Mary F. Burritt

Serum Cardiac Troponins and N-Terminal Pro-Brain Natriuretic Peptide: A Staging System for Primary Systemic Amyloidosis

PURPOSE Primary systemic amyloidosis (AL) is a multisystemic disorder resulting from an underlying plasma cell dyscrasia. There is no formal staging system for AL, making comparisons between studies and treatment centers difficult. Our group previously identified elevated serum cardiac troponin T (cTnT) as the most powerful predictor of overall survival. Others have reported that N-terminal pro-brain natriuretic peptide (NT-proBNP) is a valuable prognostic marker. We sought to develop a staging system for patients with AL. PATIENTS AND METHODS Two hundred forty-two patients with newly diagnosed AL who were seen at the Mayo Clinic between April 1979 and November 2000, and who had echocardiograms and stored serum samples at presentation were eligible for this retrospective review. NT-proBNP measurements were performed on 242 patients in whom cTnT and cardiac troponin I (cTnI) had been previously run. Two prognostic models were designed using threshold values of NT-proBNP and either cTnT or cTnI (NT-proBNP < 332 ng/L, cTnT < 0.035 microg/L, and cTnI < 0.1 microg/L). Depending on whether NT-proBNP and troponin levels were both low, were high for only one level, or were both high, patients were classified as stage I, II, or III, respectively. RESULTS Using the cTnT+NT-proBNP model 33%, 30%, and 37% of patients were stages I, II, and III, respectively, with median survivals of 26.4, 10.5, and 3.5 months, respectively. The alternate cTnI+NT-proBNP model predicted median survivals of 27.2, 11.1, and 4.1 months, respectively. CONCLUSION Stratification of AL patients into three stages is possible with two readily available and reproducible tests setting the stage for more consistent and reliable cross comparisons of therapeutic outcomes.

Survival in patients with primary systemic amyloidosis and raised serum cardiac troponins

Patients with primary systemic amyloidosis that affects the heart have a poor outlook. Cardiac troponins T and I (cTnT, cTnI) are highly specific and sensitive biomarkers of myocardial injury. Values of these troponins provide quantitative information about the disease. We retrospectively assessed 261 patients newly diagnosed as having primary systemic amyloidosis. Median survival for patients with detectable cTnT and cTnI (6 and 8 months, respectively), was worse than that for those with undetectable values (22 and 21 months, respectively). Median and 25th and 75th percentile values for cTnT were 0.024 microg/L, less than 0.01 microg/L, and 0.084 microg/L, and for cTnI were 0.1 microg/L, 0.05 microg/L, and 0.24 microg/L, respectively. After multivariate analysis, cTnT proved a better predictor of survival than cTnI.

Serial Biomarker Measurements in Ambulatory Patients With Chronic Heart Failure The Importance of Change Over Time

Background— Cardiac troponin T (cTnT) and B-type natriuretic peptide (BNP) have been used to estimate prognosis in heart failure; however, most studies have evaluated decompensated patients with single measurements. To determine if there are advantages to serial measurements, we evaluated stable chronic heart failure patients every 3 months for 2 years. Methods and Results— A cohort of 190 New York Heart Association class III–IV heart failure patients was prospectively enrolled from June 2001 to January 2004. Primary end points were death, cardiac transplantation, or hospitalization. At study enrollment cTnT was <0.01 ng/mL in 87 (45.8%) patients, 0.01 to 0.03 ng/mL in 50 (26.3%) patients, and >0.03 ng/mL in 53 (27.9%) patients. An increase in cTnT above normal (<0.01 ng/mL) carried a 3.4-fold increased risk (P=0.019). Further increases (≥20%) from an elevated level worsened the overall risk (hazard ratio, 5.09; P<0.001). BNP was elevated (>95th percentile for age and gender normal population) in 122 (64.2%) patients. An elevation of BNP from normal at any time during the study was associated with a poor outcome, but, once elevated, further changes in BNP (increases or decreases) remained associated with the same risk (hazard ratio, 5.09; P<0.001). Combined elevations of cTnT (>0.03 ng/mL) and BNP defined the highest risk group (hazard ratio, 8.58; P<0.001). Conclusions— Elevations of cTnT or BNP from normal detected at any time during clinical follow-up in ambulatory patients with chronic heart failure are highly associated with an increased risk of events. Further increases in cTnT contribute to additional risk. Combined elevations of cTnT and BNP contribute the highest risk. The ability to monitor changes by serial measurements adds substantially to the assessment of risk in this patient population.

