Hemodynamic and metabolic responses to exercise after alpha 1-, beta 1-, and nonselective beta-adrenoceptor blockade in man.

The effects of acute alpha 1-adrenoceptor blockade with prazosin, beta 1-adrenoceptor blockade with atenolol, and nonselective beta-adrenoceptor blockade with propranolol were compared in a placebo-controlled crossover study. The study involved measurement of the hemodynamic and metabolic responses to exercise after heavy exercise in order to induce skeletal muscle glycogen depletion and thus enhance the dependence on hepatic glucose output and circulating free fatty acids. Catecholamine responses to exercise were enhanced by glycogen depletion and by both beta-blocking drugs. Catecholamine levels were highest with propranolol; as a consequence, at high work loads, propranolol failed to produce a significant reduction in systolic blood pressure and elevated diastolic blood pressure. At high work loads, atenolol reduced systolic blood pressure but did not change diastolic blood pressure. Both beta blockers reduced free fatty acid levels, but only propranolol accelerated the fall of plasma glucose levels during "glycogen-depleted" exercise. In contrast, during exercise prazosin reduced systolic and diastolic blood pressures, and elevated heart rate and plasma catecholamines, particularly noradrenaline. Concomitantly, prazosin raised free fatty acid and lactate levels, and increased the plasma glucose level at a time when placebo therapy resulted in a steady fall in glucose levels. The results indicate important differences in the hemodynamic effects of cardioselective versus nonselective beta-blockade during long-term (or glycogen-depleted) exercise. The importance of beta 2-mediated hepatic glycogenolysis in man is confirmed. Acute alpha 1-blockade with prazosin induces reflex elevation of catecholamine levels. There is no indication of an important role for an alpha 1-mediated mechanism in hepatic glucose production in man.

Breast milk iodide: reassessment in the 1980s.

In addition to iodized salt, the American diet is inadvertently supplemented with iodine from other foods, such as bread and cow's milk. The iodine content of breast milk has not been assessed recently in this country. Sixty-one samples of breast milk from 37 women were analyzed for iodide content using an iodide-selective electrode method. Mean breast milk iodide level on initial samples for this population was 178 micrograms/L (range 29 to 490 micrograms/L), about four times the recommended daily allowance for infants. Iodide levels in breast milk did not correlate with the age of the infant (ie, stage of lactation). There was a significant correlation between the iodide level in the breast milk and dietary iodine as estimated by a food frequency questionnaire, and iodized salt intake was significantly related to the iodide content of the breast milk.

Nomogram for estimating creatinine clearance.

Several methods have been published for estimating creatinine clearance from serum creatinine concentrations. Such estimates of creatinine clearance are widely used for dosage adjustments of drugs which are primarily eliminated through the kidneys in patients with reduced renal function. Most of these methods involve the use of equations, requiring a few steps of calculations. A simple and easy-to-use nomogram is presented for estimating creatinine clearance from serum creatinine concentration, plus the age, sex, and bodyweight of the individual patient. This nomogram is based on the linear relationship between creatinine clearance and the reciprocal value of the serum creatinine concentration, where the slope of this relationship is determined by the rate of creatinine production. The rate of creatinine production, however, is related to age, sex, and bodyweight. These physical characteristics are therefore used to scale the slopes of the relationships between creatinine clearance and serum creatinine concentration. The validity of the nomogram was tested in 50 consecutive hospitalised patients for which creatinine clearance was measured. There was an excellent correlation (r = 0.903) between predicted and observed creatinine clearance values.

Comparison of cardiac troponin T versus creatine kinase-MB for risk stratification in a chest pain evaluation unit.

