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PubMed1998

Considerations in reference values for nerve conduction studies.

Despite the universal application of reference values, understanding their production and underlying limitations is often overlooked. Without a deeper consideration for this issue, opportunities for treatment may be missed or misdiagnosis may occur. This article reviews relevant biostatistical issues in the generation of reference intervals and subsequent errors that may occur. Further discussion includes recommendations on how to correct statistical errors, as well as more recent methods for distinguishing between "healthy" and "diseased."

Biometry↗

PubMed2005

Reference values for nocturnal home polysomnography in primary schoolchildren.

Abbreviated home polysomnography may be an alternative to laboratory polysomnography in children but is not yet generally accepted, partly due to a lack of reference values. Also, there are no normative data on respiratory events obtained using nasal prongs. We determined the prevalence and frequency of central, obstructive, and mixed apneas and hypopneas in a population-based sample of 50 children (mean age 10.1 years) using abbreviated home polysomnography and nasal prongs. We also determined the frequency of movements/arousals and body position changes. All children had central apneas. Obstructive apneas, mixed apneas, and hypopneas were found in 36%, 6%, and 14% of children, respectively. Average number of central, obstructive, and mixed apneas; hypopneas; movement/arousals; and body position changes per hour of sleep was 1.5, 0.1, 0.01, 0.02, 8.2, and 3.7, respectively. The corresponding cutoff values (mean plus 2 standard deviations or 95th centile) were 3.7, 0.7, 0.1, 0.2, 13.4, and 9.1, respectively. We did not find significant gender differences regarding any sleep variable under study. The presented reference values may help clinicians and researchers to improve the interpretation of abbreviated home polysomnography in school-age children.

Child↗

PubMed2003

Establishment of age-dependent reference values for IgA subclasses.

BACKGROUND: Recently, subclass-specific antisera have been introduced for application in a nephelometric assay. The aim of this study was to establish age-dependent reference values for serum concentrations of the two IgA subclasses in children and adults. METHODS: Serum levels of IgA1 and IgA2 were measured by automated immunonephelometry in samples from 235 clinically healthy children between 6 months and 18 years of age and 36 healthy adults. RESULTS: Both IgA1 and IgA2 were detectable in all samples, and both IgA1 and IgA2 increased with increasing age. In adults, the mean value for IgA1 is 1.46 g/l for IgA2 0.21 g/l and for total IgA 1.94 g/l. Individual IgA2 values correlate significantly (p < 0.0001) with IgA1 values (r(2) = 0.5433). In addition, there was a highly significant (p < 0.0001) correlation (r(2) = 0.9530) between the measured total IgA and the sum of the two IgA subclasses indicating that immunonephelometry using highly specific polyclonal antisera might be superior to other methods. CONCLUSIONS: These results and the availability of age-dependent reference values make it worthwhile to reassess the role of IgA subclasses in immunodeficiency and autoimmune diseases where conventional methods have led to conflicting results.

Adult↗

PubMed2000

Partitioning of dead space--a method and reference values in the awake human.

Although dead space is often increased in disease, it is not frequently measured in the clinic. This may reflect that an adequate method as well as reference values are missing. Healthy males and females, n=38, age 20-61 yrs, were connected to a pneumotachograph and a fast CO2 analyser after radial artery catheterization. The physiological dead space was partitioned into airway and alveolar dead space using a delineation principle denoted the pre-interface expirate. Physiological dead space was 201+/-41 mL in males and 150+/-34 mL in females. Dead space values were depending upon parameters reflecting lung size (predicted total lung capacity), breathing pattern and age. After multiple correlation the variation decreased and differences between males and females disappeared. The residual SD was then for physiological dead space 18.9 mL. The clinical use of the new method for determination of dead space can be based upon reference values, with a more narrow range than previous data.

Adult↗

PubMedDate not supplied

Reference values for selected ophthalmic diagnostic tests of the ferret (Mustela putorius furo).

