Abstract
ContextRoutine repeat testing of critical values is a long-standing practice in many clinical laboratories; however, its usefulness and necessity remain to be empirically established and no regulatory requirements yet exist for verification of the critical value results obtained by repeat analysis.ObjectiveTo determine whether repeat testing of critical values is useful and necessary in a clinical chemistry laboratory.MethodsA total of 601 chemistry critical values (potassium, n = 255; sodium, n = 132; calcium, n = 108; glucose, n = 106) obtained from 72,259 routine clinical chemistry specimens were repeat tested. The absolute value and the percentage of difference between the two testing runs were calculated for each of the four critical values and then compared with the allowable error limit put forth in the College of American Pathologists (CAP).ResultsAmong the repeat data for the 601 critical values, a total of 24 showed large differences between the initial result and the repeated result which exceeded the CAP limits for allowable error. The number and rates (%) of large differences for within and outside the analytical measurement range (AMR) were 12 (2.1%) and 12 (41.4%), respectively. For the 572 critical values within the AMR for each test category, the mean absolute difference (mmol/L) and difference(%) between the two testing runs were: potassium, 0.1 mmol/L (2.7%); sodium, 2.1 mmol/L (1.7%); calcium, 0.05 mmol/L (3.0%); glucose, 0.18 mmol/L (2.6%).ConclusionsWhen the initial chemistry critical values are within the AMR, repeated testing does not improve accuracy and is therefore unnecessary. When the initial chemistry critical values are outside the AMR, however, the benefit of repeated testing justifies its performance and makes it necessary. Performing repeat clinical testing on a case-by-case, rather than routine, basis can improve patient care by delivering critical values more rapidly while providing savings on reagent costs associated with unnecessary repeat testing.
Highlights
When the initial chemistry critical values are within the analytical measurement range (AMR), repeated testing does not improve accuracy and is unnecessary
When the initial chemistry critical values are outside the AMR, the benefit of repeated testing justifies its performance and makes it necessary
Since Lundberg [1] first described a critical value as a laboratory result that reflects a potentially life-threatening emergency in 1972, well-defined requirements for the identification, handling, documentation and auditing of laboratory critical values have been published by the Joint Commission International, ISO 15189, and the College of American Pathologists (CAP) [2,3,4]
Summary
Since Lundberg [1] first described a critical value as a laboratory result that reflects a potentially life-threatening emergency in 1972, well-defined requirements for the identification, handling, documentation and auditing of laboratory critical values have been published by the Joint Commission International, ISO 15189, and the College of American Pathologists (CAP) [2,3,4]. The Chinese Hospital Association (CHA) has recently established the requirement of reporting critical values [5]. In many laboratories, repeat testing is performed as a routine practice prior to communicating the critical laboratory values to the caregiver. The reasoning for this repeat testing routine is to ensure the accuracy of results and to avoid reporting false or erroneous data. A Q-Probes survey of clinical laboratories conducted by CAP found that 61% performed routine repeat testing for critical chemistry values and identified the associated delay to reporting as 10 – 14 minutes; more importantly, neither the delay to reporting nor the related wasted resources were found to provide any significant benefit in preventing analytic errors [9,10]
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