Reduction of reaction differences between human mercaptalbumin and human nonmercaptalbumin measured by the bromcresol purple method

Serum albumin redox state as an indicator of dietary protein intake among community-dwelling older adults

BACKGROUND AND AIMS

Serum markers capable of detecting mild levels of undernutrition, such as insufficient dietary protein intake (IDPI), have not been established among community-dwelling older adults. Although the serum albumin redox state, expressed as the ratio of reduced albumin (Alb) to total Alb (the reduced albumin ratio), has the potential to overcome this challenge, empirical epidemiological data are lacking. This study aimed to investigate the association between a serum reduced Alb ratio and dietary protein intake among community-dwelling older adults.

METHODS

This study analyzed cross-sectional data from 1,005 community dwelling population (572 males and 433 females) aged 70-84 years who participated in the Itabashi Longitudinal Study on Aging. Exclusion criteria included participants with incomplete data, individuals with a history of kidney disease and high C-reactive protein (CRP) levels. The dietary protein intake was estimated using validated food frequency questionnaires. The IDPI was defined as not meeting the level recommended by the Dietary Reference Intakes for Japanese (Men ≥60 g/day, Women ≥50 g/day).

RESULTS

IDPI was observed in 14.1% of the study population. Logistic regression analyses adjusted for sex, age, body weight and malnutrition showed that a serum reduced Alb ratio was significantly associated with IDPI (odds ratio = 0.962, 95% confidence interval = 0.926-0.999), whereas serum albumin concentration was not (odds ratio = 0.549, 95% confidence interval = 0.285-1.061).

CONCLUSIONS

A serum reduced Alb ratio would be a useful indicator of protein insufficiency among community-dwelling older adults.

Quantitation of oxidized and reduced albumin in mammals. An intriguing analytical question

Oxidized albumin is considered a short-term biomarker of oxidative stress and its measurement in blood contributes to evaluate the impact of diseases, drugs, dialytic treatments, physical activity, environmental contaminants etc. on the red-ox balance of humans as well as of other mammalians. Nevertheless, the most common methods for quantifying the oxidized and reduced albumins are costly and time-consuming. Furthermore, there is a dearth of information regarding the proper ways to store human serum or plasma samples in order to prevent inaccurate quantification of these various albumin forms. This paper explores these aspects and proposes a few spectrophotometric assay procedures which make the quantitation of oxidized and reduced albumin very fast, precise and un-expensive in various mammals.

Development and Evaluation of "The Delta Plus-Minus Even Distribution Check": A Novel Patient-Based Real-Time Quality Control Method for Laboratory Tests

BACKGROUND

Laboratory testing of large sample numbers necessitates high-volume rapid processing, and these test results require immediate validation and a high level of quality assurance. Therefore, real-time quality control including delta checking is an important issue. Delta checking is a process of identifying errors in individual patient results by reviewing differences from previous results of the same patient (Δ value). Under stable analytical conditions, Δ values are equally positively and negatively distributed.

METHODS

The previous 20 Δ values from 3 tests (cholesterol, albumin, and urea nitrogen) were analyzed by calculating the R-value: "the positive Δ value ratio minus 0.5." This method of monitoring optimized R-values is referred to as the even-check method (ECM) and was compared with quality control (QC) testing in terms of error detection.

RESULTS

Bias was observed on 4 of the 120 days for the 3 analytes measured. When QC detected errors, the ECM captured the same systematic errors and more rapidly. In contrast, the ECM did not generate an alarm for the one random error that occurred in QC. While QC did not detect any errors, the percentage of R-values exceeding the acceptable range was under 2%, the number of days generating alarms was between 16 and 21 days, with short alarm periods, and a median number of samples per alarm period between 7 and 9 samples.

CONCLUSIONS

The ECM is a practical real-time QC method, controlled by setting R-value conditions, that quickly detects bias values.

Evaluation of the two-point calibration bromocresol green method, showing reduced deviation from the bromocresol purple method in sera from patients with hypoalbuminemia

BACKGROUND

The bromocresol green (BCG) and bromocresol purple (BCP) methods are widely used for albumin measurements in routine testing, but the BCG method is known to react with globulin fractions and to have low specificity for albumin. We evaluated a calibration method using different concentrations of human serum albumin standards (two-point calibration BCG method) with the aim of reducing the effect of globulin fractions on the BCG method in patients with hypoalbuminemia.

METHOD

In the two-point calibration BCG method, two concentrations of standard solutions and their calibration values are set based on the difference in albumin concentrations measured by the BCG method (BCG-HSA method) and the modified BCP (modified BCP-HSA method) calibrated with human serum albumin standard solution (HSA). Albumin concentrations were measured in 136 patient serum samples (healthy group: 52, hypoalbuminemic group: 84) by the two-point calibrated BCG method and compared with those obtained using the modified BCP-HSA method.