We evaluated cardiac troponin T (cTnT) and creatine kinase-MB (CK-MB) for risk stratification of chest pain unit (CPU) patients. We studied 383 consecutive patients with chest pain assigned to our CPU by emergency department physicians. At baseline all had normal or nondiagnostic electrocardiograms, no high-risk clinical features, and negative CK/CK-MB. CK-MB and electrocardiograms were taken at 0, 4, 8, and 12 hours and cTnT at 0, 4, and 8 hours. Eight patients (2.1%) were CK-MB positive and 39 (10.2%) were cTnT positive, including all but 1 CK-MB-positive patient. All marker-positive patients were detected by 8 hours. Seven cTnT-positive patients and 1 cTnT-negative patient had myocardial infarction (p <0.0001). cTnT-positive patients were older, less likely to be women or smokers, and more often had diabetes mellitus or known coronary disease (CAD). Seventy-one percent of patients underwent diagnostic testing. cTnT-positive patients more often underwent angiography (46% vs 20%) and underwent stress testing less often (28% vs 57%) than cTnT-negative patients. When performed, their stress tests were more often positive (46% vs 14%) and they more often had angiographically significant lesions (89% vs 49%) and multivessel disease (67% vs 29%). There were no short-term deaths. Long-term mortality was higher in cTnT-positive patients (27% vs 7%, p <0.0001). Thus, cTnT identified more CPU patients with myocardial necrosis and multivessel CAD than CK-MB and a population with high long-term mortality risk. Routine use of cTnT in CPUs could facilitate risk stratification and management.

Laboratory tests in evaluation of acute febrile illness in pediatric emergency room patients.

The rising costs of health care and the movement for health care reform have focused attention on methods of cost containment. Of routine laboratory and radiologic procedures, complete blood cell count (CBC) and determination of serum electrolyte values rank as high as 2nd and 9th in overall cost. We retrospectively studied use of the clinical laboratory to aid diagnosis of an acute infectious event in a pediatric emergency department population. For 5 months, we reviewed medical records of pediatric patients younger than 15 years brought to the emergency department because of a febrile episode. Of 155 cases reviewed, electrolyte concentrations were determined in 108 patients and CBC in 155. In all patients, either culture or rapid test for streptococcal organisms was performed. In addition, 838 pediatric patients with similar symptoms but who did not undergo laboratory testing were monitored for 100 days. Measures of effectiveness including sensitivity, specificity, positive and negative predictive values, and likelihood ratio were used to correlate specific laboratory findings with antibiotic therapy, serious bacterial disease, and culture positivity. Electrolyte abnormalities were found largely to be dismissed clinically, with the major clinical response consisting of parental education about hydration. The CBC profile was evaluated, with white blood cell count (WBC) indicator limits of > 10,000, > 10,000 but < 15,000, and > 15,000/mm3, and differentiated into absolute neutrophil count, neutrophil percent, and band cell percent. Temperature was evaluated as an independent variable. Insofar as serious bacterial disease and culture positivity, sensitivity was uniformly low (70%), and specificity was only marginably acceptable for WBC > 15,000 (77%). Both positive predictive values and likelihood ratio were low with respect to predicting either serious bacterial disease or culture positivity, emphasizing the limited usefulness of these clinical laboratory measurements. The best hematologic predictors of serious bacterial disease or culture positivity were obtained with automated hematologic analyzers and exceeded manual differential measurement of neutrophil percent and band cell percent. In addition, we correlated the administration of antibiotics with the various hematologic parameters and discovered that WBC > 15,000, regardless of cause, almost uniformly resulted in treatment (positive predictive value, 93.5%; likelihood ratio, 5.60). These findings support the use of automated hematology analyzer-derived measurements and question the use of manual differential counts, unless specific issues are to be addressed. Furthermore, the findings seem to support more reliance on clinical impression and less on laboratory values.

Adaptation of a quantitative immunoassay for urine myoglobin. Predictor in detecting renal dysfunction.

Myoglobinuria, subsequent to rhabdomyolysis, may cause acute renal failure. For this reason, many qualitative and quantitative tests have been developed for the detection of myoglobin in urine. The authors describe the adaptation and optimization of the Stratus II serum myoglobin immunoassay to quantify urine myoglobin. In addition, the assay was used to accurately determine urine myoglobin concentrations in subjects at potential risk for myoglobin-induced renal dysfunction and the results obtained compared to conventional qualitative methods for urine myoglobin. The assay demonstrated with-in run and between-run coefficient of variations (CVs) of 6.2% and 7.2%, respectively, was linear from 0-950 micrograms/L, demonstrated good recovery, and was free from interference by hemoglobin, creatinine, and urea. Specimens were diluted with 0.1 mol/L phosphate buffer, pH 9.0 containing 3% bovine serum albumin before analysis. Myoglobin was assayed on urine obtained from 30 patients suspected of having myoglobinuria. Fifteen of 17 patients with serum creatinine greater than 1.4 mg/dL had myoglobin concentrations greater than 20,000 micrograms/L, whereas the remaining 31 patients with normal serum creatinine had urine myoglobin concentrations of less than 18,000 micrograms/L. If serum creatinine is used as an indicator of renal function, it would appear that accurate measurement of urine myoglobin may facilitate identification of patients with increased susceptibility to myoglobin-induced acute renal failure.

