Precautions in the Venipuncture Procedure

Venipuncture is a procedure that involves the extraction of blood from a vein making use of a syringe and a needle. This is done when the doctor wants to determine the levels of certain substances in blood to arrive at a correct diganosis.

It is an invasive procedure but the pain is tolerable when done by an expert. The most common site of puncture is the ante-cubital fossa which is composed of three veins, the cubital, basilic and the median cephalic. Blood extraction could be performed in veins that meet the criteria.

Here are some precautions to remember when performing venipuncture:

1. Be sure to identify the patient correctly. The reliability of results does not only concern the performance of the test but all processes involved with the test. This starts with patient identification. Ask the patient to state his name or to write it down. Make sure you got all your data entries correct including the complete name of the patient. There are people who have similar names so obtaining the middle name would be useful to solve such problems.

2. Know the tests required before commencing with the venipuncture as this would determine the type of blood specimen to collect and the manner of collection. i.e. anaerobic, for blood gas analysis (BGA), etc.

3. The site to be punctured should be free from hematoma and edema.

4. Proper sterilization procedures should be done before puncturing the vein, preferably a circular motion starting from the site of puncture going outwards. This is to minimize contamination of the site of puncture.

5. Do not puncture in the same vein that an IV fluid is inserted as the components of the IV fluid would contaminate your specimen. If you don't have any alternative, then collect your sample below the IV fluid.

6. Check that your syringe is not clogged by pulling and pushing the plunger. If it operates smoothly, then it could be used. Check also your needle of any factory defect. Do not; however, open the pack, not until you're ready to puncture as this may lead to contamination.

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Most Common Tests for Glucose

Glucose- also known as dextrose- is the most predominant carbohydrate. The glucose level in the blood is affected by diet through the food that we eat like carbohydrates (rice, bread, starch, etc.)

Blood glucose levels are usually tested in fasting samples of patients- Fasting Blood Sugar (FBS). The patient is required to fast for 8-12 hours before blood is extracted for testing. On certain occasions, Random Blood Sugar (RBS) or non-fasting samples are required too.

Oral Glucose Tolerance is also done in borderline suspected Diabetes Mellitus (DM) patients; sometimes an HbA1C test is done to monitor compliance to medication of patients.

Although automated procedures employing the enzymatic principle of glucose assays are now being adapted by many clinical laboratories, the manual method using the Orthotoluidine method is still useful. Some manual methods employ the oxidation-reduction property of glucose to measure its concentration.

In the Orthotoluidine method utilizes the principle of the condensation of aromatic amines by glucose to form a green end product which is then measured spectrophotometrically.

Unhemolyzed, non-icteric, non- tubid and non- lipemic serum is the best specimen. Serum is the supernatant fluid when coagulated blood is centrifuged. If an anticoagulant is used EDTA (ethylenediaminetetraacetic acid) is preferable.

The specimen and the orthotoluidine reagent is mixed and then boiled for 5-8 minutes, and then the absorbance or transmittance is read in the spectrophotometer. The reading will then be computed based on the absorbance /transmittance of unknown and standard and computed.

This formula is used to determine Cu (concentration of unknown):

Cu= Absorbance of Unknown/ Absorbance of Standard X Concentration of standard (Cu=Au/As X Cs)

This will give you the concentration in milligrams per deciliter. To convert this to mmol/L multiply it with 0.0555 (conversion factor)

The oral glucose tolerance test (OGTT) on the other hand, measures the body's ability to metabolize glucose. This test is used to diagnose borderline diabetes and also determines gestational diabetes mellitus (GDM) in pregnant women.

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