Para-aminobenzoic acid (PABA) used as a marker for completeness of 24 hour urine: effects of age and dosage scheduling

OBJECTIVE: To examine the age dependency of the urinary para-aminobenzoic acid (PABA) excretion, and if a delayed PABA excretion can be overcome by advancing intake schedule; and to examine the recovery of PABA in fractionated urinary samples collected during 24 h after single and repeated doses of PABA. DESIGN: Cross-over study with subjects randomized to start with recommended schedule of PABA administration (80 mg at 08:00, 12:00 and 18:00; PABA18) and then an advanced schedule (80 mg at 08:00, 12:00 and 15:00; PABA15) or vice versa. One subgroup of eight subjects collected individual urine specimens for 24 h after a morning dose of 80 mg of PABA, and another subgroup of 10 subjects collected individual urine specimens for 24 h after ingestion of 80 mg of PABA three times at mealtimes. SUBJECTS: Employees and relatives from the Danish Food Administration. SETTING: Ninety-nine healthy volunteers (61 females and 38 males) aged 30-91 y. RESULTS: Linear regressions for PABA15 and PABA18 demonstrate significantly less recovery with age (PABA15: r(2)=0.1784, P=0.0002; PABA18: r(2)=0.1273, P=0.0019). Linear regression of DeltaPABA (PABA15-PABA18) with age showed the best fit line to be horizontal (slope -0.0066, P=0.89; 95% CI -0.1046, 0.0915) and with a Y-intercept not significantly different from 0 (1.575; 95% CI -4.176, 7.326). In this population the lower limit for complete 24 h urine collection was 79.2%. After a single dosage of 80 mg PABA 70-85% was recovered after 8 h. Within 16 h after ingestion of 240 mg PABA at recommended hours the lowest acceptable recovery (78.1%) was reached. CONCLUSION: There is a gradual decline of PABA recovery with age that cannot be overcome by advancing the dosage schedule. Because of a lower delimiting PABA recovery for the elderly, some 24 h collections in this age group will be rejected unjustly (false-negatives). Also, with the currently recommended dosage schedule (PABA taken with the main meals) the risk of false-positive 24 h urine collections prevails. With refinement of the PABA test procedure, ie employing a specific analytical method and age-dependent cut-off values, the test may achieve a higher specificity and sensitivity.     

para-amino benzoic acid in the assessment of completeness of 24-hour urine collections from hospital outpatients and the effect of impaired renal function.

Eighteen (29%) of 24-h urine collections made by 63 hospital outpatients attending a gastroenterology clinic were incomplete, as judged by 24 h urine recovery of an oral marker, para-amino benzoic acid (PABA), despite more than the usual efforts to obtain complete collections. Incomplete collections contained significantly less sodium, urea and total nitrogen than full collections. Average outputs were 134 mmol and 103 mmol per day for sodium (P less than 0.02); 301 mmol and 223 mmol for urea (P less than 0.001); and 10.1 g and 8.3 g nitrogen (P less than 0.01) in the complete and incomplete collections respectively. In renal outpatients with a plasma creatinine in excess of 125 mumol per litre, urine recoveries of PABA were reduced, but within the expected range in renal patients whose plasma creatinine was normal.     

Use of low-glycaemic index bread to reduce 24-h blood glucose: implications for dietary advice to non-diabetic and diabetic subjects

The present study investigated the effect of a simple dietary change on 24-h blood glucose. In a randomized cross-over design, 10 healthy subjects were prescribed a low-glycaemic-index (LGI) diet and a high-glycaemic-index (HGI) diet. The diets were identical with the exception of the type of bread consumed (LGI or HGI). Glucose concentrations over 24 h were measured using a continuous glucose monitoring system. The LGI diet resulted in a lower mean glucose response compared with the HGI diet over 24 h (P=0.135), during the day (P=0.171) and at night (P=0.100). Similarly, the 24-h, daytime and overnight incremental area under the curve for glucose following the LGI diet was consistently lower than following the HGI diet (P=0.093, P=0.132 and P=0.061, respectively). The results demonstrate how a very simple dietary change can favourably alter overall blood glucose concentrations. Such small modifications to the diet, if adopted in the long term, could improve glucose control and consequently reduce the risk of chronic disease in both diabetic and non-diabetic individuals.     

