Blood sample which should be discarded, and Effect of Pressure While Collecting the Blood
- Whenever you find the following possibilities, reject the sample, and try to get another fresh sample.
Samples to be rejected are:
- Hemolyzed sample:
- Serum shows evidence of hemolysis when the hemoglobin is >20 G/dL.
- Slight hemolysis does not affect most of the test values.
- Severe hemolysis causes a dilutional effect of those constituents, which has a low concentration in the RBCs than the plasma.
- There will be a marked effect of those parameters present in high RBCs concentrations than in the plasma.
- Hemolysis will increase the value of:
- Lactate dehydrogenase (LDH).
- Total acid phosphatase.
- Lipemic serum:
- Serum with lipemic appearance will affect chemistry tests like:
- Total protein.
- ALT (Alanine aminotransferase).
- Ultracentrifugation can remove the effect of lipemia.
- The sample for CBC is unsuitable if there are clots and is hemolyzed.
- If there are microclots, are not suitable for Cell counting, it will give a low count.
- If there is an insufficient blood sample.
- If the sample is not labeled.
- If there is a discrepancy between the sample and the request form.
- If the blood sample is insufficient in quantity.
- Poor handling of the sample when there is the effect of light.
- Sample collected at the wrong time.
- If there is contamination of the sample.
Changes in the blood/serum when the vein is pressurized too much:
- Most of the time tourniquet is used to put pressure on the vein to make it prominent.
- When a blood pressure cuff is used, then mostly the pressure given is ∼60 mm Hg.
- Never leave the velcro pressure cuff for more than one minute, but it will give changes in the blood chemistry even with a shorter period of time.
If the cuff is applied for 1 to 3 minutes, it will lead to blood chemistry changes:
|Parameters||Increase in concentration||Decrease in concentration|
- The blood sample near the tourniquet has the same composition as the circulating blood.
- So use the first sample for the critical values like serum calcium.
- The first tube may show a 5% increase in the protein level, while the third tube shows a 10% change.
- In the case of slight trauma to the skin may increase the enzymes (SGOT).
- In the case of stress to the patient will increase in the growth hormone and cortisol.