Blood test

What is a blood test?

Blood test is one of the most used medical tests and one of the most important in clinical practice. It consists in the extraction of a small amount of venous blood from the patient, which is after transported to the laboratory for be analyzed and determine its composition.

Usually, the most solicited for study are complete blood count and blood biochemistry:

Complete blood count: is a quantitative study that evaluates the concentration of each blood's cell elements. It also checks if cells have a normal form or structure or on the contrary, they are altered.

Example: red blood cells, white blood cells and neutrophil.

Biochemistry: is the study of blood’s chemistry substances.

Example: potassium, calcium, sodium, magnesium, vitamins, hormones among others.  

How is the test made?

Generally, the blood’s extraction is made by a male or female nurse or a nursing assistant. The test usually lasts about 5 minutes.

1. During the blood´s extraction the patient will remain seated or lying down on a stretcher.

2. The patient will be asked to stay with the arms extended avoiding move them while the extraction will be made. 

3. The professional will look for an arm´s vain for puncture, generally a vein located on the anterior face of elbow´s flexion. He will put an elastic band immediately above the puncture point for help to vein’s filled and the posterior blood´s extraction.

4. The puncture zone is disinfected using sterile gauze soaked of alcohol.

5. For take the sample is used an hypodermic needle and a plastic syringe, both disposable. Generally a small part of blood´s sample is extracted, about 10 cc, although special studies can need a bigger sample.

6. After puncture, a sterile compress will be put over the puncture´s area and the patient will be asked to made a gentle pressure during some minutes until the puncture point does not have bleeding. 

Why can the doctor solicit a blood test?

Actually, a blood test is an exam that can be request form almost any medical consultation, with the objective of evaluate patient´s general condition. Simultaneously with his medical record, it will be useful to help the doctor to solve two important issues: what happens with the patient and why is happening.

An example: a person comes to the consultation with noticeable tiredness, loss of appetite and pallor; in this case, a simple blood test can reveal a diagnosis: Iron deficiency anemia.

Thus, the illness can be started to be treat without the necessity of implement more tests.

But there has to take into account that blood test is not just a method for illness diagnosis, it is also a way to control patient condition; for example, routine exams are made to sick people who receive chemotherapy for check their immune system; and before starting an hormonal treatment with oral contraceptives, is also important know patient´s level of hormones in blood.

Recommendations and preparation for the blood test

  Wear comfortable clothes

There is recommend the use of comfortable clothes, because after the extraction the patient most press the puncture point during 5-10 minutes for avoid hematomas and bleeding.

 The most important when you will realize a blood test is go on a fast, for avoid the presence of factors that can produce mistakes in the results. Normally, the blood´s extraction is done in the morning, because this patient most fast since 12 of night (it usually correspond to a period of 8-10 hours).

 Drink water in a moderated form 

Normally patients go to the extraction without drink water during more than 8 hours. However, specialist guarantee that water can be drunk in a moderate form, except when doctor prohibit it specifically.

 On the contrary that people use to think, the dehydration difficult blood´s extraction. If we drink water in a moderate form veins are expanded and they are more visible. 

  Moreover the mention before exist other norms to fallow before a blood test, such as avoid realize physical exorcise the previous day, consume alcoholic drinks or tobacco.  

 These are general norms for the most habitual blood´s extraction, in spite of there are exams that will request other preparation. In these cases, the doctor or the same clinical laboratory will informer you about the steps to follow for have optimum results.

Risk of the study

It is a test that does not cause to much pain for almost all people, although some of them can feel discomfort or a little pain when they are puncture or during the extraction of blood. In some occasions the patient can feel sick or even loss the conscience because the fear to the test or the prolonged fast, but in any of these cases this incident is due to the extraction itself, because the quantity of blood that is taken is very small.

 In any case, if the person is prone to dizziness, is recommendable go accompanied to the test.

  Risks are minimum and easily treatable by your doctor:

•Discomfort in puncture point.

•A little bleeding in patients with coagulation problems.

•Hematoma in puncture area. 

•Phlebitis (inflammation/infection of the utilized vein during the puncture).

The patient most consult with his doctor before realize the test in case that he consumes or uses anticoagulants.

As more notable adverse effects to the analytic realization, it can remain a little hematoma o swelling in the extraction area. This is because the blood of the vein goes out for the place where it has been puncture. The hematoma disappear a few days after without the necessity of treatment.

 The only contraindication for the blood test's realization is the ingestion of anticoagulants. These medications could cause more bleeding than normal, or very extensive hematomas.

How interpret blood test´s results? 

Patient should not worry about a separate decrease or elevation of some mentioned parameter, because is the doctor who must evaluate the meaning of the results, inside medical record´s context, and in relation with other symptoms and personal patient circumstances (life style, presence of other pathologies, medication that patient is taken).