Use of low-glycaemic index bread to reduce 24-h blood glucose: implications for dietary advice to non-diabetic and diabetic subjects

The present study investigated the effect of a simple dietary change on 24-h blood glucose. In a randomized cross-over design, 10 healthy subjects were prescribed a low-glycaemic-index (LGI) diet and a high-glycaemic-index (HGI) diet. The diets were identical with the exception of the type of bread consumed (LGI or HGI). Glucose concentrations over 24 h were measured using a continuous glucose monitoring system. The LGI diet resulted in a lower mean glucose response compared with the HGI diet over 24 h (P=0.135), during the day (P=0.171) and at night (P=0.100). Similarly, the 24-h, daytime and overnight incremental area under the curve for glucose following the LGI diet was consistently lower than following the HGI diet (P=0.093, P=0.132 and P=0.061, respectively). The results demonstrate how a very simple dietary change can favourably alter overall blood glucose concentrations. Such small modifications to the diet, if adopted in the long term, could improve glucose control and consequently reduce the risk of chronic disease in both diabetic and non-diabetic individuals.     

Sensitivity and specificity of published strategies using urinary creatinine to identify incomplete 24-h urine collection

OBJECTIVE: Although urinary creatinine has been used to identify incomplete 24-h urine in numerous epidemiologic studies, information on its utility is limited. We examined the sensitivity and specificity of several strategies that use creatinine to identify incomplete urine using the p-aminobenzoic acid (PABA) check method as reference. METHODS: Subjects were 654 female Japanese dietetic students 18-22 y of age. A single 24-h urine sample was collected, with recording of the time of the start and end of the collection period and missing urine volume. Simultaneous administration of PABA was done to assess completeness. The sensitivity and specificity of five strategies derived from the literature that used creatinine to identify incomplete urine were calculated as the proportion of incomplete and complete urine correctly identified, respectively. RESULTS: A total of 7.6% of subjects was identified as having incomplete urine by PABA (PABA recovery <85%). This proportion significantly (P < 0.0001) decreased (to 5.5%) after considering self-reported collection time and missing urine volume in the calculation of total urine volume. The sensitivity and specificity of the strategy of Knuimann et al. (incomplete urine = <0.7 of [mmol urinary creatinine x 113]/[21 x kilograms of body weight]) were 0.47 and 0.99, respectively. The corresponding values of other strategies were 0.11-0.22 and 0.57-1.00, respectively. CONCLUSION: At least in well-motivated populations in which the proportion of incomplete urine is presumed to be small, the strategy of Knuimann et al. and consideration of the self-reported collection time and missing urine volume in the estimation of total volume may be useful.     

The estimation of 24-hour urine urea nitrogen excretion from urine collections of shorter duration in continuously alimented patients

Urine urea nitrogen excreted in 24 hr is used to estimate nitrogen balance in patients. Normal diurnal variation of urea excretion may be less pronounced in patients alimented continuously, and a urine collection of shorter duration may be representative of the 24-hr excretion. Five stabilized trauma center patients on continuous enteral or parenteral alimentation were studied with six consecutive 4-hr urine collections analyzed for urine urea nitrogen content. Excretion rates for various lengths of urine collection were compared with the 24-hr excretion rate. Urine collections spanning 4 or 8 hr frequently exceeded an error of 10% in predicting 24-hr urea nitrogen excretion, while collections of 12 hr or more had small errors. A comparison of three consecutive 8-hr collections was suggestive of diurnal variation existing under these conditions.     

Weekend versus weekday urine collections in assessment of stone-formers.

Twenty-four-hour urine collections are an important part of the metabolic evaluation of stone-formers, but are difficult for patients at work. At weekends the results might be different. Forty-five stone-formers who worked at day jobs from Monday to Friday collected urine for 24 h on a normal working day and also on a Saturday or Sunday and the differences were evaluated. Average 24 h urine volume was higher on weekdays than at weekends. Calcium, oxalate, and uric acid excretion did not differ. These results imply an increased risk of crystalluria at the weekend. Therefore weekend collections are most likely to show abnormalities and should be acceptable to clinicians.     