PURPOSE: To perform selected ophthalmic diagnostic tests in healthy ferrets with the aim of establishing normal physiological reference values for this species. METHOD: A total of 15 healthy, unrelated ferrets were used to test most of the parameters in this investigation. Eight of the 15 ferrets were used for central corneal thickness evaluation. Ages varied from 1.5 to 6 years of age. Selected diagnostic ocular tests were performed including Schirmer tear test, tonometry using an applanation tonometer (Tonopen), central corneal thickness using an ultrasonic pachymeter (Sonomed, Micropach, Model 200P +) and culture of the normal conjunctival bacterial flora. RESULTS AND DISCUSSION: Staphylococcus sp. and Corynebacterium sp. were isolated from healthy conjunctival and eyelid margins, suggesting they are normal constituents of the conjunctival flora of the ferret. Results for selected ocular diagnostic tests investigated here for the ferret eye were as follows: intraocular pressure: 14.50 +/- 3.27 mmHg; Schirmer tear test: 5.31 +/- 1.32 mm/min; central corneal thickness: 0.337 +/- 0.020 mm. No statistically significant differences between ages or genders were found for any of the results. The reference data for the ocular tests obtained in this investigation will help veterinary ophthalmologists to more accurately diagnose ocular diseases in the ferret. Knowledge of these reference values will be particularly useful to diagnose discrete or unusual pathological changes of the ferret eye.

Animals↗

PubMed1992

Reference values for immunoglobulin kappa and lambda light chains and the kappa/lambda ratio in children's serum.

We analyzed 708 serum samples from healthy children and adolescents by immunonephelometry to obtain reference values for the immunoglobulin kappa (kappa) and lambda (lambda) light chains and for their ratio at a time of life when immunoglobulin synthesis is maturing and continually being stimulated. The lambda chain concentration that is to be maintained throughout the child's life is reached very early, just after 1 year, whereas the concentration of the kappa chains, which increases gradually, reflects the concentration of the immunoglobulins as a whole. These reference values may be useful for studying kappa and lambda chains in illnesses involving the immune system in children.

Adolescent↗

PubMed1998

Clinical chemistry variables in normal elderly and healthy ambulatory populations: comparison with reference values.

Laboratory values of the most commonly assayed clinical chemistry variables were determined in selected elderly and healthy ambulatory populations. The upper and lower limits (2.5 and 97.5 fractiles) were compared with the adult reference values in use in university hospitals of Switzerland. The results suggest that conventional adult reference values can be used for most variables in the elderly and that these values are also useful in an ambulatory population.

Aged↗

PubMed2004

Reference values of fetal ductus venosus, inferior vena cava and hepatic vein blood flow velocities and waveform indices during the second and third trimester of pregnancy.

OBJECTIVE: Our objective was to establish reference values for ductus venosus, inferior vena cava and hepatic vein flow velocities during ventricular systole (S-wave) and diastole (D-wave), the lowest forward velocity during atrial contraction (a-wave), the intensity-weighted mean flow velocity (Vmean) and different calculated indices. METHODS: Venous flow velocity waveforms were obtained from 329 singleton pregnancies at 20-42 weeks of gestation by pulsed-wave color Doppler. Reference values were constructed by means of a quadratic regression model after logarithmic transformation of original data. RESULTS: With advancing gestational age the peak velocity index for the vein (PVIV) and pulsatility index for the vein (PIV) decreased whereas blood flow velocities increased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein. Values for PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. During atrial contraction there was a blood flow towards the fetal heart in the ductus venosus, whereas in the inferior vena cava and in the hepatic vein blood flow was either in the opposite from the fetal heart (reverse flow), or there was absent flow (zero flow) or flow was towards the fetal heart (positive flow). CONCLUSIONS: The reference ranges and calculated velocities established in this study may be utilized in studies dealing with the role of ductus venosus and inferior vena cava blood flow in fetuses with chromosomal abnormalities or congenital heart disease as well as hypoxic conditions. We speculate, that the reduction in PVIV and PIV with advancing gestational age may reflect a decrease in cardiac afterload as a result of maturation of diastolic ventricular function.

Blood Flow Velocity↗

PubMed1979

The neonatal blood count in health and disease. I. Reference values for neutrophilic cells.

Reference ranges for absolute total neutrophils/mm3, absolute immature neutrophils/mm3, and the fraction of immature to total neutrophils (I:T proportion) during the first 28 days of life are developed from 585 peripheral blood counts obtained from 304 normal neonates and 320 counts obtained from 130 neonates with perinatal complications demonstrated to have no statistically significant effect on neutrophil dynamics. Perinatal factors other than bacterial disease which significantly alter neutrophil dynamics include maternal hypertension, maternal fever prior to delivery, hemolytic disease, and periventricular hemorrhage. The predictive value of these reference ranges in identifying bacterial disease in the first week of age varies with the neutrophil factor evaluated and the clinical setting. Neutropenia in the presence of respiratory distress in the first 72 hours had an 84% likelihood of signifying bacterial disease, whereas neutropenia in the presence of asphyxia had a 68% likelihood of signifying bacterial disease. An abnormal I:T proportion had an accuracy of 82% and 61%, respectively, in the same clinical settings. Elevations of either immature or total neutrophils were less specific. Interpretation of abnormal neutrophil factors must include consideration of both infectious and noninfectious perinatal events.