Diurnal variation of serum iron, iron-binding capacity, transferrin saturation, and ferritin levels

Serum iron levels vary throughout the day. Morning levels are generally assumed to be higher than afternoon or evening levels. We studied whether our practice of restricting serum iron collections to the morning was necessary. Serum iron, iron-binding capacity, transferrin saturation, and ferritin levels were determined on blood specimens obtained from 20 healthy adult volunteers at 8 AM, noon, and 4 PM (day 1) and 8 AM (day 2). Although statistically significant differences among mean values for the collection times were observed for iron, iron-binding capacity, and (log) ferritin, no consistent diurnal variation was seen. Morning iron levels were higher than afternoon levels for only half of the subjects. Between-day variation for all 4 analytes was similar to within-day variation. We conclude that the practice of restricting iron specimen collections to a specific time of day does not improve the reliability of the test result.

Profiles of Serial Changes in Cardiac Troponin T Concentrations and Outcome in Ambulatory Patients With Chronic Heart Failure

OBJECTIVES The purpose of this study was to determine whether different profiles of cardiac troponin T (cTnT) values assessed over time would yield incremental prognostic information on clinically stable outpatients with heart failure (HF). BACKGROUND cTnT levels were used to estimate prognosis in HF; however, most studies evaluated hospitalized patients using single measurements. METHODS A cohort of 172 New York Heart Association functional class III to IV outpatients was prospectively studied with serial cTnT measurements collected every 3 months over a 2-year period. The primary end point was death or cardiac transplantation, and secondary end points included HF hospitalization. RESULTS Of the 172 patients, 22 (13%) died or underwent transplantation during the first year. Therefore, 150 patients were included in the second-year analysis of 3 pre-determined groups: 1) no serial cTnT elevations (defined as <0.01 ng/ml); 2) 1 or more, but not all cTnT values elevated > or =0.01 ng/ml; and 3) all cTnT values elevated during the first year. During the second year, 30 events occurred: 53 patients had persistently normal cTnT levels (<0.01 ng/ml) with 6 primary events (11%); 57 patients had 1 or more but not all cTnT levels elevated with 11 events (19%); 40 patients demonstrated persistently elevated cTnT levels with 13 (33%) primary events (odds ratio: 3.77; 95% confidence interval: 1.28 to 11.07, p = 0.02). CONCLUSIONS Elevations in cTnT, even using a low threshold of 0.01 ng/ml, detected during routine clinical follow-up of ambulatory patients with HF, are highly associated with an increased risk of events, particularly with frequent or persistent cTnT elevations of > or =0.01 ng/ml. Therefore, the ability to monitor clinical change through serial cTnT measurements may add to risk assessment in the ambulatory HF population.

Screening for hemochromatosis: A cost-effectiveness study based on 12,258 patients

BACKGROUND/AIMS Current emphasis in hemochromatosis has focused on early detection and treatment to prevent permanent liver damage and hepatocellular carcinoma. Thus far, only normal population and high-risk groups have been screened but not patients seeking medical care. METHODS Serum iron levels were determined in consecutive fasting blood samples collected in the morning from 12,258 Mayo Clinic patients. RESULTS One hundred twenty-seven patients had an initial serum iron concentration > or = 180 micrograms/dL. Eight patients (age, 38-71 years; 7 men and 1 woman) had transferrin saturation > or = 62% (range, 84-99) and serum ferritin value > or = 400 micrograms/L (range, 457-4004) with no other explanation for the abnormal iron test results. Three patients (2 male and 1 female) had markedly elevated hepatic iron concentration (range, 11,080-29,719 micrograms/g dry wt) and hepatic iron index (range, 2.9-8.4) indicative of homozygous hemochromatosis. One patient who refused liver biopsy had 7 g of iron removed by phlebotomy and is likely homozygous. Two patients had hepatic iron indices < 1.5 and are probably heterozygous. The genetic status of 1 patient is indeterminate, and 1 patient with normal hepatic iron concentration and hepatic iron index had chronic active hepatitis. None had cirrhosis, diabetes, or cardiomyopathy. No patients with hemochromatosis would have been detected without this study. CONCLUSIONS The yield in this study, 0.33 cases of 1000 screened, is approximately one tenth of the predicted homozygote frequency by recent estimates. Even at this yield, screening appears cost-effective.

