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Performance studies on a nephelometric assay for alpha1-antitrypsin
Abstracts
Results: Raw p-values for significant tests were adjusted using the Bonferroni method to account for any significance seen due to multiple comparisons. Fasting had significant effects on 9/38 analytes, with HDL cholesterol being the most highly affected (p = 7 × 10 − 7). Values tended to decrease post-prandially, except for uric acid which increased. By ANOVA, 24 chemistries, including triglycerides, significantly differed across times of day tested. Analysis of individual time points showed differences between morning fasting and mid-afternoon samples. Conclusions: Fasting is necessary for analysis of certain chemistries in pediatric subjects. For most tests, food intake did not influence measured values, but there was variation depending on the time of day the test was done. Pediatricians should consider diurnal factors when ordering non-fasting tests. doi:10.1016/j.clinbiochem.2011.06.026
P516 Case report: Laboratory investigation of factitious hyperkalemia in a chronic lymphocytic leukemia patient Y. Gong a,b, G. Hoag a a Dept. Laboratory Medicine, Vancouver Island Health Authority, Victoria, BC, Canada b Biochemistry Division, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada Background: Preanalytical conditions, such as hemolysis, thrombocytosis, and leukocytosis, have been known to cause factitious hyperkalemia to various degrees. Objective: To report a case of severe factitious hyperkalemia due to chronic lymphocytic leukemia (CLL) and laboratory procedures to mitigate interference due to leukocytosis. Case summary: A 63-year-old male was admitted with bilateral bronchopneumonias and end-stage CLL. His original plasma potassium in lithium heparin tube measured on Beckman Coulter UniCel DxC (DxC), was 9.4 mmol/L. Same specimen, measured on Abbott i-STAT, gave potassium >9.0 mmol/L. However, a whole blood run on GEM Premier 4000 (GEM) at bedside showed potassium at 3.8 mmol/L. Patient's WBC was at 1012 × 10 9/L. On the second day, two separate samples (collected 1.5 h apart) were measured at 10.3 and 2.3 mmol/L on DxC. To further reveal the potassium status, a sample was carefully collected in lithium heparin tube, then tube was gently inverted twice to mix anticoagulant and carried back to the lab at 37 °C for immediate analysis. Whole blood sample was run on GEM and gave a potassium value of 4.0 mmol/L. After being centrifuged at 2000 rpm for 2 minutes, plasma specimen was measured at 4.7 mmol/L on DxC. Discussion: In the case reported, factitious severe hyperkalemia was caused by extreme leukocytosis due to CLL, probably because of white blood cell fragility coupled with mechanical stress during routine sample process procedure. Conclusions: Gentle and prompt sample process ensure that laboratory potassium measurement is valid in patients with extreme leukocytosis. A whole blood sample type can also facilitate confirmation of a valid patient result. doi:10.1016/j.clinbiochem.2011.06.027
P517 Performance studies on a nephelometric assay for alpha1-antitrypsin A.M. Grunbaum a, A. Mattman b, B.M. Gilfix a a McGill University Health Centre (MUHC), Montreal QC, Canada b St. Paul's Hospital (SPH), Vancouver, BC, Canada
1171
Objectives: Alpha-1 antitrypsin (AAT) deficiency is an underrecognised inherited disorder affecting primarily the lungs and liver. In the US, only 5% of an estimated 100,000 individuals with severe deficiency have been diagnosed, most commonly due to the Z allele variant. In an effort to establish cross-Canada referral centres for the diagnosis of AAT deficiencies, we report our validation of an AAT nephelometric assay and an inter-site correlation study. Methods: Serum specimens were collected from MUHC patients according to established protocols, and frozen at −20 °C until analysis. Validation studies were performed on a Beckman Immage 800 rate nephelometer and correlated against a Behring nephelometer (SPH). Results: Precision studies at 3 levels (Beckman Immage) demonstrated within-run CVs between 2.3 and 3.7%, and total CVs of 4.9– 6.4%. Assay linearity was confirmed for AAT ranging from 0.11 to 2.69 g/L (R 2 = 0.997). The assay was confirmed to be free from lipemic interference up to triglyceride levels of at least 19.85 mmol/L. Freezing and thawing of the samples did not significantly alter measured AAT. Correlation against a Behring nephelometer by least squares regression (n = 23) demonstrated a regression equation of y = 1.0179x − 0.0538 and R 2 of 0.88. The total error of our assay at a decision level of 0.5 g/L is estimated to be 0.15 g/L. Conclusions: AAT measures are not standardised across different platforms. This may affect the value chosen to initially identify those at risk for AAT deficiency, and platform-specific reference intervals may be required. Unlike urine, freezing and thawing of plasma do not affect AAT. doi:10.1016/j.clinbiochem.2011.06.028
