“I’m sending you a copy of my blood tests. Please review them and tell me what supplements I should be taking.”

My heart sinks every time I receive that request, which is, unfortunately, quite often. While many people believe laboratory tests provide definitive answers about health, I rarely request them. In most instances, I do not find them valuable or necessary.

I attended medical school in an era that valued bedside diagnostic skills. I was taught that the most important part of any evaluation was the medical history – what the individual seeking my assistance was able to tell me. A good history, I was told, provides between 85 and 90 percent of all of the information available about a person’s medical condition.

A medical history begins with a chief complaint. What is the single most important health issue at this point in time? It may be as simple as “I want to be sure I’m in good health” or as serious as “I’ve lost twenty pounds is the past six weeks and I don’t know why”.

The history of the present illness is then taken. What are the main symptoms? When did they first appear? What makes them better and what makes them worse? Have they remained stable over time or are they increasing in intensity? These and similar questions define the current challenge as completely as possible.

The individual’s past medical history is then explored. What illnesses have occurred in the past? What operations have been performed? Does the person have any allergies? Is he or she on any medications? Are any nutritional supplements being taken? These factors may shed more light upon the current situation.

A family medical history is also important. What diseases tend to run in the family? At what ages have family members died? Has anyone in the family had a problem similar to the one the individual is currently experiencing?

The personal and social history is reviewed. What is the typical diet? How much physical activity is performed? What is one’s educational background and what occupations have been performed? What is the current living situation? What are the person’s religious beliefs and practices?

This is followed by a complete review of symptoms. Each body system is explored. Common symptoms are suggested to jog the person’s memory. The symptoms may more clearly define the primary illness or they may reveal additional challenges. The process of drawing out every symptom is important because symptoms are the body’s warning signals, like the oil and temperature lights on an automobile’s dashboard.

While the medical history supplies 85 or 90 percent of the available information, the physical examination provides an additional 7 to 10 percent. Height and weight measurements are taken along with vital signs such as the blood pressure and pulse rate. A careful head to toe examination using the skills of visual inspection, auscultation (listening), percussion (tapping for areas of brightness or dullness), and palpation (feeling and probing) follows. The amount of information that can be successfully gleaned from a skillful physical examination is reflected by the fact that Degowin & Degowin’s classical book on the subject encompasses nearly 1100 pages.

By the time a comprehensive history and a physical examination have been completed, medical tests – all medical tests, including blood tests, x-rays, electrical tracings, and scans – are likely to reveal only an additional 3 to 5 percent of the information available regarding an individual’s health status. Tests should be done to confirm what is already suspected; they should not be conducted for the sake of determining what challenge or challenges an individual is facing.

When I first began practicing medicine I frequently ordered tests to confirm the impression I had formed on the basis of my history and physical examination of a patient. On the few occasions when I turned to the laboratory for help in the diagnostic process I experienced a feeling of desperation and near panic. I knew that the tests were very unlikely to provide the clue I needed to determine what was wrong with the patient. As my confidence as a physician grew I came to rely upon laboratory tests less and less. Today I rarely order them.

Using blood tests as a starting point in determining one’s condition is standing the evaluation process on its head. It has become a common practice in today’s medical environment where time is at a premium. Nevertheless, looking at a battery of test results is often no more enlightening than reading tea leaves. When asked to do so I feel more like a gypsy fortune-teller than a caring physician.

Medical studies can be valuable when viewed in the context of a thorough evaluation. They can be worse than useless when they are examined independently. Beware of any physician visit that begins in the laboratory and avoid the temptation to rely upon periodic blood tests in determining your present and future state of health.