Comparison of Lactate Values Between Point-of-Care and Central Laboratory Analyzers

Measurement of lactate levels is important in the care of critically ill adult and pediatric patients. We compared 3 whole blood lactate methods (Radiometer ABL 725, Radiometer Medical A/S, Bronshoj, Denmark; i-STAT, i-STAT, East Windsor, NJ; and Nova Lactate Plus, Nova Biomedical, Waltham, MA) with 2 plasma-based methods (Roche Integra, Roche Diagnostics, Indianapolis, IN; and Vitros, Ortho Clinical Diagnostics, Rochester, NY). The Vitros LAC slide assay was used as the reference method. Results were compared by least squares regression and Bland-Altmann plots and by comparing concordance within clinically relevant lactate ranges. Correlation between lactate methods was good with slopes between 0.87 and 1.06 and intercepts of 0.9 to 1.8 mg/dL (0.1-0.2 mmol/L) of lactate for all 4 methods compared with the Vitros. At high (>54.1 mg/dL [6 mmol/L]) lactate values, the Radiometer and i-STAT methods reported lower lactate results compared with the Vitros and Integra. The Nova analyzer reported higher lactate results than either the Vitros or Integra. The negative bias in i-STAT and Radiometer results may confound the interpretation of patient condition if multiple methods are used within the same institution.

The determination of mercury in whole blood and urine by inductively coupled plasma mass spectrometry

Abstract An inductively coupled mass spectrometric (ICP-MS) method for the determination of mercury in whole blood and urine was developed. Gold and dichromate in hydrochloric acid were evaluated as agents to reduce mercury spray chamber memory. Dichromate with hydrochloric acid was found to be superior to gold. We evaluated the rapid introduction of sample to promote equilibrium and the rapid introduction of wash solutions after the sample analyses to minimize mercury memory. This ‘fast pump’ mode (2.5 ml/min) was used for 20 s at the beginning and end of each sample-wash cycle. The mercury detection limit is 0.15 μg/l in the original sample before dilution. Regressions and correlation coefficients for ICP-MS vs. target concentrations for interlaboratory comparison samples from the Centre de Toxicologie du Quebec were: whole blood: y=1.0x−0.6; r=0.9801; n=27 and urine: y=0.84x+8; r=0.9915; n=42. Patient samples were analyzed by ICP-MS and cold vapor atomic absorption spectrometry (CVAAS). Regressions and correlations for patient samples were: urines: y=0.93x+1; r=0.8763; n=456 and whole blood: y=1.1x+0.2; r=0.9357; n=251. ICP-MS correlation with CVAAS for 29 urine samples containing 15–150 μg Hg/specimen was: y=0.94x+4; r=0.9864.

Pediatric Reference Intervals for 19 Biologic Variables in Healthy Children

We defined age- and sex-specific reference intervals for 19 biologic variables in serum samples from healthy children, 1 to 22 years of age, using common laboratory equipment. Upper and lower reference intervals were defined as the estimated 2.5 and 97.5 percentiles of the distribution. For variables (y) that varied with age, the relationship of y to age was modeled with polynomial regression. Parametric percentile estimates specific to each age were then calculated as the predicted y value +/- 1.96 . SD, in which SD = the standard deviation of the residuals. For variables not associated with age, the nonparametric 2.5 and 97.5 sample percentiles were used to define the reference intervals. No significant age or sex differences were found for serum sodium, total protein, glucose, direct bilirubin, or albumin. Potassium, chloride, and urea showed constant values in children that were higher than adult values in the case of potassium and chloride and lower than adult values in the case of urea. No sex-related differences were seen for these analytes. Creatinine, uric acid, and bicarbonate showed an upward trend in values with increasing age, whereas aspartate aminotransferase, phosphorus, and total and ionized calcium showed a downward trend with increasing age. Sex-related differences were noted for these analytes. The immunoglobulins (IgG, IgA, and IgM) showed an upward trend with increasing age, with no sex-related differences except for IgM in children.

Macroenzyme as a Cause of Unexplained Elevation of Aspartate Aminotransferase

Aspartate aminotransferase (AST) can exist as a macroenzyme by forming a complex with an immunoglobulin. This immunoglobulin-complexed macromolecule can cause an elevation in serum AST activity, which may be detected on routine blood chemistry analysis and erroneously considered to indicate the presence of liver disease. Clinicians should be aware of this phenomenon so patients are not subjected to unnecessary procedures. In patients with unexplained AST elevation, liver and muscle disease can be biochemically excluded by the finding of normal serum levels of alanine aminotransferase and creatine kinase. The presence of macro-AST can be determined by exclusion chromatography, electrophoresis, and activation assays with pyridoxal 5-phosphate. The elevated AST values can persist for many years.