RESULTS

The mean albumin concentrations obtained using the two-point calibrated BCG and modified BCP-HSA methods were 39.18 ± 3.42 g/L and 39.37 ± 3.14 g/L (healthy group) and 26.20 ± 6.23 g/L and 26.23 ± 5.67 g/L (hypoalbuminemia group), respectively. The results of the two-point calibration BCG method were in a close agreement over the entire concentration range tested compared to the modified BCP-HSA method.

CONCLUSIONS

Based on these results, this calibration method reduces the influence of the globulin fraction on the BCG method. In the hypoalbuminemic group, the calibration method was shown to provide results consistent with the BCP method, which is highly specific for albumin.

Effect of albumin measurement methods on the albumin-bilirubin grade

BACKGROUND

Albumin-bilirubin (ALBI) grade is an index of liver function based on total bilirubin (T-BIL) and albumin levels, and its usefulness has been widely reported. This study aimed to investigate the effect of different methods of measuring T-BIL and albumin levels on the ALBI grade in patients with liver disease.

METHODS

In total, 170 patients from our hospital were included in this study. Correlations between T-BIL levels measured using the vanadate oxidation and enzymatic methods were analysed. Similarly, a correlation analysis of albumin levels between the bromocresol green (BCG) and modified bromocresol purple (BCP) methods was performed. Additionally, the ALBI grade was calculated for patients with liver disease, and the differences between each method of albumin measurement were compared.

RESULTS

No differences were observed in the measured T-BIL values between the two methods. Contrastingly, the albumin levels of 100 random samples and 70 liver disease patients obtained using the modified BCP method were significantly lower than those measured using the BCG method. The rate of change in the modified ALBI grade between the BCG and BCP methods was 25.7%.

CONCLUSIONS

Caution should be taken when comparing ALBI grades with those measured by other facilities because the method of albumin measurement can affect the ALBI grade. Standardization of albumin measurement is needed worldwide.

A novel method for predicting the unbound valproic acid concentration

In this study, we constructed a prediction formula for unbound valproic acid (VPA) concentration that was more accurate and widely applicable than previously reported formulae. A total of 136 datasets from 75 patients were analyzed retrospectively. The median of free fraction of VPA was 0.16 (interquartile range: 0.07; range: 0.07-0.45). The parameter that combined total VPA concentration (C_tVPA) and serum albumin (SA), (C_tVPA [μM] - 2 × SA [μM]), was significantly related to the free fraction of VPA (r = 0.76, p < 0.001). We constructed a combined parameter-based prediction formula for unbound VPA concentration. Analysis using external datasets from patients without severe renal failure showed that the prediction errors of the unbound VPA concentration were lower than those of previously reported formulae. Although the previous formulae showed large prediction errors, especially in the specific range of C_tVPA values, the constructed formula showed a weak trend with C_tVPA or SA. The formula based on (C_tVPA [μM] - 2 × SA [μM]) had high prediction accuracy and wide applicability in predicting the unbound VPA concentration in patients without severe renal failure.

A simple colorimetric assay to determine the concentration and proportion of human mercaptalbumin

Objectives

Design and methods

Results

Conclusions

•

Concentrations of the reduced form of human serum albumin (human mercaptalbumin) were measured by a colorimetric assay using Michler's Hydrol.

•

The assay uses the total thiol concentration to approximate the human mercaptalbumin concentration.

•

Accuracy was improved by alkylating part of the samples and canceling the contribution of the non-thiol component to the colorimetric changes.

•

Combining Michler's Hydrol assay with bromocresol purple assay enabled us to obtain the proportions of mercaptalbumin and non-mercaptalbumin, which correlated with HPLC as a reference method.

Gestational Age-Dependent Reference Ranges for Albumin Levels in Cord Serum

BACKGROUND

To diagnose hypoalbuminemia in newborns, it is essential to establish a definition applicable to those with a different gestational age (GA) and clinical conditions. A positive correlation between serum albumin levels and GA has been reported, but the study was limited to small numbers of newborns. We therefore investigated the GA-dependent reference ranges for serum albumin levels using cord venous blood (UC-Alb levels) from a large number of newborns delivered at a tertiary perinatal center.

METHODS

Albumin levels were assessed in 2,917 newborns at 22-41 weeks of GA after exclusion of those with congenital disorders. Linear regression analysis was used to correlate GA and UC-Alb levels. After calculation of the percentile values of UC-Alb levels for each week of GA, the distributions were approximated by the least-squares method. To validate the determined linear approximation of the 5%ile value, the UC-Alb levels in newborns with hydrops fetalis and gastroschisis were used.