Albuminuria assessed from first-morning-void urine samples versus 24-hour urine collections as a predictor of cardiovascular morbidity and mortality

Screening for albuminuria has been advocated because it is associated with cardiovascular morbidity and all-cause mortality. The "gold standard" to assess albuminuria is 24-hour urinary albumin excretion (UAE). Because 24-hour urine collection is cumbersome, guidelines suggest measuring albuminuria in a first morning void, either as urinary albumin concentration (UAC) or adjusted for creatinine concentration, the albumin:creatinine ratio (ACR). To decide which albuminuria measure to use in clinical practice, it is essential to know which best predicts clinical outcome. In a sample representative of the Groningen (the Netherlands) population (n = 3,414), the authors compared UAC, ACR, and UAE as predictors of cardiovascular events and all-cause mortality. During a median follow-up of 7.5 years, which ended December 31, 2005, they observed 278 events (a major adverse cardiovascular event or mortality). The area under the receiver operating characteristic curve predicting events was 0.65 for UAE, 0.62 for UAC (P = 0.06 vs. UAE), and 0.66 for ACR (P = 0.80 vs. UAE; P = 0.01 vs. UAC). When sex-specific subgroups were considered, UAE was superior to UAC in predicting outcome (P = 0.04) for females, whereas, for males as well as females, no difference was found between ACR and UAE. To predict cardiovascular morbidity and all-cause mortality, measuring ACR in a first-morning-void urine sample is a good alternative to measuring 24-hour UAE.     

Ingested fat oxidation contributes 8% of 24-h total energy expenditure in moderately obese subjects

The role of ingested fat in the etiology of obesity is controversial. The aims of this study were to determine the contributions of ingested fat oxidation to: 1) 24-h total energy expenditure (TEE), and 2) substrate oxidation during acute stationary cycle exercises in adult humans. Healthy, moderately obese (n = 18; BMI = 31 +/- 1 kg/m2) subjects (8 men; 10 women) were each studied in a whole-room calorimeter for 24 h. They were fed mixed meals (55, 30, and 15% as energy from carbohydrate, fat and protein, respectively) to maintain energy balance. Each subject performed 1255-kJ cycle exercises at 50% VO2max in the calorimeter. Study test meal fat was labeled with carbon-13 (13C). Ingested fat oxidation was estimated from breath 13CO2 excretion and the subject's chamber CO2 production. Total fat and carbohydrate oxidations were estimated from nonprotein respiratory quotient (NP-RQ) values. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidations. TEE was estimated from gas exchanges; 28 +/- 3% of ingested fat was oxidized and it provided 8 +/- 1% of 24-h TEE. During cycle exercises, ingested fat provided 50% of total fat oxidized and 13.0 +/- 2% of energy expended. Endogenous fat oxidation contributed 10.4 +/- 3% of energy expenditure during cycle exercises. This study extended to 24-h observations of previous studies that lasted 6-9 h on ingested fat oxidation in humans. Understanding the factors that promote ingested fat oxidation could lead to more effective obesity intervention programs.     

Validity of the 24-hr. recall. Analysis of data obtained from elderly subjects.

Tests of the validity of the 24-hr. dietary recall were done by comparing actual with recalled intakes for eight nutrients and the MAR (mean adequacy ratio) for a sample of seventy-six subjects age sixty years or older. Validity was tested by using paired-t tests and regression analysis. In the paired-t test, no significant difference was found between the mean recalled and the mean actual intake of nutrients, with the exception of calories. Using regression analysis, results indicated that for three of the eight nutrients considered (calories, protein, and vitamin A), small intakes tend to be over-reported and large intakes under-reported (p less than .05). Thus, for these three nutrients, the recall seems to be statistically conservative for group comparisons; it would seldom, if ever, indicate a difference in intake where no difference exists. But, it could yield a false negative, i.e., an indication of no significant difference, when, in fact, a difference does exist. Clearly, more research is needed, both to replicate this study and to develop techniques with greater internal validity for comparing the dietary intakes of groups.     

Development of tolerance to endogenous opiates activated by 24-h food deprivation.

