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Diagnostic lab test

Did you ever wonder what your medical lab test results mean? Lab test results interpretation should be done by a medical professional. But it will help you to understand your lab test results well if you know some basic about medical lab test, including the procedures, reference values and interpretation.

Symptoms generally lead to lab tests and radiographs, depending on the situation. Blood tests are a key step in the evaluation. Depending on what symptoms you might have, your doctor may want to obtain a urine sample, throat swab, or other sample. Follow the instructions carefully; the right sample leads to the right lab test results.

Lab tests are generally done for one of the following reasons: To find the cause of symptoms, to confirm a diagnosis, to assess the severity of a disease, to monitor the progression of a disease, how well an organ is working, or if treatment is helping, to verify specific events and to screen for a disease, Screening tests are often done for people of a specific age or those who have a high risk for a specific disease.

Lab test results are very important to your health care, but in most cases lab test results don’t provide all the information your doctor needs to make a diagnosis or treatment decisions. Unless the test results are very clear, for example, you are pregnant or you’re not, your doctor will rarely make a decision or diagnosis based only on one lab test result. Many conditions can change your lab test results. Your doctor will talk with you about any abnormal results as they relate to you. Your healthcare provider will use your lab test results along with information about your health, gender, age, and other factors.

Although lab test results may not provide all of the information that your doctor needs, the lab test results help him or her make a diagnosis. Understanding your lab test results will help you and your doctor discuss the next step in your diagnosis or treatment.

Lab test procedures

After the sample is collected, the container is labeled with your name and other information.

When the sample gets to the laboratory, it is logged into the hospital computer. It’s then given to the laboratory staff who will perform the testing.


In the Chemistry section of the lab, blood and other body fluids are tested for chemicals, drugs and substances that indicate disease. Examples of Chemistry tests include cholesterol and other tests for risk of heart disease, glucose to monitor diabetes, cyclosporin to help physicians give the correct dose of this powerful drug, and thyroxin to monitor the thyroid gland.


Examples of Hematology tests include the Complete Blood Count (CBC) that tells the doctor how many cells of each type are in your blood.

Immunology/Molecular Diagnostics

The Immunology/Molecular Diagnostics laboratory performs a wide variety of complex tests. Some tests are used by your doctor to determine whether your immune system is functioning properly.


The Microbiology section of the lab tests patients for infections caused by bacteria, fungi or parasites. Many types of specimens — including blood, urine, sputum, stool and others are tested. An example of a Microbiology test is a urine culture for urinary tract infections.


The Virology laboratory tests for viral infections. Depending on the virus suspected, the laboratory might look for the virus directly, or test your blood to see if your immune system has reacted to a virus. Examples of Virology tests include rapid tests for respiratory viruses such as influenza, molecular tests for noroviruses, and antibody tests for HIV.

After the tests are done, lab test results are reviewed and entered into the hospital computer system. For lab test results that indicate the patient may be very ill, the laboratory calls the doctor with the critical lab test results.

Depending on how long it takes to carry out a particular test, the length of time between the drawing of the blood and when your provider gets the results can vary greatly, from as little as a few minutes to as much as several weeks. Most laboratory testing is done here, but some specialized testing is sent to other labs which are expert in particular tests.

Lab test results report

All lab test result reports must contain each of the elements required by CLIA (Clinical Laboratory Improvement Amendments). It may also contain additional items not specifically required but which the lab chooses to include to aid in the timely reporting, delivery, and interpretation of your lab test results.

Some items included on a lab test results report:

Patient name and identification number or a unique patient identifier and identification number.

Name and address of the laboratory location where the test was performed.

Test date and report print date.

Name of doctor or legally authorized person ordering the test(s). This information enables the lab to forward your results to the person who requested the test(s). Sometimes a report will also include your primary physician.

Specimen source,

Date and time of specimen collection. Some test results may be affected by the day and time of sample collection. This information may help your doctor interpret the results.

Laboratory accession number.

Name of the test performed.

Lab test results, some results are written as numbers when a substance is measured in a sample as with a cholesterol level (quantitative). Other reports may simply give a positive or negative result as in pregnancy tests (qualitative). Still others may include text, such as the name of bacteria for the result of a sample taken from an infected site.

Abnormal lab test results, Lab reports will often draw attention to results that are abnormal or outside the reference range by setting them apart or highlighting them in some way. For example, “H” next to a result may mean that it is higher than the reference range. “L” may mean “low” and “WNL” usually means “within normal limits.”

Critical lab test results, those results that are dangerously abnormal must be reported immediately to the responsible person, such as the ordering physician. Some labs will inform the patient or physicians immediately or as soon as possible.

Units of measurement (for quantitative results).

Reference intervals (or reference ranges). These are the ranges in which “normal” values are expected to fall.

The ranges that appear on your report are established and supplied by the laboratory that performed your test. They are made available to the doctor who requested the test(s) and to other health care providers to aid in the interpretation of the results.

Condition of specimen, any pertinent information regarding the condition of specimens that do not meet the laboratory’s criteria for acceptability will be noted.

Deviations from test preparation procedures.

Medications, health supplements, etc. taken by the patient. Some tests results are affected by medications, vitamins and other health supplements, so laboratories may obtain this information from the test request form and transcribe it onto the lab report.

