Depending on the type of sample, the analyte to be measured, and when the measurement will be performed, samples must be preserved under specific conditions. In some analyses, it is crucial that the sample is handled under specific temperature conditions from collection to measurement. Each laboratory is recommended to establish the necessary protocols for sample conservation, based on available data on the stability of the measured analytes.
Following specific work protocols established by the laboratory, samples must undergo preparation procedures prior to analysis, when necessary, according to the nature of the sample and the requested analysis. Once prepared, they must be preserved until the moment of analysis under appropriate conditions, avoiding cross-contamination.
The laboratory must review the samples and corresponding requests and record anomalous samples or those that do not meet established criteria. It must alert of incorrect or incomplete sample or request identification. It must also alert of inadequate sample or insufficient volume for the request. Some examples of inadequate samples are:
Coagulated samples
This may be due to slow collection, incorrect mixing of the anticoagulant with the sample, or a defect in the anticoagulant itself. This problem invalidates the results of hemogram, blood gas analysis, and coagulation.
Haemolysed samples
Haemolysis can occur due to excessive tourniquet application time, collecting blood with a syringe and introducing it with too much pressure when filling the tubes, centrifuging blood before complete coagulation, or refrigerating the serum tube before clot retraction. This problem increases the concentrations of several magnitudes, notably LDH, ALT, AST, CK, and potassium.
Lipemic samples
Lipemia is the presence of turbidity in serum or plasma due to increased lipoprotein concentration, either because the patient did not follow the recommended fasting or due to metabolic diseases. Lipemia causes elevated results for analytes whose determinations are based on absorbance at the same wavelengths at which lipid particles also absorb light. For example, it can increase the measured concentration of albumin, calcium, and phosphate.
Icteric samples
Jaundice is an abnormal yellowish coloration due to an excess of bilirubin. Icteric plasma or serum can interfere with analytical results of albumin, cholesterol, triglycerides, glucose, and total proteins.
Samples with drug interferences
Some drugs can produce interferences in the measurement procedure of various analytes. For example, levodopa increases the concentration of creatinine, glucose, and transaminases. Oral contraceptives increase erythrocyte sedimentation rate, glucose, alkaline phosphatase, lipase, and triglycerides concentrations, and decrease cholesterol and protein concentrations. Therefore, it is important for the laboratory to have the patient's clinical information when necessary.