What types of things could compromise the quality of a test and what is done to minimise them?
Many things can change laboratory tests which could adversely affect the reliability of the result and prevent the timely reporting of an accurate test result to your doctor. These influences can be placed into three groups which relate to a process from sample request to it being reported.
- Pre-Analytical is the term used to describe things that happen from the time the test is requested 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 doctor.
When a test is requested, a chain of events is set into motion. All these steps must be performed correctly to ensure 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 requesting process – the doctor or nurse must request 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 requested. In hospitals, patient identification is usually checked on a wrist band and conversation with the patient.
- Completeness of patient information - the sample must be carefully labelled with three identifiers (usually patient name and date of birth and medical record number) to ensure that the sample is from the correct patient and not one with the same or similar name.
- Specimen collection procedures - the sample must be collected in the correct type of container and mixed with the right preservative. The laboratory 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 and some need to be transported quickly in the laboratory, so careful handling and prompt transport are important for sample integrity.
Automated test requesting systems (“order communications”) are increasingly used to minimize errors in sample collection and test requests. Computer technology allows health care providers to quickly request tests themselves and minimise the chance of misunderstanding and error. These systems can generate labels that include a bar code for tracking and identification and can provide supplementary information on the size of sample needed, the types of containers or blood tubes to be used to collect the sample, and procedures for handling and transport.
One of the key steps to getting correct results is proper identification of the person from whom the sample is collected and the sample itself. Safety guidelines require the use of at least three different identifying methods (such as name, date of birth and patient ID number) for identifying both the person and their sample. When you are asked to give your name and some other identifying information, it is to check 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. If you collect a sample (for example, an early morning urine collection) at home, make sure you use an appropriate clean container, and that the sample is labelled with your full name, date of birth and the time and date of collection.
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 lipids are checked). A patient who does not follow preparation instructions or provides insufficient information to the doctor or laboratory undermines the entire quality assurance effort for a specific test.
Once the specimen is received in the laboratory, quality assurance procedures guide and monitor all processes, including the following:
- Instrument operations – all instruments are calibrated and tested regularly according to a standard protocol that covers 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 in good condition and have not passed their expiration date.
Many test methods use automated analysers which minimise the opportunity for human error. Bar code readers read the sample tube label and associate the result with the correct patient. A robotic system carefully removes the exact amount of blood or urine needed for the test. The onboard computer monitors the test as it is in progress to assure that there are no unexpected occurrences during the analysis. Most instruments have internal computer surveillance systems to detect malfunctions or other discrepancies and bring them to the attention of the laboratory staff.
After the test is completed and the result generated in the lab, there are systems to deliver it in a timely fashion to the doctor or other health care provider.
- Report sent to correct place – the report needs to be sent to the provider who requested the test and any other health care professional who needs to receive a copy of the report.
- Timely reporting of data – there is an expected turn-around-time (TAT) for test results, with more critical results and results for monitoring of acute events needed more promptly than routine tests. Labs have a hierarchy of tests that are critical and special codes that can be used to assist in meeting medically necessary TAT.
- Reference intervals included - lab reports do not simply report a test result without providing a framework for interpreting the result – the “reference range.” Some lab computer systems can also suggest diagnoses, follow-up testing, and other insights that may help the provider interpret the result in the context of a particular patient.
- Immediate notification of results exceeding “critical limits” - each laboratory has in place a system for immediate reporting to the requesting doctor any finding that reflects a critical or life-threatening condition.
Most laboratory results are collated and managed by a sophisticated computer system capable of sending electronic reports to the health care provider by direct transfer to the GP’s computer or hospital information system. These computers can alert laboratory staff of an unusual finding, such as a critical value, and can alert the staff to call the physician. Laboratory reports generated by information systems can also highlight values outside the expected or reference range to help the physician focus on the tests that are of most concern.