TESTS: UNDERSTANDING LAB TESTING

Purpose of Lab Testing

Laboratory testing is one small part of your doctor's assessment of your health status. After taking a medical history and performing a physical examination, the doctor may decide that certain tests are indicated. Reasons to order laboratory tests include:

· As part of a routine overall health maintenance evaluation

· To confirm a clinical impression or to make a diagnosis

· To rule out a disease or diagnosis

· To provide information on the likely course and outcome of a disease (prognostic)

· To provide guidelines on how to treat a disease or condition (therapeutic)

· To screen for disease

Types Of Testing

Of the many thousands of available laboratory tests, among the most commonly ordered are the CBC (Complete Blood Count), the CMP (Comprehensive Metabolic Panel), and the urinalysis.

CBC
The CBC looks at the cellular elements within the blood. This test counts the:

· White Blood Cells (WBC) — Fight infection

· Red Blood Cells (RBC) — Carry oxygen. Hemoglobin and hematocrit levels indicate anemia.

· Platelets — Initiate the clotting of blood

CMP
The CMP measures the concentration of several different chemicals within the blood. Abnormalities in these tests could indicate:

· Sodium, Potassium, Chloride (Electrolytes) — Problems with hydration status or various disease states

· Bicarbonate — Problems with oxygen delivery and/or infection

· Glucose — Impaired glucose tolerance or diabetes mellitus

· Blood urea nitrogen, Creatinine — Kidney disease

· Calcium — Problems with bone and muscle health or certain endocrine disorders

· Protein, Albumin — Liver disease, or nutritional status

· Bilirubin, AST, ALP, ALT (Liver Function Tests) — Diseases of the liver such as alcoholism, infection or malignancy

Urinalysis
While the CBC and CMP require taking a sample of blood, a urinalysis requires a urine sample. Urinalysis includes a visual examination and chemical testing. The visual exam may help to detect bleeding or infection in the kidneys or bladder. The chemical analysis will reflect the kidneys' ability to concentrate urine and detect levels of protein, blood, glucose and ketones in the urine.

Get Your Results

Always make sure that your doctor shares the results of lab work with you. If your physician's office has not notified you of the findings within a week, call the office and request the results be discussed with you. Never assume that a test is normal just because you have not been informed otherwise.

Pathologists

A pathologist is a medical doctor who specializes in the diagnosis and classification of diseases by examining tissue, blood and body fluids. Doctors in all fields consult pathologists to help diagnose patients.

Reliability of Lab Tests

There are four concerns that help determine how good a lab test can be. A test is accurate if it measures what it is supposed to measure. A test is precise if it gives the same results over and over. Specificity and sensitivity measure the likelihood of a false-positive or false-negative reading.

One of the most important factors in determining the accuracy and reliability of your lab test is you, the patient. It is essential that you follow the instructions to prepare for the test you are having. Tell you doctor about any medications (including herbal remedies) you might currently be taking or foods you have eaten prior to the test. Excessive exercise, dehydration, excessive eating, or recent sexual activity can also affect test results.