The haemagglutination inhibition test This, and the subsequent tests to be mentioned, are known as immunological tests. They are based upon the e?ect of the urine from a pregnant woman upon the interaction of red blood cells, which have been sensitised to human gonadotrophin, and anti-gonadotrophin serum. They have the great practical advantage of being performed in a test-tube or even on a slide. Because of their ease and speed of performance, a result can be obtained in two hours.
Enzyme-linked immunosorbent assay (ELISA) This is the basis of many of the pregnancy-testing kits obtainable from pharmacies. It is a highly sensitive antibody test and can detect very low concentrations of human chorionic gonadotrophin. Positive results show up as early as ten days after fertilisation – namely, four days before the ?rst missed period.
Ultrasound The fetal sac can be detected by ULTRASOUND from ?ve weeks, and a fetal echo at around six or seven weeks (see also PRENATAL SCREENING OR DIAGNOSIS).... pregnancy tests
Static lung volumes and capacities can be measured: these include vital capacity – the maximum volume of air that can be exhaled slowly and completely after a maximum deep breath; forced vital capacity is a similar manoeuvre using maximal forceful exhalation and can be measured along with expiratory ?ow rates using simple spirometry; total lung capacity is the total volume of air in the chest after a deep breath in; functional residual capacity is the volume of air in the lungs at the end of a normal expiration, with all respiratory muscles relaxed.
Dynamic lung volumes and ?ow rates re?ect the state of the airways. The forced expiratory volume (FEV) is the amount of air forcefully exhaled during the ?rst second after a full breath – it normally accounts for over 75 per cent of the vital capacity. Maximal voluntary ventilation is calculated by asking the patient to breathe as deeply and quickly as possible for 12 seconds; this test can be used to check the internal consistency of other tests and the extent of co-operation by the patient, important when assessing possible neuromuscular weakness affecting respiration. There are several other more sophisticated tests which may not be necessary when assessing most patients. Measurement of arterial blood gases is also an important part of any assessment of lung function.... pulmonary function tests
in septicaemia. Microbiology also looks for antibodies in the blood, which may confirm immunity to an infection. blood transfusion The infusion of large volumes of blood or blood products directly into the bloodstream to remedy severe blood loss or to correct chronic anaemia. In an exchange transfusion, nearly all of the recipient’s blood is replaced by donor blood. Before a transfusion, a sample of the recipient’s blood is taken to identify the blood groups, and it is matched with suitable donor blood. The donor blood is transfused into an arm vein through a plastic cannula. Usually, each unit (about 500 ml) of blood is given over 1–4 hours; in an emergency, 500 ml may be given in a couple of minutes. The blood pressure, temperature, and pulse are monitored during the procedure.
If mismatched blood is accidentally introduced into the circulation, antibodies in the recipient’s blood may cause donor cells to burst, leading to shock or kidney failure. Less severe reactions can produce fever, chills, or a rash. Reactions can also occur as a result of an allergy to transfused blood components. All
blood used for transfusion is carefully screened for a number of infectious agents, including HIV (the AIDS virus) and hepatitis B and hepatitis C.
In elderly or severely anaemic patients, transfusion can overload the circulation, leading to heart failure.
In patients with chronic anaemia who need regular transfusion over many years, excess iron may accumulate (haemosiderosis) and damage organs such as the heart, liver, and pancreas.
Treatment with desferrioxamine to remove excess iron may be needed.... blood tests
Urinalysis is a simple test in which a urine sample is examined under a microscope for blood cells, pus cells, and casts (cells and mucous material that accumulate in the tubules of the kidneys and pass into the urine).
Urine may be tested for substances, such as proteins, that leak into the urine when the kidneys are damaged.
Kidney function can be assessed by measuring the concentration in the blood of substances, such as urea and creatinine, that the kidneys normally excrete.
Kidney function may also be assessed by kidney imaging techniques.... kidney function tests
An audiometer (an electrical instrument) is used to test an individual’s ability to hear sounds at different frequencies and volumes. The lowest level at which a person can hear and repeat words (the speech reception threshold) is tested, as is the ability to hear words clearly (speech discrimination). The type of hearing loss (see deafness) is determined by holding a tuning fork to different parts of the ear.... hearing tests
In most intelligence tests, scoring is based on mental age (MA) in relation to chronological age (CA). The intelligence quotient (IQ) is MA divided by CA, multiplied by 100. The tests are devised to ensure that 3 in 4 people have an IQ between 80 and 120. They are standardized so that the score indicates the same relative ability at different age levels.
Intelligence tests may be used to assess school or job aptitude. However, they have been criticized for their alleged bias regarding gender and race.... intelligence tests
The tests can also show whether liver cells are healthy or being damaged.... liver function tests
Patch tests are used in the diagnosis of contact allergic dermatitis.
They can also be used to test immunity to certain infectious diseases (such as in the tuberculin test).... skin tests
The accuracy of a test is based on its sensitivity (ability to correctly identify diseased subjects), specificity (ability to correctly identify healthy subjects), and predictive value.
The predictive value is determined by a mathematical formula that involves the number of accurate test results and the total number of tests performed.
The best tests have both high specificity and high sensitivity, and therefore high predictive value.... tests, medical