Urinary interleukin-8 with asymptomatic bacteriuria in pregnancy.

OBJECTIVE: To evaluate urinary interleukin-8 (IL-8), an inflammatory cytokine, as a screening method for detecting asymptomatic bacteriuria in pregnancy. METHODS: Clean-catch urine samples from 200 pregnant women undergoing screening for asymptomatic bacteriuria were evaluated by urine culture, urine dipstick analysis, and measurement of IL-8. Interleukin-8 levels were measured by a chemiluminescent immunoassay (Immulite IL-8, Diagnostic Products Corp., Los Angeles, CA), and a receiver operating characteristic curve was used to determine the optimal cutoff point. Asymptomatic bacteriuria was defined as at least 100,000 colony-forming units of a single organism per mL. Dipstick testing included nitrite assessment as positive or negative and leukocyte esterase as negative, trace, 1+, 2+, or 3+. Dipstick testing was considered positive if nitrite was positive or leukocyte esterase was trace or greater. Sensitivities, specificities, positive and negative predictive values were determined for urinary leukocyte esterase and nitrite and compared with those of IL-8. chi(2) and Mann-Whitney U tests were used for statistical analyses. RESULTS: Twenty women were identified with asymptomatic bacteriuria by urine culture. The median urinary IL-8 levels for women with and without asymptomatic bacteriuria were 356 pg/mL and 125 pg/mL, respectively (P <.01, Mann-Whitney U test). Using an optimal cutoff point of 264 pg/mL, IL-8 had a sensitivity, specificity, positive and negative predictive value of 70%, 67%, 19%, and 95% for predicting asymptomatic bacteriuria. Urine dipstick analysis with either a positive leukocyte esterase or nitrite had a sensitivity, specificity, positive and negative predictive value of 45%, 62%, 12%, and 91%, respectively, for detecting asymptomatic bacteriuria. The differences between these testing methods were not statistically significant. CONCLUSION: Urinary interleukin-8 is not an acceptable screening method for asymptomatic bacteriuria in pregnancy because it fails to detect 30% of women with this condition.

Effect of coffee on cholesterol and apolipoproteins, corroborated by caffeine levels.

The possibility that coffee may increase cholesterol levels has created uncertainty among physicians. The confusion arose from cross-sectional studies, in which female coffee drinkers appeared to show a positive association more frequently than men. To clarify this relationship, we designed an intervention trial to reduce caffeine and coffee intake sequentially while measuring total cholesterol and the apolipoprotein A-I and B levels. We conducted the study among women who were coffee drinkers (n = 35) or not coffee drinkers (n = 28). The trial spanned seven months with caffeine-free and coffee-free intervals. Serum caffeine levels corroborated compliance with the dietary protocol. Analysis of the apolipoprotein levels confirms the absence of any influence of coffee on lipoproteins in normocholesterolemic persons. We observed no apparent causal association of coffee or caffeine consumption and cholesterol and apolipoproteins.

Evaluation of the YSI 2300 glucose analyzer: algorithm-corrected results are accurate and specific.

OBJECTIVES: To insure commutability (equivalence) between whole blood and plasma glucose values and to assess potential interferences in glucose oxidase methods. DESIGN AND METHODS: We compared plasma glucose results by the Ektachem 700 analyzer to glucose results on whole blood by the Nova Stat Profile 6, and by the YSI 2300, both without hematocrit correction (YSIunc) and with two different hematocrit (Hct) corrections. The two correction methods were: (a) whole blood results multiplied by 1.11 (YSI1.11), and (b) whole blood results corrected for Hct with the programmed YSI algorithm (YSIcor). Several compounds were tested for interference. RESULTS: 88% of YSIcor results agreed with plasma results within plus/minus 5%, and 78% of Nova and 74% of YSI1.11 results were within this limit. YSIcor results were unaffected by Hct and were valid even when erythrocyte size was abnormal. At low Hct, Nova results were falsely decreased, while YSI1.11 results were falsely elevated. The Ektachem was most affected by ascorbic acid, and the Nova was especially affected by acetaminophen. CONCLUSIONS: The YSI algorithm-corrected whole blood glucose results were commutable with plasma results and the YSI was unaffected by the compounds tested, including acetaminophen and acetylsalicylic acid.