P518 Risk managment and patient safety: Assaying for ethylene glycol — A case of mistaken identity? K. Hauff a, S. Hill a,b, J. Zeidler a,b a Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada b Hamilton Regional Laboratory Medicine Program, Hamilton, ON, Canada Objective: Ethylene glycol (EG) is converted to the toxic metabolites, glycolate and oxalate. Propylene glycol (PG) is metabolized to lactate. Although iatrogenic intoxication exists, rarely is PG ingested in levels high enough to be toxic. Of clinical importance is PG's potential for interference in gas chromatography (GC) of EG, given their similar retention times. Absolute retention times (ARTs) between runs can vary considerably, making identification difficult and requiring careful comparison to controls. We sought to investigate how often peaks in patient samples corresponded with PG versus EG, and whether there is a better method of identifying sample peaks than comparing ARTs to daily controls. Methods: EG GC chromatograms from 2009–2010 at Hamilton Regional Lab Program were reviewed and patient peak identities confirmed. ARTs were determined for EG, PG, and internal controls. Relative retention time (RRT) was calculated as a ratio of EG, or PG, ART over the internal standard ART. Results: EG was found in 7% of all samples, while 21% contained PG. No patient samples consisted of both EG and PG peaks, nor were any reported incorrectly. ARTs varied greatly over time (CVs = 2.47% EG, 2.64% PG), while RRTs were more stable (CVs = 0.94% EG and 0.85% PG). Conclusions: We determined that there is a high risk of misidentifying PG and EG. RRTs showed less variation and a clear division of EG (<0.745) from PG (>0.745) peaks. In addition to comparing ARTs, RRTs can provide greater confidence to the identification of EG peaks in patient samples. doi:10.1016/j.clinbiochem.2011.06.029
Results: Raw p-values for significant tests were adjusted using the Bonferroni method to account for any significance seen due to multiple comparisons. Fasting had significant effects on 9/38 analytes, with HDL cholesterol being the most highly affected (p = 7 × 10 − 7). Values tended to decrease post-prandially, except for uric acid which increased. By ANOVA, 24 chemistries, including triglycerides, significantly differed across times of day tested. Analysis of individual time points showed differences between morning fasting and mid-afternoon samples. Conclusions: Fasting is necessary for analysis of certain chemistries in pediatric subjects. For most tests, food intake did not influence measured values, but there was variation depending on the time of day the test was done. Pediatricians should consider diurnal factors when ordering non-fasting tests. doi:10.1016/j.clinbiochem.2011.06.026
P516 Case report: Laboratory investigation of factitious hyperkalemia in a chronic lymphocytic leukemia patient Y. Gong a,b, G. Hoag a a Dept. Laboratory Medicine, Vancouver Island Health Authority, Victoria, BC, Canada b Biochemistry Division, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada Background: Preanalytical conditions, such as hemolysis, thrombocytosis, and leukocytosis, have been known to cause factitious hyperkalemia to various degrees. Objective: To report a case of severe factitious hyperkalemia due to chronic lymphocytic leukemia (CLL) and laboratory procedures to mitigate interference due to leukocytosis. Case summary: A 63-year-old male was admitted with bilateral bronchopneumonias and end-stage CLL. His original plasma potassium in lithium heparin tube measured on Beckman Coulter UniCel DxC (DxC), was 9.4 mmol/L. Same specimen, measured on Abbott i-STAT, gave potassium >9.0 mmol/L. However, a whole blood run on GEM Premier 4000 (GEM) at bedside showed potassium at 3.8 mmol/L. Patient's WBC was at 1012 × 10 9/L. On the second day, two separate samples (collected 1.5 h apart) were measured at 10.3 and 2.3 mmol/L on DxC. To further reveal the potassium status, a sample was carefully collected in lithium heparin tube, then tube was gently inverted twice to mix