RESULTS

A significant positive correlation between GA and UC-Alb levels was found (rs = 0.701, p < 0.001, respectively). The distribution of the 5%ile of UC-Alb levels (Y) by GA (X) was approximated as a straight line (Y = 0.062 × X + 0.326, R2 = 0.951). Among the 59 and 18 newborns with hydrops fetalis and gastroschisis, 51 (86.4%) and 15 (83.3%), respectively, were below the line.

CONCLUSIONS

We established GA-dependent reference ranges for serum albumin levels, which may be useful to accurately diagnose hypoalbuminemia in newborns.

Serum Albumin Redox States: More Than Oxidative Stress Biomarker

Serum albumin is the most abundant circulating protein in mammals including humans. It has three isoforms according to the redox state of the free cysteine residue at position 34, named as mercaptalbumin (reduced albumin), non-mercaptalbumin-1 and -2 (oxidized albumin), respectively. The serum albumin redox state has long been viewed as a biomarker of systemic oxidative stress, as the redox state shifts to a more oxidized state in response to the severity of the pathological condition in various diseases such as liver diseases and renal failures. However, recent ex vivo studies revealed oxidized albumin per se could aggravate the pathological conditions. Furthermore, the possibility of the serum albumin redox state as a sensitive protein nutrition biomarker has also been demonstrated in a series of animal studies. A paradigm shift is thus ongoing in the research field of the serum albumin. This article provides an updated overview of analytical techniques for serum albumin redox state and its association with human health, focusing on recent findings.

A Novel Uremic Score Reflecting Accumulation of Specific Uremic Toxins More Precisely Predicts One-Year Mortality after Hemodialysis Commencement: A Retrospective Cohort Study

Uremic toxins (UTs) generally accumulate in patients developing end-stage renal disease (ESRD). Although some kinds of UTs cause early death after starting hemodialysis (HD), it remains unknown whether the degree of excessive accumulation of various UTs is associated with worsening of prognosis. We retrospectively conducted this cohort study consisting of adult patients developing ESRD who initiated HD at the National Center for Global Health and Medicine from 2010 to 2019. We created a new uremic score, which was defined as the aggregate score of the following variables reflecting uremic state: elevated blood urea nitrogen, β2-microglobulin, and anion gap before starting HD. The primary outcome was early mortality within 1-year after HD commencement. The hazard ratio (HR) and 95% confidence interval (CI) for a one-point increase in uremic score was calculated with Cox proportional hazard models adjusted by baseline conditions. We included 230 participants, 16 of whom experienced the primary outcome of early mortality after HD commencement. Uremic score was significantly associated with the primary outcome (crude HR: 1.91, 95% CI 1.16–3.14; adjusted HR: 4.19, 95% CI 1.79–9.78). Our novel uremic score, reflecting accumulation of specific UTs, more precisely predicts early mortality after HD commencement.

Changes in Background Liver Function in Patients with Hepatocellular Carcinoma over 30 Years: Comparison of Child-Pugh Classification and Albumin Bilirubin Grade

BACKGROUND

Background liver function in patients with hepatocellular carcinoma (HCC) has improved remarkably with advances in various treatments. Recently, the Child-Pugh classification (CPC) system has been recognized as limited in its ability to assess patients with good hepatic reserve. We compared the albumin-bilirubin (ALBI) grade, which is suitable for a more detailed evaluation of patients with good liver function, with CPC over a 30-year period.

METHODS

A total of 2,347 patients were analyzed. Patients were stratified by year of diagnosis into 6 groups: Group A (1990-1994, n = 376), Group B (1995-1999, n = 434), Group C (2000-2004, n = 438), Group D (2005-2009, n = 444), Group E (2010-2014, n = 392), and Group F (2015-2018, n = 263). We compared ALBI grade and CPC across the groups.

RESULTS

The prevalence of patients with CPC A at diagnosis increased throughout the study period, reaching nearly 80% in Groups E and F (p < 0.001). By contrast, the percentage of patients with ALBI grade 1 disease remained approximately 50% in Groups E and F (p < 0.001). Modified ALBI (mALBI) grade 2a corresponds to patients with CPC A who have poor hepatic function. There were significant survival differences between patients with mALBI grade 1 versus 2a, 1 versus 2b, and 2a versus 2b disease, respectively (p < 0.0001), in patients with CPC A.

CONCLUSIONS

CPC is not suitable for assessing patients with recently diagnosed HCC and good remnant hepatic function. In such patients with HCC, the prognosis can be stratified by ALBI grade rather than CPC.