Comparison of pyridoxal phosphate-supplemented reagent kits for alanine aminotransferase using centrifugal analysis.

The addition of pyridoxal-5-phosphate for assay of alanine aminotransferase has been recommended. The referral methods are inconvenient for high volume instrumentation due to use of multiple reagents and blanks. We adapted a well-documented method to the centrifugal analyzer as a reference for adaptation of two kit methods. Reference intervals obtained and linearity determined were all similar. The kit methods compared favorably to the referral method. Linear regression analysis yielded the following: DOW = 1.011 BERG + 1.666, r = 0.9965; SKI = 0.938 BERG + 4.559, r = 0.9926; and DSKI = 1.028 BERG + 1.051, r = 0.9889. Precision of the assays was acceptable. We concluded that automation of reagent kits incorporating pyridoxal-5-phosphate is feasible and the assays compared favorably to a recommended method. High volume instrumentation can be used without denigration of analytical quality and to allow comparability to a documented method for interlaboratory review.

Effect of water rinsing on sodium content of selected foods.

The sodium content of water-rinsed canned green beans, tuna, and cottage cheese was analyzed. A 3-minute rinse of tuna and cottage cheese resulted in sodium reductions of 80% and 63%, respectively, with no significant effect on iron content. Calcium was reduced by approximately 50%. Although rinsing had a minimal effect on the sodium in canned beans, replacing the canning brine with water before heating lowered salt content by 33%. This study shows that the simple and economical methods of water rinsing of tuna and cottage cheese and of heating green beans in tap water markedly lowered salt content.

Artifactual hypoglycemia associated with hematopoietic cytokines.

We observed apparent hypoglycemia in seven patients manifesting granulocytosis associated with hematopoietic cytokine treatment or with a leukemoid reaction. All seven patients had confounding preanalytic conditions of specimen transport delay and lack of antiglycolytic agents. Cytokine-stimulated leukocytes may cause artifactual hypoglycemia by consuming glucose in vitro, possibly leading to unnecessary diagnostic evaluation. The glucose depletion was faster in blood drawn from patients receiving granulocyte colony-stimulating factor (0.29 mmol/L/h) than in blood from a control group (0.17 mmol/L/h) or from a group with leukemia (0.23 mmol/L/h). Stabilization with sodium fluoride (60 mmol/L) slowed the glucose depletion in both the cytokine group (0.13 mmol/L/h) and the leukemic group (0.09 mmol/L/h), which were then statistically indistinguishable from the control rate (0.10 mmol/L/h). In blood obtained from patients being treated with hematopoietic cytokines or who have leukemoid reactions, an antiglycolytic agent should be used whenever separation of plasma might be delayed more than 1 hour.

Pneumatic transport exacerbates interference of room air contamination in blood gas samples.

OBJECTIVE: To characterize and control the potential interference to P(O2) determinations when blood contaminated with air is sent via a pneumatic tube system (PTS). DESIGN: Both tonometered blood at P(O2)s of 65, 75, 142, and 339 mm Hg and arterial blood gas samples from patients with baseline P(O2)s from 70 to 400 mm Hg were analyzed for P(O2) to determine possible effects of air contamination from PTS transport. SETTING: A large teaching hospital in which a variety of personnel routinely send samples to the laboratory by PTS transport. PATIENTS: Twenty patients under anesthesia for elective surgery and 21 patients in an intensive care unit who had a wide range of P(O2)s. Several additional patients with a preexisting lung pathology likely to cause hypoxemia were selected to provide samples with low P(O2)s. MAIN OUTCOME MEASURES: Measurement of bias in P(O2) between samples sent via PTS and samples walked to the laboratory. RESULTS: Interference from air contamination was worse after PTS transport compared with manual transport of the specimen. Over a wide range, the P(O2) in specimens after PTS transport tended toward 160 mm Hg. Samples from hypoxemic patients were prone to errors in P(O2) that could have resulted in clinical misinterpretation; 5 of 10 samples with a baseline P(O2) less than 85 mm Hg had increases of 10 mm Hg or more when contaminated with air. Cooling samples with high P(O2)s minimized changes to P(O2), probably by increasing the solubility of oxygen. Mechanical buffering by various liners used in the carriers did little to alleviate the interference. Decreasing the speed of pneumatic transport by 50% lessened the effect on P(O2). CONCLUSION: Interference can be minimized by carefully purging samples of all air bubbles using the following protocol: invert syringe to check for air bubbles, then retap and reexpel bubbles if necessary. Personnel that collect and send blood gas samples via PTS should be educated about the problem of interference. Modifications both to pneumatic sample transport systems and to blood gas syringes should be investigated to minimize the effect.

