Blood Tests – Why Are Blood Tests So Important?

The laboratory analysis of a blood sample is termed as the blood test. A blood test generally requires blood sample drawn from a vein in the arm. The need for such tests is to determine the biochemical status and the physiological condition in the patients suspected of diseases, mineral deficiency, organ malfunction and drug ineffectiveness. Most routine tests are performed on the serum or plasma, though the name still states ‘blood test’.

Types Of Blood Tests

Biochemical Analysis

  • The blood urea, nitrogen, calcium, chloride, creatinine, bicarbonate, magnesium, glucose, potassium and sodium are measured by the basic metabolic panel.
  • Some blood samples are also collected during fasting like in case of tests to measure glucose, cholesterol or to determine presence of STD.
  • You need to have your blood drawn 8-12 hours after fasting.
  • Mostly the blood is drawn from a vein in the arm, but some cases require the arterial blood gas test.
  • This requires the blood drawn from an artery.
  • The blood gas analysis requires arterial blood in order to determine the levels of carbon dioxide and oxygen.
  • The levels of bicarbonate and the blood pH is also measured using this test.

Table Showing the Normal Ranges

Tests Low High Unit Comments
Sodium (Na) 136 145 mmol/L
Potassium (K) 3.5 5.5 mmol/L
Urea 2.5 6.4 mmol/L BUN (Blood Urea Nitrogen)
Urea 7 18 mg/dL
Creatinine – male 62 115 I?mol/L
Creatinine – female 53 97 I?mol/L
Creatinine – male 0.7 1.3 mg/dL
Creatinine – female 0.6 1.1 mg/dL
Glucose (fasting) 3.9 5.8 mmol/L
Glucose (fasting) 70 105 mg/dL

Molecular Profiles

  • Protein electrophoresis,
  • Western blot,
  • Liver function tests
  • Polymerase chain reaction (PCR-DNA). The DNA can be taken out from a very small quantity of blood sample.
  • Northern blot (RNA)
  • Diagnosing Sexually transmitted diseases (STDs)

Cellular Evaluation

  • Complete / Full blood count
  • Hematocrit and MCV (mean corpuscular volume)
  • Erythrocyte sedimentation rate (ESR)
  • Cross-matching: Determining the type of the blood transfusion or transplants
  • Blood cultures are used when an infection is suspected.

Extraction Of The Blood Sample

The process of venipuncture is relatively non-invasive, hence is more useful to obtain the cells or their extracellular fluids. The blood is considered as the most common way to detect a body condition because:

  • Blood is responsible for carrying oxygen,
  • Blood helps in exchange of gases,
  • Blood carries the nutrients to all parts of the body,
  • Blood can dispose the waste products out by carrying them to the excretory system,

So most of the diseases or health conditions can be diagnosed using blood samples.

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