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Routine blood tests

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Haematology tests and maintaining urea and electrolyte balance

Haematology tests

These determine specific blood levels:

  • WBC4-11 (x109/l)
  • White cell differential (x109/l)
  • Neutrophils 2.5-7.5 (60-70%)
  • Lymphocytes 1.5-4.0 (25-30%)
  • Monocytes 0.2-0.8 (5-10%)
  • Eosinophils 0.04-0.44 (1-4%)
  • Basophils Up to 0.1 (up to 1%)
  • RBCMale: 4.5-5.5 x 1012/l Female: 4-5 x 1012/l
  • MCV80-99 (fl)
  • MCH27-33 (pg)
  • HbMale: 13.5-18g/dl Female: 11.5-16.5g/dl
  • HaematocritMale: 0.40-0.54ml Female 0.35-0.47ml
  • Platelets150-400 (x109/l)
  • ESRDepends on technique. Using Westergren method for males it is age (years) divided by 2; for females age + 10 divided by 2

They are useful in diagnosing such diseases as anaemia, leukaemia and infection.

White blood cell (WBC) count and differential

WBC count can be used to diagnose infection and inflammation, and to monitor response to chemotherapy or radiotherapy. White cell differential provides more specific information about the immune system. There are five major types of WBC: ϠNeutrophils; ϠLymphocytes; ϠMonocytes; ϠEosinophils; ϊBasophils.

Red blood cell (RBC) count

The RBC count helps to assess the blood’s oxygen capacity and diagnose anaemia, protein deficiency and dehydration.

Haemoglobin (Hb)

Haemoglobin transports oxygen. It is the main component of RBCs and a good indicator of anaemia.

Haematocrit or packed cell volume (PCV)

This reflects the proportion of blood occupied by RBCs by measuring the percentage of volume of packed RBCs.

Platelets

Platelets or thrombocytes promote coagulation by providing phospholipids to the intrinsic clotting pathway, helping to form a plug for vascular injuries.

Erythrocyte sedimentation rate (ESR)

The ESR measures the degree of erythrocyte (RBC) settling in a specified period. The ESR is sensitive but nonspecific, and is commonly the earliest indicator of disease when other chemical or physical signs are normal. Normal range depends on the technique used (e.g. Westergren, Wintrobe or Seditainer).

Common blood chemistry tests

Blood chemistry tests help evaluate respiratory and metabolic status. The following tests are covered: ϠUrea and electrolytes (sodium, potassium and creatinine); ϠLiver function tests (bilirubin, alkaline phosphatase, albumin, aspartate aminotransferase). Normal ranges are:

  • Urea3.5-8.8mmol/l
  • Sodium135-145mmol/l
  • Potassium3.5-5.0mmol/l
  • CreatinineMild renal impairment: 150-300µmol/l Moderate renal failure: 300-700µmol/l Severe renal failure: 700µmol/l
  • Bilirubin<18µmol/l; total bilirubin is 3-20µmol/l; indirect bilirubin is 0-14µmol/l
  • Alkaline phosphatase90-300IU/l depending on method of assay
  • Albumin30-55g/l
  • ASTMale: 8-46U/l; Female: 7-34U/l

Urea

Urea is a product of amino acid metabolism and is largely excreted by the kidneys.

Sodium (Na+)

Sodium affects water distribution, maintains osmotic pressure of extracellular fluid, promotes neuromuscular function and maintain acid-base balance and influences chloride and potassium levels.

Potassium (K+)

Potassium is the major intracellular cation.

Creatinine

Creatinine is a nitrogenous metabolic substance in muscle and blood and excreted in the urine. The serum creatinine test provides a sensitive measure of renal damage because renal impairment is virtually the only cause of creatinine elevation.

Bilirubin

This is the main pigment in bile and the major product of haemoglobin catabolism.

Alkaline phosphatase

This enzyme influences bone calcification and lipid and metabolite transport.

Albumin

Albumin is a major blood protein.

Aspartate aminotransferase (AST)

Essential for energy production, AST is found in the cytoplasm and mitochondria of many cells - primarily the liver, heart, skeletal muscle, pancreas and kidneys. OthersThis section includes:

  • Blood glucose and glycosylated Hb;
  • Cholesterol and lipids (very low and low-density lipoproteins, high-density lipoproteins)
  • Thyroid function (total serum and free serum thyroxine; total serum triiodothyronine; thyroid stimulating hormone)

Blood glucose

This is used to detect diabetes. Glucose is present in blood for basic fuel, and is stored in the liver and muscles as glycogen. It is derived from carbohydrates in the diet, but in conditions of shortage can be synthesised from fats or proteins.

Cholesterol

A steroid alcohol found in animal fats and oils, bile, blood, brain tissue, milk, egg yolk etc. High levels of total serum cholesterol are associated with a high risk for coronary artery disease.

Low-density lipoprotein

This carries cholesterol from the liver to the cells. If there is too much LDL in the blood, cholesterol may find its way into artery walls, where it begins to build up and cause atherosclerosis.

High-density lipoprotein

This returns excess cholesterol to the liver.

Total serum and free serum thyroxine;

Thyroxine influences a number of processes including metabolism of carbohydrates, fats, proteins, electrolytes and water.

Total serum triiodothyronine

An iodine-containing compound with several times the biological activity of thyroxine.

Thyroid stimulating hormone (TSH)

Secreted by the anterior pituitary, TSH stimulates an increase in the size, number and activity of thyroid cells, and release of iodthyronine (T3) and thyroxine (T4).

Normal ranges are:

  • Glucose4.5-5.6mmol/l

Diagnosis of diabetes mellitus:Symptoms (i.e polyuria, polydipsia and unexplained weight loss

PLUS:Random venous plasma glucose:11.1mmol/lORfasting plasma glucose:7.0mmol/lOR2-hour plasma glucose concentration:11.1 mmol/l, 2 hours after 75g anhydrous glucose in an oral glucose tolerance test.

  • Glycosated haemoglobin3.8-6.4%

Cholesterol and lipids

  • Total serum cholesterol 3.9-7.8nmol/l
  • Very low density lipoprotein 0.128-0.645nmol/l
  • Low density lipoprotein 0.128-0.645nmol/l
  • High density lipoprotein Male: 0.7-2.0nmol/l; female: 0.95-2.15nmol/l
  • Total lipids4.0-10g/l

Thyroid function

  • Total serum thyroxine 60-160nmol/l
  • Total serum triiodothyronine 1.2-3.1nmol/l
  • Free serum thyroxine 13-30pmol/l
  • TSH0.5-5.5mIU/l

 

References

McGee, M. (2000) A Guide to Laboratory Investigations (3rd edn).

 

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