Stability of plasma lactate in vitro in the presence of antiglycolytic agents.

The use of plasma lactate to assess metabolic or circulatory impairment requires definition of critical preanalytical and analytical parameters. Stability has been documented for only 15 min after acquisition when samples were collected with fluoride and transported on ice. We examined time elapsed before analysis, storage temperature, and the antiglycolytic agent used to define preanalytical conditions. Plasma lactate was measured with a Kodak Ektachem 700XR analyzer. In controlled studies on volunteers, storage on ice slowed but did not eliminate the production of lactate; for samples collected with sodium fluoride (F) and potassium oxalate (OX), lactate increased by 0.2 mmol/L after 1 h, then changed little regardless of the storage temperature. For patients' samples collected in F/OX, the mean increase was only 0.15 mmol/L after 24 h. Samples with leukocytosis (neutrophil counts 23 x 10(9)-52 x 10(9)/L) were also stable, with a mean increase of 0.3 mmol/L at 8 h. Use of the antiglycolytic agents F and OX (at 60 and 12 mmol/L, respectively) maintained apparently stable lactate concentrations at room temperature for up to 8 h without special handling.

Unpredictable fluctuations in serum acid phosphatase activity in prostatic cancer.

Repeated determinations of the elevated serum acid phosphatase activities in five patients with advanced prostatic cancer were found to be highly variable during 24 to 48 hours of observation. Samples collected every three hours had fluctuations of 44% to 97% around the 24- to 48-hour mean values. These fluctuations appeared to be random, had no apparent circadian rhythm, and were unrelated to concurrent medications or activity. These spontaneous variations indicate the need for caution when using serial serum acid phosphatase determinations as an indicator of the response of prostate cancer to therapy. Elevated serum alkaline phosphatase activities did not show these extreme fluctuations.

Ultrafiltration discrepancies in recovery of myoglobin from urine.

We investigated the efficiency, accuracy, and reliability of the ultrafiltration/dipstick methodology commonly used to diagnose myoglobinuria. Twenty-five myoglobin-containing urine specimens were filtered by centrifugation for 15 min at 1500g through a Centricon-30 membrane filter. Both the original specimen and filtrate were assayed for myoglobin. The amount of myoglobin recovered subsequent to filtration varied from <1-38%. This poor and variable recovery was independent of sample matrix or precentrifugation of the specimens. This was most critical for urine specimens with myoglobin concentrations <60 000 microg/L. Fourteen of 18 such filtrates had concentrations <350 microg/L, a concentration below which a negative result would be obtained by using conventional dipstick methods. Thus, the use of this procedure has the potential to misdiagnose patients with myoglobin concentrations associated with increased risk of subsequent renal dysfunction, in particular when urine myoglobin concentrations are <60 000 microg/L.

Digoxin-like immunoreactivity eliminated from serum by centrifugal ultrafiltration before fluorescence polarization immunoassay of digoxin.

Digoxin determined in the Abbott "TDx" by fluorescence polarization immunoassay by the manufacturer's recommended method involving precipitation of protein with 5-sulfosalicylic acid (SSA) is subject to interference from endogenous compounds having digoxin-like immunoreactivity. Guided by the work of Graves et al. (Clin Chem 1986;32:1506-9), we eliminated interference caused by digoxin-like immunoreactivity by substituting ultrafiltration for precipitation with SSA to remove protein. Using the manufacturer's method, we quantified digoxin in serum from 53 patients in three clinically defined groups who were receiving no digoxin, finding apparent digoxin in excess of the 200 ng/L detection limit in 24% of the 17 pregnant women, 59% of the 17 renal-dialysis patients, and all of 19 neonatal cord-blood samples examined. No measurable digoxin immunoreactivity was observed by fluorescence polarization immunoassay for any of the 53 clinically defined patients after removal of protein by ultrafiltration. For 22 men for whom digoxin was prescribed, digoxin measurement after protein removal by SSA and by ultrafiltration correlated well (r = 0.98), with good proportionality (slope = 1.04). Analytical recovery of added digoxin from adulterated serum was 115% after SSA, but 100% after ultrafiltration. Thus, before this assay procedure, we recommend ultrafiltration, to remove digoxin-like interference.

