CONTROL OF PRE-ANALYTICAL VARIABLES

CONTROL OF PRE-ANALYTICAL VARIABLES

Most of the error (>50%) which leads to variation and bias in the result are due to Preanalytical errors and identification Preanalytical components and controlling them to maintain the quality report includes,

System analysis:

The laboratory process starts from the time a physician request for a test to the time of final interpretation of the test result and this whole step constitutes the system. System analysis can identify error prone steps which should be paid most attention. Various error during the process are listed below

a.     Test ordering – the potential errors are inappropriate test, handwriting not legible, wrong patient identification, etc.

b.   Specimen collection – Incorrect tube or container, incorrect patient identification, inadequate volume, invalid specimen (e.g., hemolyzed or too dilute), collected at wrong time, improper transport conditions.

c.    Analytical measurement – Instrument not calibrated correctly, specimen mix up, incorrect volume of specimen, interfering substances present, and instrument precision problem.

d.      Test reporting – wrong patient identification, report not posted in chart, report not legible, report delayed, and transcriptional error.

e.    Test interpretation – interfering substances not recognized, specificity of test not understood, precision limitations not recognized, analytical sensitivity not appropriate, previous value not available for comparison, report not legible.

Types of Preanalytical variables

Monitoring the Preanalytical variables requires the coordinated effort of many individuals and hospital departments, each of which must recognize the importance of these components in quality of service. Variable to consider include the following:

Test usage and practice guidelines – 

The need of test and its cost effectiveness should be identified. There must be guidelines that indicate which tests are needed according to the availability and frequency of requests. There must be careful monitoring of test requests and their appropriateness so that laboratory can make adjustment according to the test requested.

Patient identification –

Identification of patients and specimen is a major concern for laboratories. Most of the errors occur due to improper identification of patient. One method for checking identification is to compare identifiers such as patient’s name, hospital number. The identification on the specimen label should also correspond with the identification on the requisition form. The integration of bar code technology into the analytical systems has significantly reduced identification problems.

Turnaround time – 

Delayed and lost test requisitions, specimens and reports have been major problems for laboratories. An essential feature for monitoring the cause of delay is the recording of the actual time of specimen collection, recipient in the laboratory and reporting test results. Listing of delayed specimens also provide a powerful mechanism for detecting lost specimens or reports. System analysis to identify the areas causing delays and disruption in service can help to address the problem. Laboratory should have record of patient tests so that if the report is lost then it can be retrieved anytime in need.

Laboratory logs– 

Once the serum tube arrives in the laboratory, various logging and monitoring systems are necessary. One should check that patient name and identification number and the test requested on the form match the information on the label of the specimen tube. The specimen should be inspected to confirm adequacy of volume and freedom from problems such as lipaemia or hemolysis. The specimens are then stored appropriately and identification information and arrival time are recorded in master log. After analysis, the results are recorded on the worksheet, and if both the assay and the individual test results pass the QC criteria, the test results are transferred to the result forms for reporting. Transcription error should also be checked and recorded.

Transcription errors – 

Transcriptional errors are more if manual system is there for entry of data. Computerization can reduce these errors.

Patient preparation – 

Proper patient preparation is essential to reduce error. Controllable variables that can affect the result should always be aimed to control. For each and every analyte laboratory should have proper procedures and guidelines for patient preparation. Before collecting samples these procedures should be given to patient either orally or in written form. E.g. fasting specimen, collecting timed urine, collection of blood for catecholamines, etc.

Specimen collection – 

There should be proper guidelines for specimen collection for various analytes. For example prolonged tourniquet application causes local anoxia to cells and this cause small solutes like potassium to leak from cells, protein concentrates in that area which give erroneous results. Blood collected from an arm into which an intravenous infusion is running can be diluted or contaminated. 

Hemolysis occurring during and after collection alters the concentration of analyte. Improper containers and incorrect preservatives greatly affect test results. One way to control this is to have a specially trained laboratory team assigned to specimen collection. Errors detected by limit checks, delta checks (difference between consecutive results on individual patients), or other algorithms should be recorded. Adequacy of specimen during collection should also be considered which will eliminate resampling.  

Specimen transport – 

There should be proper guidelines for specimens transport other wise there may be delay in getting the specimen and analytes alters. Also during transportation specimen may go to wrong location, especially if it is not well labeled. So there must be proper mechanism and person assigned for specimen transport in time. Patients should not be allowed to carry themselves the specimens. In controlling specimen transport, the essential feature is the authority to reject specimen that arrive in the laboratory in an obviously unsatisfactory condition (such as hemolyzed, thawed specimen that should have remained frozen, etc.).

Specimen separation and aliquoting – these includes

·     Centrifuge performance – the centrifuges should be in good condition and this is checked by monitoring speed, timer and temperature

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 Container monitoring – collection tubes, pipettes, stoppers, and aliquot tubes are sources of calcium and trace metal contamination.  Cork stoppers should not be used on specimens intended for calcium determinations because false elevations may occur. Plastic containers can adsorb trace amounts and should not be used for substances in low concentration, such as parathyroid hormone.

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 Personnel monitoring – The personnel who process the laboratory specimens should be carefully trained and supervised. A procedure manual should be available in processing desk. A performance of processing personnel should be checked. An important part of checking performance is throughput time (number of jobs per given time, or output per given input in given time), which can be calculated if one records the specimen arrival time and time when processing is completed. In optimizing the efficiency of a specimen processing laboratory, there is trade off between the time it takes to record and check parameters and the error rates or inconsistencies of the function.