the role of pathology service

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WALEED RAHMATI

The role of the Pathology Service

The Pathology Service is crucial. It provides diagnostic services to family doctors and hospitals department. It is varied discipline, ranging from the study of biochemicals, body tissues and bodily fluids to microbes and antibiotics. The media has given the subject a high profile, which reflects increasing public interest in the area of Pathology within forensics and criminology.      

I will study:

        

  • The role of the Biochemistry, Haematology, Microbiology, Pathology departments and type of tests undertaken in each department.

  • The stages involved in the processing of specimens and the importance of Health and Safety principles.

  • The knowledge and skills required by people working in the Biochemistry and Microbiology departments.

  • And how to conduct a Microbiological analysis and either a Chromatographic or Electrophoresis analysis.  

My Report will include:

  • The role of the Biochemistry Department

  • The types of specimens tested

  • The nature of the work undertaken in the department, including the common types of tests performed

  • For example testing for sugars in blood and urine

  • And estimating blood cholesterol

  • The principles involved in the use of either thin layer Chromatography or Electrophoresis analysis

The role of the Biochemistry Department

Introduction

The role of the Biochemistry department is to provide analytical chemical tests which help in the diagnosis in patients, and where appropriate to act as an advisory service to support treatment of patients.  

It undertakes the measurement of significant biological chemicals in the body. The sugar analysis in diabetes, cholesterol and amino acids detection are examples of its work.

The main role of the Biochemistry department is the analysis of the biochemicals, for example, hormones, minerals, vitamins, metabolites and enzymes.

Some are the common hormones which are diagnose are e.g. growth hormones, thyroxine.

  • Minerals, e.g. iron or calcium.

  • Vitamins, e.g. B, C, D and E.

  • Metabolites, e.g. cholesterol, glucose.

  • Enzymes, e.g. alkaline phosphate

Testing blood for the presence/ level of the hormone Thyroxine

Hypothyroidism

Hypothyroidism (underactive thyroid gland, myxoedema) is a condition in which the thyroid gland produces too little thyroid hormone (thyroxine) which results in effects on the whole body.

Symptoms

The thyroid gland, which is in the front of the neck, controls the rate of at which the body's cells work (the metabolic rate). Many people with a mildly underactive thyroid gland will not notice any symptoms. In hypothyroidism, the rate of metabolism is decreased, and this results in most of the symptoms:

  • feeling sluggish and tired
  • tendency to feel cold
  • weight gain
  •  
  • dry skin and hair
  •  
  •  

Causes

Hypothyroidism is more common than . In most cases it is because the thyroid cells begin to fail, and thus less thyroid hormone (thyroxine) is produced. This may occur without obvious cause, but may follow:

  • the body developing an immune reaction against itself (an auto-immune reaction) which destroys the thyroxine producing cells
  • an operation to remove part of the thyroid gland (usually for ), often years earlier
  • radioactive iodine treatment for  
  •  in earlier life
  • treatment with drugs you may be taking e.g. lithium, amiodarone

Very rarely hypothyroidism may follow failure of the production of the hormone (thyroid stimulating hormone, TSH) that is produced by a gland hanging from the underside of the brain (pituitary gland) to drive the thyroid gland. This is known as secondary hypothyroidism.

Diagnosis

In the presence of symptoms such as some or all of those above, the doctor is likely to arrange for a blood test to check on the amount of thyroid hormone (thyroxine) and other tests, looking at other hormones which control or are produced by the thyroid gland. These tests are collectively known as thyroid function tests. You may also have tests done to look for antibodies to thyroid (auto-antibodies).

In hypothyroidism the level of TSH (thyroid stimulating hormone) is usually elevated, and the level of thyroxine is low.

Treatment

The doctor is likely to prescribe thyroxine to patients (also known as levothyroxine or T4). In some cases it may be prescribed an alternative thyroid hormone, tri-iodothyronine (T3 or lyothyronine).

If patients are elderly or have any history suggestive of heart problems (eg  or heart failure), the doctor will start you on a lower dose, as thyroxine treatment increases the rate of work of all the cells in the body. Our system has probably been used to functioning at a lower rate for some time, and the increase in energy will cause extra work for the heart. It would be harmful to continue without treating an underactive thyroid gland, but, as with starting an exercise programme, it is sensible to build up to a higher level of metabolic rate in stages.

        

Follow up        

The way in which treatment with thyroxine is monitored is by visits to the doctor when he might ask questions about how you feel, check your weight and pulse, and sometimes check your reflexes (which relax slowly in hypothyroidism).

The main part of follow up, however, is regular checking of the level of TSH (thyroid stimulating hormone) in your blood. If the TSH level is high this means that you are not having adequate thyroxine to allow for your underactive thyroid gland. In this case the pituitary gland works harder, producing more TSH, in an unsuccessful attempt to make the thyroid produce more thyroxine. If the TSH level is normal then you are having adequate thyroxine to replace the lacking hormone from your thyroid gland (replacement therapy).

Initially you will have TSH blood tests every few weeks or months. If the TSH is high your doctor is likely to increase the dose of thyroxine. Most people do not need a dose of more than 150 micrograms of thyroxine per day.

Types of specimens tested

Types of specimens tested in the Biochemistry department include:

  • Blood
  • Urine
  • Cerebrospinal Fluid (CFS)
  • Sputum
  • Saliva
  • Faeces

I will write about each of them in my report.