Reflotron cholesterol measurement evaluated as a screening technique.

We evaluated the analytical performance of Boehringer Mannheim Diagnostics' "Reflotron" analyzer for the measurement of cholesterol. Coefficients of variation (CVs) for whole-blood cholesterol were: within-day 2.0% and 2.2% at 1680 and 2670 mg/L, respectively; between-day 1.8% and 2.4% (n = 9 and 8). Results were similar for serum and heparinized or EDTA-treated single-donor plasma (CV 1.4% to 2.6%). CVs of results for two reconstituted commercial quality-control materials were 3.4% and 4.6%. Heparin and hematocrit were evaluated as interferents, and critical limits for interference were identified for bilirubin, hemoglobin, and triglyceride in blood and plasma or serum. When sample collection and analysis were controlled by trained personnel, results with the Reflotron (y) compared well with those by the Ektachem procedure (x) for both blood and serum samples: r = 0.950, y = 0.944x + 130 mg/L; and r = 0.955, y = 0.93x + 43.5 mg/L, respectively. The same comparability was observed when the analysis was performed by briefly trained high-school students: r = 0.980, y = 0.949x + 23 mg/L. Performance decreased when both collection and analysis were performed by laymen: r = 0.880, y = 0.870x + 186 mg/L.

Intracellular magnesium content of mononuclear blood cells and granulocytes isolated from leukemic, infected, and granulocyte colony-stimulating factor-treated patients.

The intracellular magnesium (Mg) concentration of granulocytes and mononuclear blood cells (MBCs) was determined in cells isolated from patients with several disorders. The mean (+/-SD) Mg content of MBCs isolated from patients diagnosed with lymphocytic leukemia, myelocytic leukemia, or infection; from patients treated with granulocyte colony-stimulating factor (G-CSF); and from healthy volunteers (control group) was 2.3 (+/-0.6), 3.3 (+/-0.5), 4.1 (+/-0.8), 3.9 (+/-0.4), and 3.9 (+/-0.6) fmol/cell, respectively. The Mg content of MBCs isolated from patients with lymphocytic and myelocytic leukemia, but not those from patients with infection or receiving G-CSF treatment, were significantly lower (P < 0.001) than those from the control subjects. The mean Mg concentration of granulocytes obtained from lymphocytic leukemia, myelocytic leukemia, infection, and G-CSF patients and from the control group was 3.2 (+/-0.9), 3.4 (+/-0.5), 3.8 (+/-0.6), 4.5 (+/-0.6), and 4.6 (+/-0.6) fmol/cell, respectively. Granulocytes isolated from leukemic and infectious patients yielded lower intracellular Mg concentrations (P < 0.005) than those from patients receiving G-CSF and the control group. This study demonstrates that intracellular Mg content is altered in several pathological states. Several factors, including depleted Mg stores or altered intracellular Mg binding sites, could be responsible for these changes. Apparently, intracellular Mg content may be of use in assessing total body Mg status.

Cardiac troponin T levels in umbilical cord blood.

OBJECTIVE: We sought to determine cardiac troponin T concentrations in umbilical cord plasma from normal and complicated pregnancies. STUDY DESIGN: At the time of delivery, umbilical cord arterial and venous samples were collected from 209 neonates, and cardiac troponin T levels were measured by immunoassay. Comparisons of clinical factors were made between neonates with normal and elevated cardiac troponin T levels. Significance was deemed present at P <.05. RESULTS: Twelve neonates had elevated cardiac troponin T levels. Exposure to magnesium sulfate was associated with an elevated cardiac troponin T level (relative risk, 33.2; 95% confidence interval, 7.7-143). CONCLUSIONS: Cardiac troponin T levels were elevated in neonates exposed to magnesium sulfate in utero. The explanation of this finding and its clinical significance are unknown. Characterization of fetal and neonatal troponin T requires further study.