Four experiments assessed the effects of exposure to 24-h food deprivation on the tail-flick latency of rats exposed to a temperature stimulus. Confirming previous studies, Experiment 1 showed that food deprivation gave rise to analgesia, as indicated by increased tail-flick latencies, that was antagonized by naloxone. Experiment 2 found that analgesia was greatly reduced after five exposures to periods of 24-h food deprivation (alternating with 24-h free access to food), indicating the development of tolerance. Experiments 3 and 3a examined the development of tolerance to the analgesic effects of morphine following repeated morphine injections, saline injections, and exposure to 24-h food deprivation plus saline injections. The combined results of both experiments provided evidence that repeated exposures to either morphine or food deprivation, produced greater tolerance to morphine than did exposures to saline. That food deprivation was cross-tolerant with morphine indicated that tolerance to food deprivation-induced analgesia involved opioid mechanisms. The relevance of opioid tolerance to psychobiological models of feeding and to the development of an animal model of anorexia nervosa was discussed.     

1-Hydroxypyrene concentrations in first morning voids and 24-h composite urine: intra- and inter-individual comparisons

Urinary 1-hydroxypyrene (1-OHP) has been suggested as an exposure biomarker for polycyclic aromatic hydrocarbons (PAHs). However, it remains unknown whether a first morning urine sample can be used to reflect average exposure. In this paper, we examine intra-individual differences and inter-individual associations between first morning voids and 24-h composite urine samples. The analysis was performed using data collected from 100 adults who had a wide range of PAH exposure due to differences in their occupation, e.g., coke oven workers vs. non-coke oven workers. For each subject, all the urine voids within each of two 24-h measurement periods were collected. Results showed a significant (40% to 62%) intra-individual difference between first morning voids and 24-h urinary 1-OHP concentrations (in ng/ml urine). Creatinine adjustments of 1-OHP concentrations (in micromol/mol urinary creatinine) reduced the intra-individual difference by approximately 10%. Across all the subjects, a high overall correlation (r=0.76) was observed between first morning and 24-h average 1-OHP concentrations. Work environment and sampling season were found to significantly affect the relationship between first morning and 24-h 1-OHP concentrations. An increase of 1 ng/ml of first morning urinary 1-OHP predicted an increase of 0.5 and 0.25 ng/ml of 24-h urinary 1-OHP for coke oven workers and non-coke oven workers, respectively. Data collected in a winter season showed a higher correlation between first morning and 24-h concentrations than data collected in a fall season. Creatinine adjustments did not significantly improve overall correlations between first morning void and 24-h measurements, but increased total variances for 24-h urines explained by first morning urines in coke workers.     

Food frequency questionnaires and overnight urines are valid indicators of daidzein and genistein intake in U.S. women relative to multiple 24-h urine samples

Data regarding convenient, valid methods for measuring U.S. isoflavone intake are limited. We evaluated a soy food questionnaire (SFQ), the Willett food frequency questionnaire (FFQ), and overnight urine samples relative to excretion in 24-h urine samples. We also described intake among women in a high-risk program for breast or ovarian cancer. Between April 2002 and June 2003, 451 women aged 30 to 50 yr with a family history of breast or ovarian cancer completed the SFQ and FFQ. Of them, 27 provided four 24-h and overnight urine specimens. In these women, 24-h sample measures were correlated with SFQ estimates of daidzein (Spearman r = .48) and genistein (r = .54) intake, moderately correlated with the Willett FFQ (daidzein r = .38, genistein r = .33), and strongly correlated with overnight urine excretion (daidzein r = .84, genistein r = 0.93). Among all 451 SFQ respondents, mean (median) daidzein and genistein intakes were 2.8 (0.24) and 3.9 (0.30) mg/day. Primary sources of both were soymilk, soy nuts, and tofu. We conclude that targeted soy food questionnaires, comprehensive FFQs, and multiple overnight urines are all reasonable options for assessing isoflavone intake in epidemiologic studies.     

Effects of Para-Aminobenzoic Acid (PABA) Form and Administration Mode on PABA Recovery in 24-Hour Urine Collections

