Study Guide:

With respect to skills:

Level 1 = should have confidence in performing the task and can recognize normal signs;

Level 2 = should have performed the task;

Level 3 = should have observed the task performed in real life or on video.

With respect to knowledge:

Level 1 = should understand the subject matter and can apply it to practice;

Level 2 = should have a sound understanding of the subject matter;

Level 3 = should be aware of the importance of the subject matter.

Medical History and Physical Examination versus Laboratory Tests

Three basic steps to making a diagnosis:

• Obtaining a medical history,

• Performing a physical examination of the patient,

• Sampling specimens from patient for laboratory investigation (e.g., chest x-ray, blood counts).

Many inexperienced doctors ignore the importance of history and physical examination in the believe that laboratory tests alone is the best method of arriving at a correct diagnosis. Let us examine the evidence:

• Consider a specific chest infection that affects 50 out of every 10,000 individuals in HK and this infection can be seen on the chest x-ray.

• All laboratory investigations, including x-ray, can yield false negative results (a negative result when there is disease). If the false negative rate of x-ray in this example is 2%, then 1 of the 50 patients who have the disease will have a falsely negative x-ray; and the other 49 patients who have the disease have a truly positive x-ray.

• Laboratory investigations can yield false positive results too (a positive result when there is no disease); if the false positive rate of x-ray in this example is also 2%, then out of the 9950 individuals who do not have the disease 199 (2% x 9950) will have a falsely positive x-ray.

• It can be seen from this example that using x-ray alone on 10,000 unselected individuals, the diagnosis is more often wrong than right (correct in 49 patient, falsely negative in 1 patient, falsely positive in 199).

• Now let us suppose fever is a feature of this chest infection and 10,000 individuals with fever (not just 10,000 random individuals) are selected for chest x-ray. More individuals out of this 10,000 with fever will be infected: say 500 out of 10,000.

• Out of these 500, 10 will have a falsely negative x-ray and 490 will have a truly positive x-ray.

• Out of the 9,500 individuals who have a fever but do not have the chest infection (they may have a fever because of some other infection), 190 will have a falsely positive x-ray.

• This shows that by using only one complaint, fever, to select individuals who should have a chest x-ray, the odds of a correct x-ray diagnosis has already improved to 490 being correct (truly positive) and 200 being incorrect (falsely negative in 10 and falsely positive in 190).

• Let us go one step further and suppose other features of this chest infection are weight loss, cough, bloody sputum, and wheezes; and 8,000 of 10,000 patients with all these complaints have the chest infection (the other 2,000 having other illnesses causing similar complaints).

• When the diagnostic x-ray is applied to these 10,000 who have all these complaints, 160 of the 8,000 infected patients will have a falsely negative x-ray but 7,840 will have a truly positive x-ray.

• Of the 2,000 who do not have this chest infection, 40 will have a falsely positive x-ray.

• By obtaining a good medical history and performing an appropriate physical examination, the ratio of correct to incorrect x-ray diagnosis is much improved (7,840 correct diagnosis, 160 falsely negative diagnosis, 40 falsely positive diagnosis).

What would happen to those patients who have a falsely negative chest x-ray? First of all, a conscientious doctor would not allow the negative chest x-ray result alone to overrule the many positive clinical findings. Secondly, the diagnosis may be confirmed by some other tests (e.g., sputum culture) or by a repeat chest x-ray. For 2 consecutive chest x-rays to be falsely negative in the same patient would be extremely rare.

Laboratory tests are expensive:

• Chest x-ray 150.00
• Complete blood count (picture) 100.00
• Renal function profile 132.00
• Liver function profile 165.00
• Magnetic Resonance Imaging (MRI) of knee 4000.00

Take home message:

The medical history and physical examination is the most valuable part of the clinical examination in reaching a diagnosis.

Inspection: the first step in physical examination

• Four basic techniques in physical examination: (1) Inspection, (2) Palpation, (3) Percussion, and (4) Auscultation.

• In recording your findings, it is important to comment on both positive findings as well as relevant negative findings.

• Inspection is the foremost diagnostic skill to be mastered in both Western and Chinese Medicine.

• The eyes is a doctor’s best diagnostic instrument: always available and requires little effort in its use.

• What is required is a heightened power of observation, which can be acquired through practice.

Just by general inspection, you can gain an idea of the following characteristics about your patient, all of which have health implications:

• Gender (some illnesses have a gender preponderance);

• Age or whether the patient looks older or younger than the stated age;

• Ethnic or geographic origin (some illnesses are more prevalent among certain ethnic groups);

• Occupation (e.g., white or blue collar worker);

• General nutrition state (emaciated, skinny, well nourished, fat, morbidly obese);

• Attention to hygiene;

• Patient’s habits (e.g., the habit of smoking is a risk factor of diseases of the cardiovascular and respiratory system);

• Patient’s mental status (alert, intoxicated, etc);

• Physical well-being (in distress or pain).

In addition to general inspection, specific inspection of body regions is also part of the physical examination of those regions. However, you must be on guard against the common human failing of forming pre-conceived ideas. Record your opinions honestly but be prepared to review them critically and revise them in the face of new findings. Do not fall into the trap of seeing “what you look for” and recognizing “only what you know”, a warning raised by the Bostonian Merril C. Sosman.

Exercise

• You will be given an opportunity to try out your power of observation during your session in the Clinical Skills Learning Center. You can practice this skill in your daily life too: Simply pick a person in your vicinity and note as much details about him or her as you can.

The stethoscope

• A stethoscope has 3 principle functions:
1. To exclude environmental noise from the room;  2. To transmit sounds from body parts of the patient to the ears of the examiner;  3. To emphasis sounds of certain frequencies selectively.
• A stethoscope has 2 earpieces joined by a Y-tubing to a chest piece.
• The earpieces fit into the external meati (external opening of the ears; meati is the plural of meatus) pointing downward and forward in the direction of the external ear canals. They should fit snugly to block out room noise; the spring must be strong enough to hold the earpieces in place without causing discomfort.
• The length of the tubing should be limited to 25 to 30 cm. A longer tubing may be more convenient but will dampen the sound transmitted. It should also be thick enough to exclude external noise.
• The chest piece is equipped with both a diaphragm and a bell.
• The diaphragm should be applied firmly to the chest wall; it is designed for picking up high-pitched (high frequency) sounds and filter out low pitched (low frequency) ones.
• The bell should be applied only lightly to the chest wall; it is more sensitive to low-pitched sounds. If the bell is pressed firmly against the chest wall, the underlying skin is stretched and the bell will function more like a diaphragm.
• Turn the chest piece to switch between bell and diaphragm function.
• Do not confuse the conventional stethoscope with the 3M Littmann Master Cardiology sthethoscope. The Master Cardiology stethoscope has only a diaphragm- like chest piece. It functions like a diaphragm when pressed lightly onto the body surface and like a bell when pressed firmly onto the body surface.
• Auscultation is best performed in a quiet room.
• Never auscultate without properly exposing the body part to be auscultated or through clothing. Clothing can muffle or add extraneous sounds.
• Do not put yourself at a disadvantage by buying a cheap stethoscope that is inefficient.

Exercise

1. Listen to your fellow student’s chest for heart and breath sounds using the different makes of stethoscope and decide for yourself which one you should buy.

2. Use the better scope and listen to your fellow student’s chest through clothing and through bare chest and decide for yourself which is better.