Abkhazia Institute for Social and Economic Research

To prevent hemolysis (which can interfere with many tests):
Mix tubes with anticoagulant additives gently 5-10 times
Avoid drawing blood from a hematoma
Avoid drawing the plunger back too forcefully, if using a needle and syringe, and avoid frothing of the sample
Make sure the venipucnture site is dry
Avoid a probing, traumatic venipuncture
Indwelling Lines or Catheters:
Potential source of test error
Most lines are flushed with a solution of heparin to reduce the risk of thrombosis                
Discard a sample at least three times the volume of the line before a specimen is obtained for analysis
Hemoconcentration:
An increased concentration of larger molecules and formed elements in the blood may be due to several factors:
Prolonged tourniquet application (no more than 2 minutes)
Massaging, squeezing, or probing a site
Long-term IV therapy
Sclerosed or occluded veins
Prolonged Tourniquet Application:
Primary effect is hemoconcentration of non-filterable elements (i.e. proteins). The hydrostatic pressure causes some water and filterable elements to leave the extracellular space.
Significant increases can be found in total protein, aspartate aminotransferase (AST), total lipids, cholesterol, iron
Affects packed cell volume and other cellular elements
Patient Preparation Factors:
Therapeutic Drug Monitoring: different pharmacologic agents have patterns of administration, body distribution, metabolism, and elimination that affect the drug concentration as measured in the blood. Many drugs will have "peak" and "trough" levels that vary according to dosage levels and intervals. Check for timing instructions for drawing the appropriate samples.
Effects of Exercise: Muscular activity has both transient and longer lasting effects. The creatine kinase (CK), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and platelet count may increase.
Stress: May cause transient elevation in white blood cells (WBC's) and elevated adrenal hormone values (cortisol and catecholamines). Anxiety that results in hyperventilation may cause acid-base imbalances, and increased lactate.
Diurnal Rhythms:
Diurnal rhythms are body fluid and analyte fluctuations
during the day. For example, serum cortisol levels are
highest in early morning but are decreased in the afternoon. Serum iron levels tend to drop during the day. You must check the timing of these variations for the
desired collection point.
Posture: Postural changes (supine to sitting etc.) are known to vary lab results of some analytes. Certain larger molecules are not filterable into the tissue, therefore they are more concentrated in the blood. Enzymes, proteins, lipids, iron, and calcium are significantly increased with changes in position.
Other Factors: Age, gender, and pregnancy