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How Reliable is Laboratory Testing?

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What types of things could compromise the integrity of a test and what is done to minimize them?

Laboratory testing is subject to many factors that potentially could adversely affect the integrity of the sample and prevent the timely reporting of an accurate test result to your provider. Typically these are grouped into three areas that track the sample from beginning to 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 obtained and includes how and when it is reported to your provider.

Pre-Analytic Activities
From the time a test is ordered, a chain of events is set into motion. All these steps must be done the right way to assure that an acceptable sample arrives at the lab. The following are some of the areas where errors can occur, and standard procedures are in place to prevent such errors.

  • Test ordering process – the provider or a staff member must order the correct test using the correct name or code.
  • Patient preparation for the test – the patient should have received appropriate instructions about diet, fasting, medications, etc. to assure that the sample will not contain substances that interfere with the test.
  • Patient identification – the person collecting the sample needs to confirm that the person is indeed the patient on whom the test was ordered. In hospitals, this means checking for a wrist band and confirming proper identification of the patient.
  • Completeness of patient information – the sample must be carefully labeled with two identifiers (usually patient name and date of birth or medical record number and the date of service) to assure that the sample is associated with the patient and not another person with the same name. A hard copy requisition or electronic version must accompany the specimen and includes the tests ordered, patient's demographics, ordering practitioner's demographics, date of service, and the phlebotomist's identification.
  • Specimen collection procedures – the sample must be collected in the correct type of container and mixed with the right preservative. The lab staff who collect samples receive special training on how to collect samples for each kind of test.
  • Transport to the lab – some samples need to be kept cold, while some need to be processed and tested within a limited time, so careful handling and prompt transportation are important components to sample integrity.

Automated ordering systems are increasingly used to expedite orders and minimize errors in sample collection and test requests. Use of computer technology (Laboratory Information System or LIS) allows health care providers to quickly input the test orders themselves. Since there are thousands of laboratory tests that may be selected from a laboratory's test menu, this process minimizes the chance for misunderstanding of 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.

A critical basic step in reporting accurate information is the correct identification of the person from whom the sample is collected. All laboratories are required to implement guidelines that include at least two different identifying methods (such as patient name and ID number) for both the person and their sample. When you are asked to give your name and some other identifying information, it is to assure that you and your sample are correctly matched. If this isn't done when a sample is taken, make sure you check to see that your sample is identified correctly.

For some tests, your diet, medications, and exercise history are important for proper interpretation of results. In some cases, special preparation must be taken to get reliable results for a test (such as fasting overnight before blood glucose and cholesterol are checked). A patient who does not follow preparation instructions or provides insufficient information to the health care provider undermines the entire quality assurance effort for a specific test.

Analytic Activities
Many test methods use automated analyzers, thus minimizing opportunities for human error. In the past decade or so, integrated computer technology has greatly enhanced the ability to accurately and consistently manage proper specimen identification, process of specimen testing, and test result reporting. In addition, these complex instruments can incorporate surveillance systems to detect malfunctions or other discrepancies and bring them to the attention of the laboratory staff.

Once the specimen is received in the laboratory, quality assurance procedures guide and monitor all related activities and include the following:

  • Instrument operations – all instruments are calibrated and tested regularly according to a standard protocol that addresses quality control, maintenance, and operation.
  • Valid test reagents – all test materials have an expiration date. The lab has routine procedures to make sure that test materials are good and have not gone past their expiration date.
  • Testing personnel – laboratory personnel who perform the testing must meet certain educational and training criteria. Many are professionally certified and in some states required to be licensed in order to perform laboratory testing.

Post-Analytic Activities
After the test is completed, the result must be delivered in a timely fashion to the health care provider.

  • Report sent to appropriate party – the report needs to be sent to the provider who ordered the test and any other health care professional identified to receive the report in order to diagnose, treat, or manage their patient.
  • Timely reporting of data – for most laboratory tests, an expected turn-around-time (TAT) is established and is often monitored as part of the quality assurance program.
  • Reference intervals – laboratory reports must include a framework for interpreting the results, which is referred to as the "reference interval." Each laboratory must establish a reference interval for every test they offer or provide a written interpretation of the test results. Variations in these intervals may be observed from laboratory to laboratory due to differences in instrumentation or testing methods. They also may be adjusted for biological factors such as sex, age, or other clinical situations. When a specific test is used to monitor a patient over a period of time, using the same laboratory to obtain those results provides a level of consistency to the treatment plan.
  • "Critical limits" – each laboratory has in place a system for immediate reporting to the ordering physician any finding that reflects a critical or life-threatening condition. When a test value falls within the critical limits, immediate action is required. Failure to report critical values may result in a patient's death or a medical condition that can not be reversed.

Most laboratory results are collated and managed by a sophisticated computer system (Laboratory Information System or LIS) capable of sending electronic reports to the health care provider by directly printing the report in a physician's office, 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 physician focus on the tests that are of most concern.

Here is one example of a laboratory report containing the elements described above.

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