Reliability of test reports

Dr. Th. Dhabali Singh *

Clinical laboratory testing is, for many people, an unfamiliar side of medical care. Yet many of the decisions taken by a healthcare provider about one's health status - obtaining a diagnosis, developing a course of action for treatment, or monitoring the body's response to therapy - are based on laboratory data.

STANDARDS OF LABORATORY TESTING

All laboratory test methods must meet scientifically rigorous criteria before they can be used in clinical practice. This is to ensure that:

- ' The test is accurately able to detect or measure the substance it claims to detect or measure.

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 laboratory must indicate that it is able to perform a test in a clinically acceptable way. Certain agencies (NABL is one example) monitor the laboratories and set standards that a laboratory must meet in order to be allowed to perform the test. Some of these standards are:

Laboratories must perform routine quality control tests, usually every day, and in many cases, 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.

Laboratories must participate in proficiency testing programmes in addition to 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 the results to other participating laboratories, noting similarities or differences that may be attributed to the testing methodologies used. The laboratory must get the right result in order to be allowed to continue to test patient samples. If the lab repeatedly fails to get the right results, it is prohibited from continuing the performance of that test until it can demonstrate that it has corrected the problems that led to the unacceptable results.

Laboratories must demonstrate that they have written policies and procedures in place to specifically document how the sample is collected, transported, evaluated, and reported in an appropriate manner. These requirements ensure that the tests performed by clinical laboratories for patient care will generate results that are reproducible and can be trusted.

INDICATORS OF TEST RELIABILITY

Four indicators are most commonly used to determine the reliability of 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 is able to distinguish disease from absence of disease.

The accuracy and precision of each test method are established and are frequently monitored by the professional laboratory personnel. Sensitivity and specificity data are determined by research studies and are generally found in medical literature. Although each test has its own performance measures and appropriate uses, laboratory tests are designed to be as precise, accurate, specific and sensitive as possible.

These basic concepts are the cornerstones of reliability of one's test results and provide the confidence the healthcare provider has in using the clinical laboratory.

ACCURACY AND PRECISION

Statistical measurements of accuracy and precision reveal a lab's basic reliability. These terms, which describe sources of variability, are not interchangeable. A test method can be precise without being accurate or vice versa.

(i) Accuracy (trueness): A test method is said to be accurate when the test value approaches the absolute "true" value of the substance (analyte) being measured. Results from every test performed are compared to known "control specimens" that have undergone multiple evaluations and compared to the "gold" standard for that assay, thus analysed to the best testing standards available.

(ii) Precision (Repeatability): A test method is said to be precise when repeated analyses on the same sample give similar results. When a test method is precise, the amount of random variation is small. The test method can be trusted because results are reliably produced time after time.

SENSITIVITY AND SPECIFICITY

The tests that a provider chooses in order to diagnose or monitor a medical condition are based in their inherent ability to distinguish whether one has the condition or not. Depending on the symptoms and medical history, a doctor will ask for tests to confirm a condition or to rule out the condition.

(i) Sensitivity: It is the ability to correctly identify individuals who have a condition or a disease. The more sensitive a test, the fewer false-negative results will be produced.

(ii) Specificity: It is the ability of a test to correctly exclude individuals who do not have a given disease or condition.The more specific a test, the fewer false-positive results it produces.

TESTS THAT REQUIRE SUBJECTIVE EVALUATION

A laboratory also performs several tests and investigations that require more of subjective evaluation such as biopsy, cytology, etc. The experience and knowledge of the healthcare professional are of paramount importance in the evaluation of these parameters to deduce a conclusive diagnosis.

CONCLUSION

Laboratory testing is a science professionally conducted with rigorous statistical analysis, quality controls, and extensive oversight. Medical testing is an important component in the diagnostic tool kit of a healthcare provider. However, it is most reliable when used in conjunction 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.