Can't doctors tell what's wrong with my child by just examining him?

Most of the time, taking a history and performing a physical examination provide the information a doctor needs to evaluate how a child is doing or to understand the cause of an illness. Physicians spend years learning which questions are important to ask - and the meaning of the answers. In the case of an ill child, doctors are likely to ask when the illness first began, what the first symptoms were, how they changed over time, and often dozens of other specific questions that will shed light on the cause of the problem.

A Physical Examination Reveals Countless Clues
For example, the first thing a doctor does to evaluate respirations (breathing) is just watch the patient for a few moments. Such trained observation can give the doctor important information about the pattern and rate of breathing, the amount of effort required, the color of the skin and nailbeds, and more. Some observations are subtle and might even seem to have nothing to do with the respiratory system. For example, a type of change of the fingernail shape may be connected with chronically low blood oxygen. These physical findings can be signs of a number of different problems that have to be distinguished from each other. Sometimes what the doctor observes can be just a variation of normal.

After taking a history and performing an examination, the doctor must come up with a list of possible conditions that might be the cause of the problem. This is a list of the "differential diagnoses." Sometimes this list is short and simple, other times long and complex.

Sometimes More Information Is Needed
As revealing as the history and examination can be, sometimes more information is needed to fully understand what's going on. Although most are rarely needed, there are literally hundreds of laboratory tests and other studies that can be ordered (X-rays, CT scans, ultrasounds, etc.). Doctors have to decide which tests, if any, will significantly increase their understanding and affect the treatment. These studies may have "costs" - in dollars, pain, worry, and time. Sometimes a test isn't "sensitive" enough to spot a problem or is too sensitive and appears to identify a problem where there is none. Is it still worth ordering? All these factors (and more) are weighed in deciding whether or not to order a test . . . and which test to order.

Many times the right test will help a doctor make a diagnosis or eliminate a possibility. Most of the time, tests serve to support possible diagnoses. The test becomes one part (though an important part) of the information to be considered.

Some Common Lab Tests

• Complete blood count (CBC) helps to detect anemia or evidence of infection and gives information about whether a transfusion might be needed for a very sick child.
• Blood chemistry tests look for evidence of liver or kidney dysfunction, diabetes, metabolic disorders, and tissue damage.
• Serology and immunology tests look for infections or signs of autoimmune disorders.
• Endocrine tests look for causes of short stature or thyroid, adrenal gland, pituitary gland, or other hormonal problems.
• Microbiology tests on blood, urine, tissues, or other body fluids look for bacterial, fungal, tuberculosis, viral, and other types of infections.
• Newborn screening tests, often done by tandem mass spectrometry on blood spots placed on paper, look for problems with a newborn's metabolism and hereditary diseases (like phenylketonuria) which can interfere with growth and development if not detected and treated early.

Updated and reviewed by: Cheryl M. Coffin, MD
Date reviewed: May 2004
Originally reviewed by: Frederick Meier, MD, and Neil Izenberg, MD