Para-aminobenzoic acid (PABA) has long been used as an objective measure to assess completeness of 24-hour urine collections. However, pharmaceutical-grade PABA for human ingestion is not available in the United States. An alternative, the potassium salt of PABA, aminobenzoate potassium, can be obtained for clinical use, although it has not yet been validated in this role. Both PABA and aminobenzoate potassium can be directly ingested in their tablet or capsule forms or added to food before consumption. Our aim was to investigate the effect of form (PABA vs aminobenzoate potassium) and administration mode (directly ingested as a tablet/capsule vs added to food) on urinary PABA recovery levels. Twenty healthy participants underwent 3 test days separated by two 24-hour wash-out periods. Three test conditions, one on each test day, were investigated in randomized order: PABA tablet, aminobenzoate potassium capsule, and PABA or aminobenzoate potassium in food. Ingestion of each dose was supervised and participants performed the 24-hour urine collections while free-living. The 24-hour urine collections were analyzed for PABA recovery (%R) levels using a colorimetric assay. Recoveries 85% to 110% were deemed complete and those >110% were reanalyzed by high pressure liquid chromatography and mass spectrometry. Only complete collections (>85%R) were included in analyses. The recovery for the PABA tablet, aminobenzoate potassium capsule, and PABA/aminobenzoate potassium in food were similar at 98.8%R±2.0%R, 95.1%R±2.3%R, and 93.2%R±2.1%R, respectively, and did not differ significantly. These results suggest that aminobenzoate potassium may be used as an alternative to PABA for assessing the completeness of 24-hour urine collections and to track compliance with consuming provided diets in community-dwelling studies.     

Muscularity and adiposity in addition to net acid excretion as predictors of 24-h urinary pH in young adults and elderly

OBJECTIVE: In patients with nephrolithiasis, an inverse relationship between 24-h urinary pH (24h-UpH) and body weight has been reported. Whether body composition indices and 24h-UpH are similarly associated in healthy subjects needs investigation. DESIGN: Cross-sectional, retrospective analysis. SETTING: Dortmund, Germany and Gothenburg, Sweden. SUBJECTS: Healthy young adults (18-23 years; n=117) and elderly (55-75 years; n=85) having a mean body mass index (BMI) of 22.80+/-3.4 and 25.3+/-3.9 kg/m2, respectively. METHODS: Anthropometric data, 24h-UpH, and 24-h urinary excretion rates of net acid (NAE), creatinine, and urea were determined. After adjusting for urea (reflecting protein intake), renal creatinine output was used as a biochemical marker for muscularity. The BMI served as a marker of adiposity. RESULTS: NAE, body weight, and BMI were significantly (P<0.05) higher, and height and creatinine significantly lower in the elderly, whereas body-surface area (BSA) was not different. Step-wise multiple regression analysis using BSA-corrected urinary variables revealed NAE as the primary predictor of 24h-UpH (with R2 values of 0.64 and 0.68 in young adults and elderly, respectively, P<0.0001), followed by urea (P<0.0001), creatinine (P<0.05), and BMI (P<0.05 for the young adults and P=0.12 for the elderly). These associations were negative for NAE and BMI, and positive for urea and creatinine. CONCLUSIONS: Muscularity (i.e. creatinine adjusted for urea) and particularly in the group of young adults, adiposity (i.e. BMI) proved to be modest, but significant predictors of 24h-UpH. Future research should focus on more obese subjects in whom insulin resistance and particular kidney functions should also be examined to further substantiate the role of obesity in low-urine pH-associated conditions, for example, nephrolithiasis.     

Sampling of urinary cadmium: differences between 24-h urine and overnight spot urine sampling,and impact of adjustment for dilution

Purpose  

Urinary cadmium (U-Cd) sampling can be done either by 24-h urine or spot urine sampling, and adjustment for dilution is usually needed. The choice of sampling period and adjustment technique could, however, potentially induce bias. The aim of the study was to compare 24-h urine and spot urine sampling and two dilution adjustment techniques, when assessing U-Cd.     

Agreement of pesticide biomarkers between morning void and 24-h urine samples from farmers and their children

In pesticide biomonitoring studies, researchers typically collect either single voids or daily (24-h) urine samples. Collection of 24-h urine samples is considered the "gold-standard", but this method places a high burden on study volunteers, requires greater resources, and may result in misclassification of exposure or underestimation of dose due to noncompliance with urine collection protocols. To evaluate the potential measurement error introduced by single void samples, we present an analysis of exposure and dose for two commonly used pesticides based on single morning void (MV) and 24-h urine collections in farmers and farm children. The agreement between the MV concentration and its corresponding 24-h concentration was analyzed using simple graphical and statistical techniques and risk assessment methodology. A consistent bias towards overprediction of pesticide concentration was found among the MVs, likely in large part due to the pharmacokinetic time course of the analytes in urine. These results suggest that the use of single voids can either over- or under-estimate daily exposure if recent pesticide applications have occurred. This held true for both farmers as well as farm children, who were not directly exposed to the applications. As a result, single void samples influenced the number of children exposed to chlorpyrifos whose daily dose estimates were above levels of toxicologic significance. In populations where fluctuations in pesticide exposure are expected (e.g., farm families), the pharmacokinetics of the pesticide and the timing of exposure events and urine collection must be understood when relying on single voids as a surrogate for longer time-frames of exposure.     

