Last updated on October 23rd, 2022 at 10:14 am
For many people, clinical laboratory testing is an unfamiliar side of medical care. Yet many of the decisions you and your doctor make about your health status, getting a diagnosis, developing a course of action for treatment, or monitoring your body’s response to therapy are based on laboratory testing data.
The Facts of the Laboratory Testing
Quick Jump Table
Your doctor trusts the results coming from the medical laboratory, and that trust is well-placed. 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.
- the test can accurately 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.
A pathology laboratory must show that it can perform that test clinically acceptably. State and federal regulatory agencies monitor the laboratory and set standards that a laboratory must meet to be allowed to perform the test. Some of these standards are:
- Medical Laboratories must perform routine quality control tests, usually every day, and most times, several times a day. Quality control tests usually include normal and abnormal samples to ensure that the equipment, the technologist, and the reagents used in the test are performing to established standards.
- Clinical Laboratories must take part in proficiency testing programs besides quality control testing. For proficiency testing, an external agency sends “challenge” samples to be tested. The laboratory must report results back to the agency. The agency has already evaluated each of the challenge samples and knows the expected results. This evaluation also compares results to other taking part laboratories, noting similarities or differences that may be attributed to the testing methodologies used. The laboratory must get the right result to be allowed to continue to test patient samples. If the lab repeatedly cannot get the right result, it is prohibited from continuing the performance of that test until it can show that it has corrected the problems that led to the unacceptable results.
- Pathology Laboratories must show that they have written policies and procedures in place to document how the sample is collected, transported, evaluated, and reported appropriately.
These requirements ensure the tests performed by clinical laboratories for patient care will generate results that are reproducible and can be trusted.
Some of the statistical indicators that are used to assure that both the test method and the laboratory performing the test are meeting acceptable standards are described in the next few pages, along with descriptions of other ways in which laboratories assure reliability.
What are the indicators of laboratory testing reliability?
Four indicators are most commonly used to determine the reliability of a clinical laboratory test. Two of these, accuracy and precision, reflect how well the test method performs day to day in a laboratory. The other two, sensitivity and specificity, deal with how well the test can distinguish the disease from the absence of disease.
- Accuracy and Precision
Statistical measurements of accuracy and precision reveal a lab test’s basic reliability. These terms, which describe sources of variability, are not interchangeable. A test method can be precise (reliable reproducibility) without being accurate (measuring what it is supposed to measure and its true value) or vice versa.
Although a test that is 100% accurate and 100% precise is an ideal test method, instrumentation, and laboratory operations all contribute to small but measurable variations in results. The small amount of variability that typically occurs rarely detracts from the test’s value and statistically is insignificant. The level of precision and accuracy that can be got is specific to each test method but is constantly monitored for reliability through comprehensive quality control and quality assurance procedures.
Therefore, when your blood is tested more than once by the same laboratory, your test results should not change much unless your condition has changed. There may be some differences between laboratories in precision and accuracy because of different analytical instrumentation or methodologies. However, the test results are reported with standardized reference intervals specific to that laboratory. This helps your healthcare provider to interpret the information and its relevance to that reference interval.
- Sensitivity and Specificity
The tests that a doctor diagnoses or monitors a medical condition are based on their inherent ability to distinguish whether you have the condition or do not have the condition. Depending on the symptoms and medical history, a doctor will order tests to confirm a condition (tests with high sensitivity) or tests to rule out the condition (tests with high specificity).
- Quality Control
Laboratory testing is subject to many factors that could adversely affect the integrity of the sample and prevent the timely reporting of an accurate test result to your doctor. Typically, these are grouped into three areas that track the sample from the end of the process.
- Pre-Analytical is the term used to describe things that happen from the time the test is ordered to the time the sample arrives in the lab.
- Analytical is the term used to describe the things that happen during the handling and analysis of the sample in the laboratory.
- Post-Analytical is the term used to describe what happens after a result is received and includes how and when it is reported to your doctor.
Laboratory Information System or LIS
Most laboratory results are collated and managed by a sophisticated computer system (Laboratory Information System or LIS) capable of sending electronic reports to the doctor by directly printing the report in a doctor’s office with a dedicated printer, by email, or by automated faxing. These computers can track test orders, provide pre-analytical information, assist in quality control and quality assurance procedures, alert laboratory staff of an unusual finding such as a critical value, and report and store all laboratory results. Laboratory reports generated by the system can also highlight values that fall outside the expected or reference interval to help the provider focus on the tests that are of most concern.
Automated ordering systems are increasingly used to expedite orders and minimize errors in sample collection and test requests. Using computer technology (Laboratory Information System or LIS) allows the doctor to input the test orders themselves.
Since thousands of laboratory tests may be selected from a laboratory’s test menu, this process minimizes the chance of misunderstanding what tests are desired. Many of these systems can generate labels that include a bar code for tracking and identification of a patient and the specific tests ordered. It can also provide supplemental information on the sample size needed (how much blood needs to be drawn), types of containers or blood tubes to be used to collect the sample, and information about handling, transporting, and storing samples.
For some tests, your diet, medications, and exercise history are important for proper interpretation of results. Sometimes, special preparation must be taken to get reliable results for a test (such as fasting overnight before blood glucose or cholesterol is checked). A patient who does not follow preparation instructions or provides insufficient information to the doctor undermines the entire quality assurance effort for a specific test.
The Role of Laboratory Testing in the Patient Diagnostic Process
A doctor is expected to evaluate all the relevant findings, laboratory test data plus information from other sources, such as a physical exam, personal and family histories, signs and symptoms, and other diagnostic examinations, i.e., X-rays, ECG, etc. before settling on a diagnosis and developing a treatment plan. Given the complexities in human physiology and disease response, no diagnosis should ever be made solely based on a single lab test.
The clinician must always ask, “Do the test data fit with the other pieces of the puzzle?” Careful evaluation and consideration of test findings increase the reliability of a diagnosis and can reduce the chance of medical errors.
Data from medical tests are part of the information set that needs to be considered when a doctor makes a diagnosis. When a laboratory report shows abnormal results, it is incumbent on your doctor to further evaluate and corroborate the information at hand to ensure an accurate diagnosis. If the data does not correspond with the clinical picture, additional information may be needed and retesting may be appropriate. In some situations, the progression of the disease or condition may not be clear for the testing modality to be relevant.
Conclusion on Laboratory Testing Services
- Laboratory testinguri is a science professionally conducted with rigorous statistical analysis, quality controls, and extensive oversight. Medical lab testing is an important component in the diagnostic tool kit of a doctor. However, it is most reliable when used with other meaningful data collected in the diagnostic process, when appropriate questions are asked and answered, and when there is open communication between healthcare teams and patients.
- You can put great trust in the data generated by today’s exacting medical tests. A caveat to remember is that a diagnosis and treatment plan for a serious disease should never be based on a single medical test. Test findings are just one piece of the diagnostic puzzle.
- Help your doctor with interpreting the data by providing thorough information on your medical history and keeping track of symptoms you wish to report. To reduce the chance that you are improperly diagnosed and given potentially harmful and unnecessary medical procedures, first follow test preparation instructions carefully and tell your doctor and the person collecting your sample (lab technician) about any exceptions you have made.
- Accessing your lab report after you have testing done is a good way to stay informed and you can follow up with your doctor if you have questions concerning your test results.
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