In the case of venipuncture sample collection, the tourniquet application time should be a maximum of 2 minutes. Excessive prolongation can cause hemoconcentration and alter some analytes concentrations. For patients with therapeutic serums or catheters, it is recommended to collect the sample from the arm opposite to the infusion site. If the sample must be obtained through a catheter, it is recommended to discard the amount of blood equivalent to twice the volume of the catheter beforehand.
The laboratory must ensure that the collection and transport materials have the appropriate characteristics according to the type and volume of the sample. Therefore, all the materials used for each type of sample must be validated.
In the case of blood collection tubes, a specific order of tube filling is recommended to minimize the risk of contamination with the additives they contain. Contamination by anticoagulants should be avoided, knowing the compatibility of each type of sample tube with the analytes to be measured. For analyses on whole blood, a tube with anticoagulant must be used, and the sample must not be centrifuged. If blood is centrifuged in a tube with anticoagulant, plasma is obtained. The possible interferences of the anticoagulant used on the analytes to be measured must be considered. Serum is obtained by centrifuging the blood sample in a tube without anticoagulant.
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.