anticoagulant and carried back to the lab at 37 °C for immediate analysis. Whole blood sample was run on GEM and gave a potassium value of 4.0 mmol/L. After being centrifuged at 2000 rpm for 2 minutes, plasma specimen was measured at 4.7 mmol/L on DxC. Discussion: In the case reported, factitious severe hyperkalemia was caused by extreme leukocytosis due to CLL, probably because of white blood cell fragility coupled with mechanical stress during routine sample process procedure. Conclusions: Gentle and prompt sample process ensure that laboratory potassium measurement is valid in patients with extreme leukocytosis. A whole blood sample type can also facilitate confirmation of a valid patient result. doi:10.1016/j.clinbiochem.2011.06.027
P517 Performance studies on a nephelometric assay for alpha1-antitrypsin A.M. Grunbaum a, A. Mattman b, B.M. Gilfix a a McGill University Health Centre (MUHC), Montreal QC, Canada b St. Paul's Hospital (SPH), Vancouver, BC, Canada
1171
Objectives: Alpha-1 antitrypsin (AAT) deficiency is an underrecognised inherited disorder affecting primarily the lungs and liver. In the US, only 5% of an estimated 100,000 individuals with severe deficiency have been diagnosed, most commonly due to the Z allele variant. In an effort to establish cross-Canada referral centres for the diagnosis of AAT deficiencies, we report our validation of an AAT nephelometric assay and an inter-site correlation study. Methods: Serum specimens were collected from MUHC patients according to established protocols, and frozen at −20 °C until analysis. Validation studies were performed on a Beckman Immage 800 rate nephelometer and correlated against a Behring nephelometer (SPH). Results: Precision studies at 3 levels (Beckman Immage) demonstrated within-run CVs between 2.3 and 3.7%, and total CVs of 4.9– 6.4%. Assay linearity was confirmed for AAT ranging from 0.11 to 2.69 g/L (R 2 = 0.997). The assay was confirmed to be free from lipemic interference up to triglyceride levels of at least 19.85 mmol/L. Freezing and thawing of the samples did not significantly alter measured AAT. Correlation against a Behring nephelometer by least squares regression (n = 23) demonstrated a regression equation of y = 1.0179x − 0.0538 and R 2 of 0.88. The total error of our assay at a decision level of 0.5 g/L is estimated to be 0.15 g/L. Conclusions: AAT measures are not standardised across different platforms. This may affect the value chosen to initially identify those at risk for AAT deficiency, and platform-specific reference intervals may be required. Unlike urine, freezing and thawing of plasma do not affect AAT. doi:10.1016/j.clinbiochem.2011.06.028
P518 Risk managment and patient safety: Assaying for ethylene glycol — A case of mistaken identity? K. Hauff a, S. Hill a,b, J. Zeidler a,b a Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada b Hamilton Regional Laboratory Medicine Program, Hamilton, ON, Canada Objective: Ethylene glycol (EG) is converted to the toxic metabolites, glycolate and oxalate. Propylene glycol (PG) is metabolized to lactate. Although iatrogenic intoxication exists, rarely is PG ingested in levels high enough to be toxic. Of clinical importance is PG's potential for interference in gas chromatography (GC) of EG, given their similar retention times. Absolute retention times (ARTs) between runs can vary considerably, making identification difficult and requiring careful comparison to controls. We sought to investigate how often peaks in patient samples corresponded with PG versus EG, and whether there is a better method of identifying sample peaks than comparing ARTs to daily controls. Methods: EG GC chromatograms from 2009–2010 at Hamilton Regional Lab Program were reviewed and patient peak identities confirmed. ARTs were determined for EG, PG, and internal controls. Relative retention time (RRT) was calculated as a ratio of EG, or PG, ART over the internal standard ART. Results: EG was found in 7% of all samples, while 21% contained PG. No patient samples consisted of both EG and PG peaks, nor were any reported incorrectly. ARTs varied greatly over time (CVs = 2.47% EG, 2.64% PG), while RRTs were more stable (CVs = 0.94% EG and 0.85% PG). Conclusions: We determined that there is a high risk of misidentifying PG and EG. RRTs showed less variation and a clear division of EG (<0.745) from PG (>0.745) peaks. In addition to comparing ARTs, RRTs can provide greater confidence to the identification of EG peaks in patient samples. doi:10.1016/j.clinbiochem.2011.06.029