Erythrocyte Count↗

PubMed1995

Reference values obtained by kernel-based estimation of quantile regressions.

In this paper, we study the problem of estimating non-parametrically a quantile regression curve as it applies to computing reference values. We propose an automatic procedure that uses a symmetrized nearest-neighbor kernel estimator of conditional distributions. We also discuss ways of measuring the dispersion of quantile regression estimator. One is based on the asymptotic distribution of such quantiles, while the other relies on the bootstrap method. The results of a small simulation study show that the methods of the paper perform rather well even in a situation where a good parametric solution is available. As an example, we analyze a small part of a data set that was collected to establish reference values for blood velocity in different parts of the umbilical cord of human fetuse as they grow toward birth.

Biometry↗

PubMed1992

Determination of blood constituents reference values in broilers.

Eight hundred broilers were examined to define the reference values of nine blood constituents (total proteins, albumin, total and free cholesterol, triglycerides, aspartate aminotransferase (AST), alkaline phosphatase (ALP), calcium, and phosphorus). The broilers, coming from 20 different commercial poultry operations, were equally divided into different groups according to age (21 and 45 days), strain (Arbor Acres and Hybro), sex, and sampling season (summer or winter). Age and sampling season were the variation sources that most influenced the values of the hematochemical variables examined. The interaction of age with strain influenced total proteins total and free cholesterol, triglycerides, and ALP. The interaction of age with sampling season influenced all hematochemical constituents except triglycerides. Reference limits defined by .975 and .025 fractiles were computed for each blood constituent according to the significance of different variation sources and their combinations. Reference limits defined herein could be used as indicators of metabolic and health conditions of a poultry farm.

Age Factors↗

PubMed1994

Reference values for apolipoprotein A-I and apolipoprotein B in serum still depend on choice of assay techniques.

In a study with young children receiving growth hormone treatment, it was necessary to re-establish reference values for various blood components, e.g. apolipoproteins A-I and B. We find that considerable method-to-method variation still exists. We used the DuPont Dimension analyzer (D) and the Beckman Array analyzer (B) systems and a third procedure with Orion reagents and a Kone Analyzer (K). We investigated if assay results may be pooled or exchanged within our study. In 59 serum samples we measured apolipoprotein A-I and apolipoprotein B (n = 58) and calculated the orthogonal regression equations y = a(Sa) x + b(Sb). For apolipoprotein A-I the results are: (I) B = 1.165 (0.065) D - 0.193 (0.077), Syx = 0.055; with r = 0.922 and (II) K = 0.831 (0.056) D - 0.190 (0.066), Syx = 0.055; with r = 0.898. For apolipoprotein B the equations are: (III) B = 1.586 (0.137) D - 0.246 (0.100), Syx = 0.061; with r = 0.840 and (IV) K = 0.869 (0.065) D + 0.251 (0.048), Syx = 0.044; with r = 0.875. According to Passing & Bablok, the slopes and intercept values are 1.093 and -0.126; 0.848 and 0.167; 1.500 and -0.185; 0.880 and 0.249. The overall impression is the same for both regression methods: comparability had not yet been achieved by early 1993, particularly not for apolipoprotein B, and reference values differ significantly depending on the selected methodology.

Apolipoprotein A-I↗

PubMed1986

Autonomic nerve function tests. Reference values in healthy subjects.

Autonomic nerve function was evaluated by deep breathing (E/I heart rate ratio) and tilt table tests (acceleration index, brake index, and blood pressures) in 56 healthy subjects in order to find reference values. The results showed that the E/I ratio, the acceleration index and the brake index fell with increasing age. There was no influence of age on the systolic and the diastolic blood pressure reactions to tilt. Age-related reference values are needed in the evaluation of autonomic neuropathy indices.

Adolescent↗

PubMed2000

[Anthropometry and the reference values of body composition by bioelectrical impedance in the adult population of L'Hospitalet de Llobregat].

