diagnosis is derived from the Greek word ‘gnosis’ which means knowledge. It basically refers to determining if
a disease or disorder exists and to define its nature. It involves analysis of data on symptoms, signs, and specific investigations.
Background knowledge of disease epidemiology and disease risk factors in an area at a given point in time helps in arriving
at a correct diagnosis.
1.2 Probability in diagnosis
not be possible to reach conclusion about one diagnosis and one may have to identify several diagnoses and arrange them in
order of likelihood. Therapeutic interventions are undertaken on the basis of a leading diagnosis and alternate diagnoses.
The legal basis for intervention in such cases is ghalabat al dhann or predominant
conjecture. Further manifestations of the disease process or response to therapy may finally allow definitive determination
of the diagnosis. There are situations in which the final diagnosis cannot be determined until after death when post-mortem
examination reveals the true cause of death.
1.3 Basis of diagnosis
diagnosis relied more on symptoms. With development of systematic methods of clinical examination more reliance was placed
on signs. However major breakthroughs in diagnosis were achieved when medical technology provided a wide array of accurate
and reliable laboratory and radiological investigations. Instruments were also developed to be able to make more accurate
observation of signs both inside and outside the body. Further refinements in diagnosis are going to be based on technological
developments but will never supplant the role of careful history taking for symptoms and clinical examination for signs.
1.4 Use of computers
are being used increasingly in the diagnostic process to process and summarize massive volume of quantitative data and compute
probabilities of various diagnostic possibilities. The human mind is still needed to make the final diagnosis because the
computer in the end is a machine and does not fully encompass all the creative and innovative thinking skills found in a human
physician. Physicians acquire diagnostic competence through long periods of practical clinical training because in the end
medicine is an art. Computers and other machines cannot have this clinical competence.
a diagnosis requires summarizing and analyzing information collected from history, physical examination, and various investigations.
The clinician initially develops a series of possible alternative diagnoses called the differential diagnosis. With use of
further information from investigations or sometimes response to therapy, the diagnostic possibilities are narrowed down even
further. Sometimes a diagnosis is arrived at by elimination. Computers using algorithms developed by experienced clinicians
can be used to aid the diagnostic process.
2.0 CLINICAL HISTORY
The purpose of history taking is to discover the social or personal antecedents of disease as well as the natural history
of the disease. This involves considerable probing into personal life and privacy. It provides a golden opportunity for both
physician and patient to face diseases of the heart, amraadh al qalb, that affect
physical health. The diseases of the heart may be transgression, dhulm; neglect,
ghaflat; loss of self-control and following passions (sex, drug, and alcohol-addiction).
There is an opportunity for the physician to exercise the function of da’wah and for the patient to make repentance,
2.3 Legal issues
History taking is also an opportunity for discovery of legal complications such as foster relations that prohibit marriage,
defective marriages concluded during ‘iddat. In complicated medical conditions,
history taking may be an opportunity for discussing costs of medical care with the patient. The physician taking history may
face a major ethical dilemma when in the course of taking history, the patient volunteers information about a criminal action
that should be prosecuted. If the physician keeps the information to himself, he is not fulfilling the duty required of him
as a citizen to report crime to the authorities.
2.4 Communication skills
Successful history taking requires good communication skills and careful observation of non-verbal clues. Accurate
history depends on the honesty and memory of the patient. Patients may not want to reveal some information that they consider
embarrassing or that they mistakenly consider irrelevant to the presenting disease condition. Patients may forget some information
or confuse it. The interviewer must be tactful and sensitive in probing for relevant information and may have to adopt various
strategies to help the patient’s memory. Questions may be open-ended or closed. Sometimes the interviewer may just have
to keep quiet and listen actively as the patient talks to be able to pick up useful clues. Interrupting patients is a frequent
problem of interviewers who pressed for time would like to keep the interview as short as possible. Patients with underlying
emotional problems may only verbalize physical symptoms and it requires tact and establishment of rapport to get them to talk
about their inner worries and feelings.
2.5 Elements of a medical history
A complete medical history consists of an account of the present illness and its evolution since first noticed, relevant
past medical history, family history, social history, psychological history, and history of occupational and environmental
Account of the presenting illness covers recent changes in health status, associated triggering factors,
and all changes that have occurred from the start until presentation to the physician. The account is not completed on the
first interview. In the course of clinical examination or treatment signs may be identified that suggest eliciting more information
about the causes and course of the presenting illness.
Past medical history covers health status and disease experiences as back as can be remembered. It includes medical,
surgical, and psychiatric conditions. Both severe illnesses requiring hospitalization and less severe ones treated symptomatically
or not treated at all need to be recorded if they have relevance to the presenting illness. The interviewer must have an extensive
knowledge of disease epidemiology and disease pathophysiology to known what relevant questions to ask.
Family history elicits information about diseases in immediate family members because the presenting illness may have
a familial hereditary basis or an environmental basis in the domicile of the patient.
Social history elicits information about social factors that are relevant to disease such as marital status, education,
lifestyle (eg alcohol, drugs, smoking), and beliefs.
Occupational and environmental exposures should be documented for a long time before the presenting illness because
for chronic diseases the causative agent may act years before the presenting illness.
