Andress, B D

Abstract Background Serum aspartate aminotransferase (AST) is a commonly ordered test useful for diagnosing and monitoring hepatocellular damage. The hemolysis (H) index interference threshold for the Roche Cobas AST reagent is H=20, which is the lowest of all tests on Roche chemistry platforms (Cobas c701, c502, and e801). Previous optimization studies supported the implementation of an AST concentration-specific tiered hemolysis interference threshold schema: AST<100 U/L (H=50), AST=100-200 U/L (H=100), AST=201-300 U/L (H=200) and AST>301 U/L (H=500). This schema significantly reduced redraws; however, a significant number of rejected samples were noted to have AST results within the reference interval (RI). The aim of this study was to establish an H-index threshold for samples with AST results within the RI. Methods Twelve pools of residual serum samples were created with AST concentrations ranging from 17-66 U/L. Each pool was split into 2 aliquots, receiving either 10% of a lab-produced hemolysate solution generating H-indices from 62-508 or 10% of a 0.9% saline control. Aliquots were mixed in equal portions to create a series of 5 samples with increasing hemolysis according to CLSI guideline EP-07 and analyzed in EP Evaluator. Median(interquartile range (IQR)) H-index thresholds were calculated for error limits beginning at +5 U/L and increasing incrementally (+1 U/L) to +10 U/L. Clinical cases with an H-index slightly above the hemolysis interference threshold (50≤H≤70) and results within the RIs (Male:8-48U/L; Female:8-43U/L) were reviewed by the Chemistry Resident/Fellow on-call (n=68) over a period of 8 months. Results were released with a comment if risk of clinical misinterpretation due to a falsely elevated result was low. Previous, non-hemolyzed AST results were compared within 45 days, if available, by paired-Wilcoxon test (Graphpad Prism). Results The median(range) of initial AST results in the serum pools was 20(17-66) U/L. The calculated H-index thresholds (median(IQR)) using error limits of +5, +6, +7, +8, +9, +10 U/L were 49(43-53), 56(52-63), 66(61-78), 78(72-81), 91(84-91) and 101 (96-107), respectively. All slightly hemolyzed AST results (50≤H≤70) within the RI were released with a comment upon chart review. Previously reported AST values (n=23) were compared to current (hemolyzed) concentrations and found to be statistically significantly increased relative to previous results from the same patient (median(range) difference: 3.7(-3.6-11)U/L, p=0.009). However, the median difference was <5U/L or 10%, the laboratory’s criteria used to define a clinically significant difference. Conclusions A median H-index limit of up to 100 can be applied to samples when AST is within the RI. The risk of misinterpretation for results with mild-moderate hemolysis was low in the cases reviewed. Sample rejection rates and reporting delays can be diminished by implementing this practice. Interpretation can be further enhanced by appending the following comment to hemolyzed samples: “Specimen was received with hemolysis slightly above the accepted threshold. This degree of hemolysis is associated with a false increase of approximately 5-10 U/L. Interpret in conjunction with other laboratory and clinical findings.”

Abstract Background Serum cortisol, measured by automated immunoassay, is a rapid test used for the initial assessment of adrenal dysfunction. Physiologic serum cortisol concentrations are influenced by many factors including diurnal variation, stress, and patient age. In the absence of established pediatric reference intervals (RIs), our laboratory has utilized adult RIs to flag pediatric cortisol results as abnormally high or low in the electronic health record. However, pediatric cortisol RIs recently defined by the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER) are considerably lower than the adult RIs currently in use. This could cause pediatric cortisol results to be incorrectly flagged as “low” when they are within the age-specific RI and lead to unnecessary follow-up testing. The aim of this study was to determine the impact of implementing CALIPER pediatric cortisol RIs on the rate of “low” result flagging for pediatric patients. Methods AM cortisol results for patients age <18 years reported between 10/2012- 09/2022 were obtained from the Mayo Clinic data repository. These results contained values measured by both Beckman Access (n = 3 818) and Roche Cobas (n = 625) immunoassays. Results classified as abnormal “low” by current adult RIs (Beckman: 7–25 mcg/dL, Roche: 4.8–20 mcg/dL) were compared to results which would flag low according to the appropriate method- and age-specific RIs defined by CALIPER (Beckman: 1-<13 yrs 2.19–12.8 mcg/dL, 13-<16 yrs 3.03–17.1 mcg/dL, 16-<19 yrs 3.78–19.4 mcg/dL; Roche: <1 yr 0.58–17.2 mcg/dL, 1-<12 yrs 2.39–14.9 mcg/dL, 12-<19 yrs 3.63–17.4 mcg/dL). The proportion of results flagging low by adult versus pediatric RI were compared by chi-squared test, with P < 0.05 considered significant. Results For Beckman, the percentages of pediatric patient cortisol results flagging low using the adult RI versus (vs) the pediatric age-specific RI were: 35% vs 7% for 1–12 years of age (P < 0.001, n = 1866), 22% vs 5% for 13–15 years (P < 0.001, n = 966), and 16% vs 5% for 16–18 years (P < 0.001, n = 986). For Roche, the same analysis yielded: 52% vs 9% for 0–1 years (P = 0.001, n = 23), 14% vs 8% for 1–11 years (P = 0.03, n = 238), and 9% vs 6% for 12–18 years (P = 0.16, n = 364). Conclusion The implementation of pediatric RIs for serum cortisol will have a significant impact on the number of “low” result flags for patient results on both Beckman and Roche platforms. Statistically significant decreases in the percentage of low result flags were observed on both platforms for all age ranges except for the age bracket of 12–18 years by Roche. Furthermore, pediatric RIs appeared to produce more consistent rates of abnormal results across methods and age ranges, with all groups flagging low at a rate of 5–9%, whereas the same age ranges with adult RIs flagged at rates ranging from 9–52%. Lowering the RIs for pediatric cortisol to more appropriate ranges as identified by CALIPER will decrease the number of “low” flag results. This has the potential to decrease unnecessary follow-up, including repeat testing and further diagnostic procedures such as ACTH stimulation testing. Implementation of pediatric RIs has potential benefits regarding stress and cost for patients and parents, alarm fatigue for physicians, and utilization of laboratory resources.