BACKGROUND: The aim of the present study was to assess the anthropometric variables and the reference values of body composition in the adult population of L'Hospitalet de Llobregat, due to the lack of epidemiological studies on this matter in Spain. PATIENTS AND METHODS: We studied 234 normal subjects, 134 males, mean age 41.4 years, and 134 females, mean age 40.7 years, selected from the census of L'Hospitalet de Llobregat and representative of its population in sex and age. We determined anthropometric characteristics, body weight, height, body mass index, waist-hip ratio and body composition parameters: total body water, free fat mass, fat mass and body fat by bioelectrical impedance analyzer. RESULTS: Twenty-four males and 33 females were obese, and out of them 2 males and 4 women presented morbid obesity. The body mass index was higher either in males (p = 0.017) or in females (p = 0. 0001) in the last decades in relation to first decade, and in women was as consequence of higher fat mass (p = 0.0001). The waist-hip ratio was 0.93 (0.08) in male and 0.79 (0.07) in female, and it was high in males in the last decades. CONCLUSION: The present study points out the high prevalence of obesity in our city and the anthropometric characteristics and reference values of body composition in the normal population of L'Hospitalet de Llobregat, remarking the high body mass index in the last decades, especially in women due to an increase of fat mass. The waist-hip ratio was high in males in the last decades.

Adolescent↗

PubMed1998

[Reference values of urinary orotic acid in a healthy Tunisian population].

BACKGROUND: Orotic acid (OA) is an intermediary metabolite of pyrimidine synthesis. An elevation of urinary orotic acid excretion has been described in congenital defect of the urea cycle enzymes and in primary orotic aciduria. Several techniques have been used to measure OA and many reference values are published without considering age and sex. POPULATION AND METHODS: The reference values of urinary OA excretion, expressed in mumol/mmol of creatinine, are reported in a healthy Tunisan population using a colorimetric method. The study included 20 men and 20 women (age = 31 +/- 11 years) and 30 children aged from 3 days to 8 years. RESULTS: There was a significant increase (P < 0.01) of urinary OA excretion in women (4.38 +/- 1.35) compared to men (3.26 +/- 0.80) and of children (5.03 +/- 1.14) compared to adults (3.82 +/- 1.24). Urinary OA excretion was significantly higher among children aged less than 1 year compared to older children. CONCLUSION: It is necessary for every laboratory practicing this kind of exploration to have its own norms which depend on both age and sex.

Adult↗

PubMed1988

Reference values for fructosamine concentrations in children's sera: influence of protein concentration, age, and sex.

Fructosamine and protein (total and fractionated) were measured in the serum of 170 normal children, ages two weeks to 15 years. The mean fructosamine concentration was 2.12 mmol/L, 5% lower than the mean value observed for adults. We observed no sex-related difference in fructosamine values, but saw a pronounced age dependency of reference values. For children younger than three years, the mean concentration of fructosamine was 15% lower than in adults, but glycated protein concentrations increased with age, reaching essentially adult values by age six years. Expressing fructosamine concentrations per gram of serum total protein or of albumin weakened the influence of age, but did not eliminate it completely. We report reference intervals for fructosamine concentrations in children's sera.

Adolescent↗

PubMed1992

Reference values for renal concentrating capacity in children by the desmopressin test.

Reference values are reported for maximal renal concentrating capacity in children using intranasally administered desmopressin. The report is based on 591 tests in 473 healthy children aged 0.5-13 years. The concentrating capacity increased markedly during the first years of life and reached a plateau at the age of 3 years. The mean value minus two standard deviations was 525 mosmol/kg at 1 year of age and 825 mosmol/kg at 3 years of age.

Administration, Intranasal↗

PubMed1996

Comparison of spirometric reference values for Caucasian and African American blue-collar workers.

Interpretation of lung-function test results, specifically the forced vital capacity and forced expiratory volume in one second, generally involves the comparison of these parameters with reference values based on an individual's age, height, sex, and race. Such comparisons are often used to make important decisions concerning an individual, such as job placement or disability rating. Several studies have shown that predicted values for African Americans are approximately 15% less than those for Caucasians, most likely because of the use of standing height to estimate the size of the thorax. When an adjustment for race is applied to reference values based on a Caucasian population, a single value (15%) is usually applied to all individuals. When using a group of blue-collar workers (766 Caucasian and 633 African-American subjects) without any race adjustment, 10.2% of the Caucasians and 37.4% of the African-American subjects were below the lower limit of normal. When a single adjustment factor was used, 11.5% of the African-American subjects were below the lower limit of normal. Between-subject variability within an ethnic group was far greater than variability between groups. Our results suggest that although a difference between Caucasian and African-American test results for forced vital capacity and forced expiratory volume in one second exists, an application of a single adjustment factor universally applied to all individuals, regardless of their age, sex, and height, is not optimal, and alternative approaches are needed.

Adolescent↗