Low sensitivity of anion gap to detect clinically significant lactic acidosis in the emergency department.

INTRODUCTION: Lactic acidosis represents the pathologic accumulation of lactate and hydrogen ions. It is important to efficiently diagnose lactic acidosis as delayed treatment will lead to poor patient outcomes. As plasma lactate levels may not be rapidly available, some physicians may use elevated anion gaps to test for the need to measure lactate. All Edmonton metropolitan hospitals have Radiometer blood gas/electrolyte instruments in the ED or close by. As lactate is measured for each set of electrolytes, we were able to determine the effectiveness of a screening anion gap for lactic acidosis. METHODS: Two years of emergency department lactates and electrolytes from Edmonton's 5 metropolitan hospitals were analyzed. We determined the sensitivity, specificity and positive predictive value of detecting an elevated lactate, defined as ≥2.5mmol/L or ≥4mmol/L. RESULTS: Depending on the elevated anion gap cut-off and the definition of elevated lactate, between 40-80% of elevated lactates are missed. In general, the positive predictive value approaches 40% for AGs ≥12mmol/L and 60% for AGs ≥16mmol/L. CONCLUSIONS: Anion gap is an inadequate marker of lactic acidosis. We recommend that lactate be done with each set of electrolytes and/or blood gases. In this way lactic acidosis will not be missed.

The use of serial outpatient complete blood count (CBC) results to derive biologic variation: a new tool to gauge the acceptability of hematology testing.

INTRODUCTION: Most estimates of biologic variation (sb ) are based on periodically acquiring and storing specimens from reference subjects, followed by analysis within a tightly controlled analytic run. We demonstrate that reliable estimates of sb can be derived for virtually all constituents of the CBC from previously obtained paired patient results and summary QC data. METHODS: A laboratory data repository provided all of the outpatient CBC results measured over 20.5 months at a large Canadian referral laboratory. These CBC measurements were taken on one of four Beckman Coulter LH analyzers. A total of 1852 different patients had CBCs repeated at least twice within 84 h. We tabulated the pairs of intrapatient constituents that were separated by 0-6, 6-12, 12-18,… 72-78, and 78-84 h. The standard deviations of duplicates (SDD) of the paired data were then regressed against time. The y-intercept represents the sum of sb and short-term analytic variation (sa ): y0 =(s(2) a +s(2) b )(1/2) . The short-term imprecision was determined from normal range Coulter quality control specimens. RESULTS: Patient sb for hematocrit, MCH, absolute monocytes, and absolute neutrophils are extremely close to those determined by biologic variation experiments using healthy volunteers. Most of the other estimates of sb tended to be slightly lower than literature estimates. CONCLUSIONS: We describe a novel approach to deriving sb . The ratio of the sb to sa (a measure of sigma) indicates that the Beckman Coulter LH is extremely suitable for CBC monitoring of outpatients as well as for inpatients, whose sb is generally higher.

The prediction of postoperative stroke or death in patients with preoperative atrial fibrillation undergoing non-cardiac surgery: a VISION sub-study.

BACKGROUND: The optimal means of pre-operative risk stratification in patients with atrial fibrillation (AF) is uncertain. OBJECTIVE: To examine the accuracy of AF thromboembolic risk models (the CHADS2, CHA2DS2-VASc, and R2CHADS2 scores) for predicting 30-day stroke and/or all-cause mortality after non-cardiac surgery in patients with preoperative AF, and to compare these risk scores with the Revised Cardiac Risk Index (RCRI). PATIENTS/METHODS: A multicentre (8 countries, 2007-2011) prospective cohort study of patients ≥ 45 years of age undergoing inpatient non-cardiac surgery, who were followed until 30 days after surgery. We calculated c-statistics for each risk prediction model and net reclassification improvements (NRIs) compared with the RCRI. RESULTS: The 961 patients with preoperative AF were at higher risk of any cardiovascular event in the 30 days postoperatively compared with the 13 001 patients without AF: 26.6% vs. 9.0%; adjusted odds ratio, 1.58; 95% confidence interval [CI], 1.33-1.88. All thromboembolic risk scores predicted postoperative death just as well as the RCRI (with c-indices between 0.67 and 0.72). Compared with the RCRI (which had a c-index of 0.64 for 30-day stroke/death), the CHADS2 (c-index, 0.67; NRI, 0.31; 95% CI, 0.02-0.61) significantly improved postoperative stroke/mortality risk prediction, largely due to improved discrimination of patients who did not subsequently have an event. CONCLUSIONS: In AF patients, the three thromboembolic risk scores performed similarly to the RCRI in predicting death within 30 days and the CHADS2 score was the best predictor of postoperative stroke/death regardless of type of surgery.

Postanalytical quality improvement: a College of American Pathologists Q-Probes study of elevated calcium results in 525 institutions.

