the laboratory provides results that are correct and relevant to the clinical situation of the patient.

The 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).

1. Specimen collection

The appropriate collection of specimens is of utmost importance if the laboratory results are to be relevant to the clinical situation of a patient. When material is collected for the purpose of monitoring and control of treatment of patients, the following factors should be considered:

— the physiological state of the patient (e.g. the reference ranges of certain indicators vary with age and sex);

— the appropriate preparation of patients for specimen collection (e.g. blood for the measurement of glucose and lipids should be taken in the morning from a patient who has fasted for 12 hours, because their concentrations are elevated after a meal);

— the appropriate tools for specimen collection (e.g. blood for cell counting should be collected in tubes containing EDTA dipotassium salt to avoid plasma coagulation and platelet aggregation);

— the appropriate site for specimen collection (e.g. the concentration of glu- cose is different in arterial and venous blood).

Specific aspects of specimen collection, including those for the detection of infec- tive organisms (bacteria and parasites), are outlined in the relevant sections of this manual.

To ensure that the most useful specimen is obtained, it should always be collected at the appropriate time. Random collection should be limited to emergency situa- tions. For example, sputum specimens for the detection of tubercle bacilli should be collected in the early morning, while urine for the diagnosis of schistosomiasis and other conditions should be collected as a “terminal” urine specimen (see sec- tion 7.2.8).