Lab test results

Once the lab test results are reported, your provider will interpret them based his or her knowledge of you. The lab test results may help to rule out or diagnose disease, or to do the best possible job of managing a known disease. You should ask your provider to explain your lab results to you, so you can participate in maintaining your health.

Lab test results may be positive, negative, or inconclusive. Your doctor will discuss what your test results mean for you and your health.

A positive test result means that the substance or condition being tested for was found. Positive test results also can mean that the amount of a substance being tested for is higher or lower than normal.

A negative test result means that the substance or condition being tested for was not found. Negative results can also mean that the substance being tested for was present in a normal amount.

Inconclusive test results are those that are not clearly positive or negative. For example, some tests measure the level of antibodies to some bacteria or viruses in blood or other bodily fluid to look for an infection. It is not always clear if the level of antibodies is high enough to indicate an infection.

A false-positive test result is one that indicates a disease or condition is present when it is not present. A false-positive test result may suggest that a person has the disease or condition when he or she does not have it. For example, a false-positive pregnancy test result would appear to detect the substance that confirms pregnancy, when in reality the woman is not pregnant.

A false-negative test result is one that does not detect what is being tested for even though it is present. A false-negative test result may suggest that a person does not have a disease or condition being tested for when he or she does have it. For example, a false-negative pregnancy test result would be one that does not detect the substance that confirms pregnancy, when the woman really is pregnant.

Some lab test results can give you specific information. For example, your doctor may suspect you have strep throat and order a throat culture to see if streptococcus bacteria are present. A positive lab test confirms that you have strep throat and helps your doctor choose the right treatment for you.

But some lab test results give only a clue that must be considered with other information to support a diagnosis, identify a risk, or help choose a treatment. For example, if your cholesterol test results show you have high LDL (“bad”) cholesterol, your doctor will weigh your other risk factors for heart disease before deciding on treatment.

Many lab test results are expressed as a number that falls within a reference range. A reference range is determined by testing large groups of healthy people to find what is normal for that group. Each reference range is different because it is created from information from a specific group. For example, the following values show reference ranges for a sedimentation rate test. Men: 0-15, Women: 0-20, Children: 0-10 and new baby: 0-2 millimeter per hour.

Lab test result reference ranges

The term “normal range” is not used very much today because it is considered to be misleading. If a patient’s lab test results are outside the range for that test, it does not automatically mean that the result is abnormal. Therefore, today “reference range” or “reference values” are considered the more appropriate terms,

The tests use a range because what is normal differs from person to person. Many factors affect test results. These include your sex, age and race, what you eat and drink, medicines you take, how well you followed pre-test instructions. Your doctor may also compare your results to results from previous tests. Laboratory tests are often part of a routine checkup to look for changes in your health. They also help doctors diagnose medical conditions, plan or evaluate treatments, and monitor diseases.

It is possible to have a result that is different than the reference range even though nothing is wrong with you. The normal values for blood tests can be different from lab to lab. Blood tests can have false positives and false negatives. Interpretation of blood tests takes knowledge of the underlying disease process and experience.

Sometimes certain factors can affect your test results, such as pregnancy, a medicine you are taking, eating right before a test, smoking, or being under stress. When your lab numbers are lower or higher than the numbers in the reference range, further testing may be needed. Your doctor may want to repeat the test or order another test to confirm the lab test results.

Labs may use different types of equipment and tests, and sometimes they set their own reference ranges. Your lab report will contain the reference ranges your lab uses. Do not compare results from different labs.

Only a handful of tests, such as cholesterol and blood sugar, have standardized reference ranges that all labs use. This means that no matter where these tests are done, the results are compared to the same reference ranges.

Measurement units

Lab test results usually contain a number followed by a unit of measurement, such as 37 milligrams per deciliter (mg/dL). The units provide a way to report results so that they can be compared. Usually, but not always, the same test is reported in the same units no matter which lab did the test.

The units of measurement can vary from lab to lab. It is similar to the way, for example, your doctor chooses to record your weight during an examination. He may decide to note your weight in pounds or in kilograms. In this same way, labs may choose to use different units of measurement for your lab test results. Regardless of the units that the lab uses, your lab test results will be interpreted in relation to the reference ranges supplied by the laboratory.

Laboratory Information Systems

Laboratory Information Systems will enable authorized health care providers to view lab test results, regardless of where the test was conducted, when a patient is tested, whether at a clinic, hospital or other facility, Laboratory Information Systems will enable laboratory technicians to enter the results into a database accessible to authorized health care providers. Lab test results will be linked to individuals’ electronic health records, providing additional resources for diagnosing and treating patients. Authorized health care providers will be able to quickly access lab test results and reports leading to faster diagnoses and treatment, regardless of where the patient was tested. More efficient methods of securely storing and disseminating lab test results will lower costs by reducing the need for duplicate and unnecessary tests.

Clinical laboratory testing is held to very high state and federal regulatory standards. All laboratory test methods must meet scientifically rigorous criteria before they can be used in clinical practice. For commercial tests in the U.S., the Food and Drug Administration (FDA) reviews the scientific evidence to ensure that: the test is able to detect or measure the substance it claims to detect or measure, and the measurement or detection of this substance provides important information about an illness or about health status that assists in the diagnosis, treatment, or monitoring of a patient.


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