OBJECTIVE: To evaluate elevated patient calcium results as a postanalytic quality indicator of physician practices. DESIGN: Participants prospectively identified hypercalcemic patient results for 4 months or until they found 320 hypercalcemic results, and then, after at least 3 days, reviewed the medical records of these patients. Hypercalcemia was defined as a calcium value that exceeded the upper limit of each laboratory's reference range by 0.12 mmol/L or more. Participants, as well a subset of their physicians who did not acknowledge or respond to elevated results in the medical record, answered a questionnaire about their practices. PARTICIPANTS: Five hundred twenty-five laboratories enrolled in the College of American Pathologists Q-Probes program. MAIN OUTCOME MEASURES: The presence of hyercalcemic results in patients' medical records and physicians' acknowledgement and response to those elevated results. RESULTS: More than 5500 hypercalcemic results were identified, of which 53.2% represented a new finding. About 3.5% of results were not charted in the patients' records, and 23.1% of patient records did not contain clinician documentation of the abnormal result. Follow-up laboratory tests were not ordered for 13.8% of the elevated values. For 570 of the 808 results for which there was neither clinician documentation nor designated follow-up laboratory tests ordered, patients' physicians received written notification of the elevated calcium results along with a questionnaire. Responses were received from 386 physicians (68%). One hundred physicians indicated they did not order the specific calcium measurement, and of these 100, 85 responded it was part of a panel. The 286 physicians who ordered the test stated the results ultimately led to further testing (69%), a change of management (56%), or a new diagnosis (25%). CONCLUSIONS: We found that a high percentage of abnormal results (3.5%) were not documented in the patients' medical records, the diagnosis of hypercalcemia frequently was new (53.2%), and a high percentage of physicians did not respond to elevated calcium results by writing a note (23.1%) or ordering another test (13.8%). Opportunities for quality improvement at these postanalytical steps are far greater than at the analytical step. Laboratorians must help physicians identify and respond to clinically important laboratory results.

Identifying variables associated with inaccurate self-monitoring of blood glucose: proposed guidelines to improve accuracy.

PURPOSE: This study was conducted to evaluate patients' proficiency in self-monitoring of blood glucose (SMBG). METHODS: Diabetes nurse educators in 4 suburban Minneapolis clinic sites surveyed the SMBG training/cure practices of 280 patients with type 1 and type 2 diabetes. Participant SMBG technique was measured by direct observation. Participants performed a finger puncture and used their own meters to measure the first blood sample. A second sample was measured on the HemoCue B Glucose analyzer, and a third sample was used to measure hemoglobin. The series of tests were then repeated. If either of the 2 glucose tests was more than 15% from the HemoCue value, participants were reeducated about the manufacturer's suggested procedure. RESULTS: Of the 280 participants, 19% had blood glucose test results greater than the 15% limit for meter accuracy. After reeducation, 69% of those who had initially failed achieved acceptable results. The most significant problems were lack of periodic meter technique evaluation, difficulty using wipe meters, incorrect use of control solutions, lack of hand washing even when observed, and unclean meters. CONCLUSIONS: As a result of the study, guidelines were subsequently developed to evaluate meter accuracy in an outpatient setting. Further effort is needed to establish standards for evaluating SMBG.

Laboratory restructuring in metropolitan Edmonton: a model for laboratory reorganization in Canada.

In 1994 the Alberta government acted to reduce to a decade-long deficit in the provincial budget with draconian reductions in the health, education and welfare expenditures. As a result, funding to Alberta clinical laboratories was to be reduced by approximately 40%. In response, the private and public laboratories in metropolitan Edmonton formed a unique alliance to provide laboratory testing in a more coordinated and efficient manner. Of the five metropolitan hospitals, only University of Alberta Hospital preserved its full service laboratory and its specialty reference testing. The other hospital laboratories were converted to rapid response laboratories with a merged private reference laboratory providing routine testing and support to the four hospitals, and far fewer outpatient collection facilities. This paper describes the steps in the laboratory restructuring from inception to execution.

Thoughts on quality-control systems: a laboratorian's perspective.

State-of-the-art prospective quality-control systems entail the use of medically relevant, analyte-specific quality control limits. With analyte-specific limits broader than those generally used in the clinical laboratory, there will be fewer false rejections, fewer unnecessary reanalyses, and shorter delays in run reporting. If the analyte-specific limits are narrower than those used in the laboratory, more errors will be detected, but the user is at risk of identifying errors over which s/he and the manufacturer have little control. The use of various patient data quality-control algorithms is described. Conservatism is stressed in adopting manufacturers' guidelines for surrogate, nondestructive quality-control testing. A simple, optimized approach is suggested for the systematic retrospective review of proficiency data. Finally, an approach is presented for converting from older, previously accepted quality control procedures to more efficient analyte-specific quality control.

Patient and physician analytic goals for self-monitoring blood glucose instruments.

The study's objective was to determine the maximum analytical error that is allowable in portable whole blood glucose meters. Interviews were conducted to derive personal reference values and significant deviations from these values for the limit of hypoglycemia, the limit of hyperglycemia, and the upper and lower limits of acceptable blood glucose for physicians and patients with diabetes at the Park Nicollet Medical Center, Minneapolis, Minnesota. Fifty patients with diabetes (30 type I and 20 type II), and 43 physicians (14 endocrinologists, 14 family practitioners, and 15 general internists) were enrolled in the study. The results showed no significant differences between type I and type II diabetic patient responses. Nor were there significant differences among family practitioner, internist, and endocrinologist responses for any of the parameters (the limit of hypoglycemia, the limit of hyperglycemia, the upper and lower limits of acceptable blood glucose for the patient, and the corresponding allowable coefficients of variation at each of these glucose levels). There were significant differences when patients were compared to physicians. Physicians require the highest degree of precision at the limit of hyperglycemia (8.4 +/- 0.28 mmol/L [150.8 +/- 5.1 mg/dL]) with a maximum allowable coefficient of variation (CV) of 7%, a CV significantly lower than that of the patients (CV = 10%). Patients require the highest precision for glucose concentration around the lower acceptable limit (4.7 +/- .013 mmol/L [84.1 +/- 2.5 mg/dL]), with an allowable CV of 8%, a CV significantly lower than that of the physicians (CV = 14%). The authors conclude that the accuracy required by patients and physicians at normal and higher glucose concentrations is achievable by currently available meters. Manufacturers should ascertain that glucose measurements are optimally accurate at glucose levels of 4.7 mmol/L (84.1 mg/dL) and have CVs no higher than 7%.