Laboratory:- Part 2 – Common Lab Errors, Effect of various Anticoagulants on Tests

- The handling of the specimens is critical to decreasing the error in the lab results.
There are the following areas where the mistake can lead to erroneous laboratory results:
- Specimen collection:
- Wrong techniques of blood collection like too much pressure on the blood collection area.
- Blood is put into the wrong test tubes for serum blood put into the test tube containing anticoagulant.
- The blood sample was wrongly labeled.
- Patients preparation:
- Blood was collected at the wrong time.
- If a blood sample needed a fasting sample and collected at a random time.
- There is a diurnal variation in the various blood samples. You may collect a sample at the peak level.
- Specimen handling:
- If the blood sample is delayed for the transfer to the lab.
- A blood sample is stored at the wrong temperature.
- did not properly process the blood sample.
- Chemical analysis:
- They are not following quality control rules.
- They are not following the protocol of the test procedure.
- There will be a difference in manual and automation.
- Reporting of the result:
- Mistakes in the calculation of the result.
- The difference in reporting the result on phone and on paper.
Indications for ordering laboratory tests:
- To confirm a clinical impression or to make a diagnosis.
- To rule out diagnosis or disease.
- To follow for the prognosis of the disease.
- To help in the therapy of various diseases.
- For the screening of the disease in the population.
The most common error in the collection of the samples and reporting are:
- Wrong labeling of the sample.
- The technique of the blood sample:
- This is very important to follow an excellent technique to collect good quality blood.
- If you apply tourniquet for a longer time, that will lead to acidosis and hemoconcentration.
- The wrong sample of the different patients or not the proper identification of the patient.
- The wrong ratio of the blood and the anticoagulant.
- Not proper mixing of the blood, and that may lead to the micro-clots formation.
- Keeping the sample at an extreme (hot) temperature.
- There may be hemolysis, which is not a good sample for electrolytes and so many other tests.
- Try to collect an adequate blood sample and avoid microclots.
- If there is a lipemic serum which will interfere with biochemical reactions.
- Wrong timing of the sample for some special tests like hormones etc.
- If a blood sample is taken after the food ingestion, then:
- The glucose level will be high.
- Will raise triglyceride.
- will rais lipid fractions.
- If a blood sample is taken after the food ingestion, then:
- Improper centrifugation of the blood which will not give a good clear serum.
- If the sample is not stored at the appropriate temperature.
- Some tests are influenced by the light to the blood, like bilirubin.
- The delayed performance of the tests.
- Human errors can also account for the laboratory variation. This depends upon the performance of testing.
- This can be minimized by automation.
- There will be mistakes if:
- Selecting a specimen to analyze from the wrong patient.
- There are transcriptional errors.
- There are any mistakes along the whole chain of collecting, processing, analyzing, and reporting.
The sample should be rejected when it is found:
- The sample shows hemolysis.
- The serum shows lipemia.
- When there are micro-clots in the blood sample.
- When the sample is too small to perform the test.
- When too much force applied to draw the blood.
- If the specimen is contaminated.
- If the container is leaking.
- Faulty transportation like very hot or cold weather.
- Unlabelled sample.
Effects of various anticoagulants on different tests:
Anticoagulants
|
Inhibit the value |
Decrease the value | Increase the value |
Stimulatory effect | Distort the morphology |
Oxalate
|
Inhibit | Decrease | Increase | Stimulate | Distort |
Alkaline phosphatase | Calcium | Sodium | —- | Blood cells | |
Acid phosphatase | —- | Potassium | —- | — | |
LDH | —- | —- | —- | — | |
Amylase | — | —- | — | — | |
Citrate
|
SGPT | Amylase | Sodium | Acid phosphatase | — |
SGOT | Calcium | Potassium | —- | — | |
Alkaline phosphatase | —- | —- | —- | — | |
EDTA
|
Creatine Kinase | Calcium | PT | —- | — |
Alkaline phosphatase | Iron | PTT | —- | — | |
platelet aggregation | Sodium | —- | — | ||
— | Potassium | —- | — | ||
Heparin |
— | T 3 | —- | — | |
— | Thyroxine | —- | — | ||
— | PT and PTT | —- | — | ||
— | Lithium | —- | — | ||
— | Sodium | —- | — | ||
Fluoride |
Acid phosphatase | — | Cell morphology | ||
Alkaline phosphatase | — | ||||
SGPT | — | ||||
SGOT | — | ||||
Creatine kinase | — | ||||
Amylase |
Precaution before performing the test:
- This is best to perform all the tests within the first 45 minutes to one hour after collection.
- If delayed then correctly store the sample at the appropriate temperature.
- The serum is needed for electrophoresis.
- For gases and ammonia, whole blood is needed.
- For clinical chemistry, the serum is the best option, but plasma may be used.
- For plasma preparation, centrifuge the blood within one hour of sample collection for 10 minutes at 850 to 1000 x gravity.
- Cap the bottle to avoid evaporation.