Hippuric acid in 24 h urine collections as a biomarker of fruits and vegetables intake in kidney stone formers

This work aimed to underline the prospects of hippuric acid, a product of the metabolism of polyphenols, as a new biomarker of fruits and vegetables intake associated with lithogenic risk. Biochemical parameters of lithogenic risk and hippuric acid were measured in the 24 h urine collections of a cohort of 696 Italian kidney stone formers divided into two subgroups according to their different dietary habits. The link between lithogenic risk parameters and hippuric acid was assessed and this compound was revealed as a valuable biomarker of fruits and vegetables intake in kidney stone formers. A cut-off value of urinary excretion of hippuric acid, 300?mg/24?h, was set as the threshold of discrimination between low and high intake of fruits and vegetables for these patients. These results highlight the importance of monitoring of the excretion hippuric acid in urine to address proper dietary guidelines for the management of stone former patients.     

The use of sodium para-aminohippurate (PAH) as a marker of the completeness of urine collections: Studies in patients receiving total parenteral nutrition

The completeness of 32 urine collections obtained from 12 patients receiving total parenteral nutrition continuously over 24 h periods was assessed by adding 750 mg and 2 μCi (74 kBq) of ¹⁴C sodium para-aminohippurate monohydrate (PAH) to their infusate and measuring the recovery of these markers in urine. The recovery was found to be 73 ± 3% (SEM) of the administered dose of PAH (in contrast to complete recovery of the marker in normal subjects given a bolus injection). Measurements of nitrogen, calcium and phosphorus in urine samples of the parenterally fed patients, and their calculated balances, were substantially in error. Creatinine excretion expressed as a percentage of the predicted value, varied by as much as 30% for a given degree of PAH excretion. Radionuclide measurements of urinary PAH were compared with colorimetric and chromatographic measurements. Some drugs and their urinary metabolites interfered with the colorimetric measurements, whilst other urinary compounds interfered with the chromatographic measurements. It is suggested that PAH, particularly labelled PAH, is useful for assessing the completeness of urine collections especially in parenterally fed patients participating in metabolic or nutritional studies.     

Variation in plasma cystathionine and its relation to changes in plasma concentrations of homocysteine and methionine in healthy subjects during a 24-h observation period

BACKGROUND: Plasma cystathionine measurement may be a useful complement to total homocysteine measurement in the assessment of B vitamin status. Information on the within-person variation in cystathionine is currently sparse. OBJECTIVE: The goal was to study the daily variation in plasma cystathionine concentrations in healthy subjects. DESIGN: Twelve subjects (aged 22-29 y) were followed for 24 h. During the observation period, the subjects received a breakfast (containing 15-18 g protein) at 0900 and a beef dinner (containing approximately 50 g protein) at 1500. Multiple blood samples for metabolite analyses were collected during the day, and a final sample was obtained the next morning. The results are expressed as medians and interquartile ranges. RESULTS: All subjects had normal fasting cystathionine concentrations [0.120 (0.100-0.160) micro mol/L]. Cystathionine concentrations increased significantly after breakfast, reached a maximum after 4 h of 142.4% (100.0-170.3%) of the fasting concentration, and then declined to fasting concentrations before dinner. After dinner, plasma cystathionine started to increase within 0.5 h and reached a maximum after 6 h [281.3% (194.1-351.4%) of the concentration measured before dinner]. The changes in plasma methionine and total homocysteine concentrations during the day were less pronounced. CONCLUSION: Food intake, even of foods with low protein content, causes an increase in plasma cystathionine concentrations that is more pronounced than the concomitant changes in total homocysteine and methionine. In studies including plasma cystathionine measurement, blood sampling in the fasting state should be considered.