Phases of diagnostic testing - the complexities involved

Dr Th Dhabali Singh MD *

Diagnostic testing in a laboratory is a complex process with many variables that act upon one another and that depend on strict adherence to protocols designed to minimise errors and maximise test reliability. These protocols are defined in the three distinct phases of testing: Pre-analytical, Analytical and Post-analytical. These phases are unique and have their own characteristics to influence testing in different ways. Let us examine them separately.

Pre-analytical phase of testing

The largest number of variables are found in this phase of testing. It is observed that of the three phases, the pre-analytical phase is most prone to errors. In this phase, many of the variables are related to the communication between the patient, the healthcare provider, and laboratory personnel. The following list will help us understand these variables more meaningfully:

Test requisition and communication
i) Tests are registered correctly, and there is proper communication between the patient and the one who’s registering.
ii) Correct information (patient name and demographic details, referring doctor are recorded electronically in the Laboratory Information Systems (LIS) by the receptionist.

Patient status and preparation
i) Stable health is desirable, as the physical or emotional stress or acute illnesses are among several factors that can affect some test results.
ii) Some tests require overnight fasting.
iii) Dietary or drug restrictions prior to testing might be required.

Sample collection

i) Collecting samples from the right patient and properly labelling the sample containers with patient identifiers, such as name, date of birth, patient ID number, etc.
ii) Right type and number of samples matched to the test to be performed (blood, urine, sputum, CSF fluid).
iii) Good quality and quantity of sample must be provided.
iv) Mixing of appropriate additive to the blood sample immediately after collection may be required in some cases.
v) Other factors like prolonged tourniquet use, difficult blood draws and small needles could cause the blood cells to break and affect the test results.

Sample transportation, processing and storage

i) Samples kept at room temperature for a long period of time or extreme exposure to light can affect the results of some tests.
ii) Excessive heat, freezing and rough handling can damage blood samples.
iii) Sample should be stored and stability maintained for further testing.

The analytical phase

o The quality of the test results relies on the analytical instrument to perform the test correctly and on the laboratory staff to identify and resolve any quality issues that arise. Typical areas of concern that the staff be aware of include:
o Analytical instrument status, equipment calibration and maintenance as well as the potential failure of an equipment because of a faulty component.
Interference due to sample condition or other issues. All technicians should have a good understanding of the limitation of the test methods used.

o Reagents, kits, controls and standards are acceptable and stable.
o Accurate identification of the samples by the analyser through barcodes.
o The LIS provides the correct information of the test to be performed and this is communicated to the analysers to ensure that everything is correct.
o Test is performed correctly through the many steps and completed within the turnaround time.

When any of the mentioned factors are not properly managed, the result may not reflect accuracy, precision and specificity required for correct results and an accurate interpretation.

The post-analytical phase The final stage of testing, this is where the results are printed and sent to the health care provider, who interpret the contents of the patient’s history and presentation of symptoms to devise a plan for further course of action. Post-analytical variables that can impact the results include:
o Right test results communicated from the analysers to the LIS and into its archives.
o Timely communication of the results to healthcare providers or patients for critical tests for a prompt intervention.
o Correct report with correct values and patient particulars, reference ranges to aid interpretations with abnormal results flagged properly.
o Proper interpretation of the test with additional information on the test/methodology limitations communicated properly.
o Results with appropriate recommendations are communicated thoroughly.

Laboratory management involves good team work

All diagnostic tests, regardless of what role they play in the patient care or what technology is used to perform them, require an acceptable level of accuracy and precision, sensitivity and specificity in order to demonstrate that they are effective. Diagnostic testing in a laboratory is a complex process and what the patient sees of the process and what the healthcare provider who prescribes the test sees is only a small fraction of the process. Laboratory management or the management to reduce or eliminate errors requires a good team effort.

Testing-related errors typically are not due to the quality of the test itself, but arise mostly during the pre- and post-analytical phase of testing. Diagnostic errors may happen when the test results are not properly communicated or used properly to inform the treating physicians or healthcare providers.