History taking is completed by a thorough review of the organ systems. The patient is asked specific questions about
symptoms in each system that may have relevance to the presenting complaint.
3.0 CLINICAL STATE EXAMINATION
4.0 LABORATORY INVESTIGATIONS
The purposes of laboratory investigation are to provide base-line
information, establish a diagnosis, exclude alternative diagnoses, evaluate severity, plan treatment, and predict prognosis.
Results of laboratory tests are used in the process of decision making at all stages of clinical management. Usually treatment
is based a provisional diagnosis. The final or discharge diagnosis is confirmed towards the end of the disease episode. The
test must be sensitive and specific. Due to availability of automatic processing of biological samples physicians no longer
ask for specific tests but ask for a battery of tests. This risks producing false positive results on the basis of chance
alone. The range of normal results varies with the test technique and with age or race. The results of laboratory investigations
have the same requirements for confidentiality as history and clinical examination.
4.2 Types of investigations
Hematological investigations are carried out for anemia, hemoglobinopathies, bleeding disorders,
blood grouping, and blood compatibility. A complete blood count (CBC) consists of number of red blood cells, number of white
blood cells with a differential count, hemoglobin concentration, hematocrit, red cell volume (MCV), and platelet count. Coagulability
is assessed by the prothrombin test, the partial thromboplastin time, plasma fibrinogen, and blood clotting factors. The erythrocyte
sedimentation rate (ESR) is a non-specific indicator of inflammation. The Coombs or antiglobulin test (AGT) tests red blood
cell compatibility for purposes of transfusion.
Histopathological diagnosis describes the pathological process and indications of possible initial
Microbiological investigations are bacteriological, virological, and parasitological.
Biochemical investigations include renal function tests, liver function tests, fluids, electrolytes,
and acid-base balance. Fasting blood glucose level and the glucose tolerance test are used to diagnose diabetes mellitus.
Gastrointestinal absorption is assessed by measuring urinary excretion of ingested radioactive substances or urinary excretion
of D-xylose, a substance that is not metabolized by the body. Intestinal absorption can also be assessed by the amount of
fat in stool collected over 3 days following a fat-rich diet. Levels of various toxins are measured in serum or other body
fluids using specialized biochemical tests.
Immunological tests assess presence and concentration of antibodies.
Genetic/chromosomal analysis is used increasingly in disease diagnosis. Careful family history taking
and physical examination are used to construct a family pedigree for a specific disease. Among specific genetically-related
tests are: chromosome karyotyping, enzyme assays, hormonal assays, aminoacid assays, blood grouping and typing, immunoglobulin
assays, and hemoglobin electrophoresis. Prenatal tests for congenital genetic disease is controversial because it encourages
abortion. Genetic tests pose a special problem because genetic findings in a patient give information about genetic make-ups
of parents and siblings. Thus disclosure of the patient’s genetic findings may require in addition the consent of the
Biological markers are used in diagnosis and follow up of disease treatment the commonest being:
HCG for trophoblastic tumors & hepatocellular carcinoma; AFP, HCG, HBD, PLAP for germ cell tumors; CEA for GIT tumors,
CA125 for ovarian cancer; PSA for prostate cancer; CA and S-3 for breast cancer; and SCC for skin cancer. analysis is used increasingly in disease diagnosis.
Urine examination includes assessment for color, turbidity, cells, urinary casts, specific gravity,
bilirubin, urobilinogen, hemoglobin, glucose, ketone bodies, pH, protein, and bacteria.
Fecal examination consists of fecal occult blood testing (FOBT), culture for microorganisms, and
examination for parasites.
Cerebrospinal fluid is examined for white blood cells, culture for microorganisms, glucose, protein,
and fluid pressure. Gastric juice is examined for blood and is cultured for microorganisms.
Semen is examined for number, motility, and normality.
5.0 RADIOLOGICAL/IMAGING INVESTIGATIONS
5.1 Non-invasive investigations
Radiological investigations reveal a lot of information with minimal invasion. The commonest radiological examination
is the plain X-ray film. It may be enhanced by used of barium or air to show inside structures better. Computed tomography
(CT scan) produces a cross-section of the body at various levels. Ultrasonography
uses sound waves to define internal structures. It is quick and cheap but is not as accurate as CT scan or MRI. Magnetic resonance
imaging (MRI) uses magnetic fields and radiowaves to produce images of internal structures. It is more accurate than CT scan
but is more expensive and more cumbersome to use. CT can and MRI produce 2-dimensional images but newer techniques are able
to produce 3-dimensional images. Mammography is used to screen for breast cancer. The results of radiological investigations
are confidential. Images that show the shape of the body parts can be considered showing awrat and should not be seen except
by authorized people only and for specific purposes. Digital subtraction angiography and positron emission tomography are
5.2 Invasive investigations
The electrocardiogram (ECG)
assesses cardiac electrical conduction. The electroencephalogram (EEG) measures electrical activity in the brain. The echocardiogram
uses sound waves to assess structure and movement of the heart and is more useful in children. Myocardial perfusion imaging
uses radioactive thallium injected intravenously to study heart pathology detected by disturbance in radioactive uptake. Electromyography
assesses electrical conductivity in muscles.