Testing blood for the level of the mineral iron

Iron – haemoglobin – RBC

Iron is needed to make haemoglobin and is needed to carry oxygen. Iron can be determined indirectly by looking at.

The Packed cell volume (PCV) or haematocrit is the percentage of the total blood volume occupied by red blood cells. Traditionally this has been determine by centrifuging blood in a microhaematocrit tube and measuring the height of the red cell column, but now automated analysers are used to calculate PCV.

Centrifuging causes the components of the blood to separate. Red cells move to the bottom of the tube and plasma to the top, with a ‘‘Buffy coat’’ (which contains leucocytes and platelets) in the middle. The appearance of the centrifuged sample can also provide subjective information about the patient’s health.  

PCV can be used as a screening tool for anaemia and to indicate the degree of fluid loss in dehydration. A drop in PCV can also indicate internal haemorrhage before any other symptoms become apparent. PCV is raised in polycythaemia and in chronic hypoxia associated with pulmonary disease and congenital heart disease.

Mean cell volume (MCV) is the average volume of a red blood cell, measured in femtolitres. A raised MCV suggests folate or vitamin B12 deficiency, myxoedema, alcoholism or liver disease, haemolysis or aplasia. A reduced MCV suggests chronic blood loss, iron deficiency anaemia, thalassaemia or sideroblastic anaemia.    

Haemoglobin and cell haemoglobin concentration

 About a third of each erythrocyte is haemoglobin. One way of measuring haemoglobin concentration is to add a lysing agent to a sample of diluted blood so that the red cells release their haemoglobin. This can be converted to cyanomethaemoglobin and a spectrophotometer can then be used to measure optical density, from which haemoglobin concentration can be calculated.

Smoking can raise haemoglobin measures due to increased carboxy – haemoglobin. The mean cell haemoglobin concentration (MCHC) is a measure of the average concentration of haemoglobin in red cells. A reduced MCHC suggests iron deficiency or chronic blood loss.    

Ferritin and folate

About 30 percent of the iron in the body is stored as ferritin in the bone marrow, spleen and liver. The amount of ferritin in serum is directly proportional to the amount of iron in the body.

Serum ferritin levels are, therefore measured to diagnose iron deficiency anaemia. The usual range is 24-300ng/L for men and 15-300ng/L for women. Low serum ferritin levels are seen in patients with iron deficiency and in women who suffer heavy menstrual bleeds. Increased serum ferritin levels are seen in hyperthyroidism, Hodgkin’s lymphoma and breast cancer.

Another set often requested is serum folate or (vitamin B12). Usual levels range between 2 and 10ng/ml. folate levels are used to indicate pernicious anaemia or intestinal malabsorption disorders (e.g. Crohn’s disease), but decreased levels are also seen in people with chronic alcoholism. Suspected impaired B12 absorption can be investigated using the Schilling test. This involves giving the patient radioactive vitamin B12 and collecting urine samples over a number of days.    

        

Measuring Cholesterol levels

Introduction

Cholesterol is a STEROL present in most body tissues. It is an essential component of the body and plays an important role in many cellular functions. Cholesterol is obtained from the diet and is also synthesised in the liver. The first-line organ in cholesterol metabolism is the gut. The body absorbs 40-50% of cholesterol and makes 50-60% of cholesterol in the liver). However, cholesterol synthesised in the liver is derived from saturated fat and therefore is related to the amount of saturated fat eaten.

There are various enzymes responsible for the synthesis of cholesterol in the liver, the most important of which is HMGCoA (3-hydroxy-3 methylglutarylcoenzyme A) reductase. This enzyme helps to control whether cholesterol is secreted as bile salts or transported into the circulatory system. Daily cholesterol intake is about 300mg, most of which comes from animal-based food products such as red meat, poultry, fish, egg yolks and whole-milk dairy products. Although cholesterol absorption depends partially on the baseline diet, there are people who are hyperabsorbers and others who are hypoabsorbers.

The importance of checking cholesterol

Diseases of the heart and circulatory system are the main cause of death in the UK accounting for just under 238,000 deaths in 2002 (British Heart

Foundation (BHF) 2004). More than one in three people (39%) die from cardiovascular disease (CVD). The main forms of CVD include coronary heart disease (CHD) and stroke. CHD is the most common cause of death in the UK with more than one in five men and one in six women dying from the disease (BHF 2004).

In 2002, CHD caused more than 117,000 deaths in the UK. A raised cholesterol level is one of the risk factors for CVD. Other contributors to the disease include: hypertension, smoking, family history of CVD and diabetes. The risk of CHD is related to blood cholesterol levels. Research from the World Health Organization (WHO 2002) highlighted the importance of raised blood cholesterol as a risk factor for CHD. Cholesterol levels should be closely monitored and controlled where possible to reduce the growing burden of arterial associated disease in the UK.        

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The mean cholesterol level for men over the age of 16 years in England is 5.5mmol/l and 5.6mmol/l for women. Approximately 66% of men and 67% of women have cholesterol levels of 5.0mmol/l or more.

        

Genetic causes of raised cholesterol

There are a few genetic causes of raised cholesterol including familial hypercholesterolemia (FH), which is caused by an autosomal dominantly inherited deficiency of LDL receptors on cell surfaces

Medical conditions that may affect cholesterol testing

        

There are several medical conditions which can alter cholesterol levels from normal. This should be taken ...

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