New colorimetric method with bromocresol purple for estimating the redox state of human serum albumin

Oxidative damage results in protein modification and is observed in many diseases, such as heart failure and renal insufficiency. Human serum albumin is an index of oxidative change and is conventionally measured using high-performance liquid chromatography (HPLC). Although this method is more sensitive than the colorimetric method, it is time-consuming for clinical practice and the sera must be stored at –80°C before analysis. To overcome these limitations, in the present study we developed a new reagent for a more rapid and convenient quantification of oxidative stress, involving determination of the ratio of human nonmercaptalbumin to total albumin using a colorimetric method with bromocresol purple. The clinical utility of the developed reagent was confirmed by demonstrating the consistently higher oxidative stress levels in dialysis patients than in healthy control subjects, matching the results of the conventional HPLC method. This novel approach could be a valuable tool for immediate estimation of the state of oxidative stress during the course of disease and treatment, and could aid clinical treatment decisions.

A multi-center evaluation of a device for measurement of bilirubin binding capacity in neonates: the effects of gestational age, Intralipid exposure and illness severity

OBJECTIVE

Measure daily bilirubin-binding capacity (BBC) variation using an automated, not as-yet FDA approved, Point-of-Care hematofluorometer. Measure the effects of prematurity, clinical instability and exposure to Intralipid on BBC.

SUBJECTS

Convenience sample of 109 infants from well-baby and intensive care nurseries. Gestational ages 28-41 weeks. 261 specimens obtained from postnatal ages 1-4 days. Unstable neonates were defined by need for at least noninvasive respiratory support and FiO2 ≥ 0.25.

RESULTS

Median interday variation was 2.9 ± 5.1 mg/dL. BBC (0.254 mg/dL/wk) and albumin (0.037 g/dL/wk) increased for each week of gestation. BBC was lower in unstable compared to well infants (26.1 ± 7.6 mg/dL v 28.6 ± 6.3 mg/dL). BBC was not significantly different in infants receiving or not receiving IL.

CONCLUSIONS

BBC measurements using the device had acceptable intraspecimen reproducibility and interday variability. BBC may be helpful in guiding the assessment of aggressive versus conservative management decisions in preterm and sick infants with hyperbilirubinemia.

Evaluation of glycated albumin (GA) and GA/HbA1c ratio for diagnosis of diabetes and glycemic control: A comprehensive review

Diabetes Mellitus (DM) is a group of metabolic diseases characterized by chronic high blood glucose concentrations (hyperglycemia). When it is left untreated or improperly managed, it can lead to acute complications including diabetic ketoacidosis and non-ketotic hyperosmolar coma. In addition, possible long-term complications include impotence, nerve damage, stroke, chronic kidney failure, cardiovascular disease, foot ulcers, and retinopathy. Historically, universal methods to measure glycemic control for the diagnosis of diabetes included fasting plasma glucose level (FPG), 2-h plasma glucose (2HP), and random plasma glucose. However, these measurements did not provide information about glycemic control over a long period of time. To address this problem, there has been a switch in the past decade to diagnosing diabetes and its severity through measurement of blood glycated proteins such as Hemoglobin A1c (HbA1c) and glycated albumin (GA). Diagnosis and evaluation of diabetes using glycated proteins has many advantages including high accuracy of glycemic control over a period of time. Currently, common laboratory methods used to measure glycated proteins are high-performance liquid chromatography (HPLC), immunoassay, and electrophoresis. HbA1c is one of the most important diagnostic factors for diabetes. However, some reports indicate that HbA1c is not a suitable marker to determine glycemic control in all diabetic patients. GA, which is not influenced by changes in the lifespan of erythrocytes, is thought to be a good alternative indicator of glycemic control in diabetic patients. Here, we review the literature that has investigated the suitability of HbA1c, GA and GA:HbA1c as indicators of long-term glycemic control and demonstrate the importance of selecting the appropriate glycated protein based on the patient's health status in order to provide useful and modern point-of-care monitoring and treatment.

Oral branched-chain amino acid granules improve structure and function of human serum albumin in cirrhotic patients

BACKGROUND AND AIMS

The aim of this study was to evaluate structural and functional alterations of human serum albumin (HSA), with a special focus on the oxidized and reduced forms, in patients with chronic liver disease. We also investigated whether oral branched-chain amino acid (BCAA) supplementation could induce structural changes and improve the functions of HSA.

METHODS

The proportion of reduced and oxidized HSA was determined in 16 healthy controls and in 20 chronic hepatitis and 100 cirrhotic patients with stable conditions. To evaluate the functional properties of HSA, this study focused on the antioxidant and binding functions. The radical scavenging activity and binding ability of purified HSA were measured in 68 participants. After BCAA administration for 6 months, 29 patients were evaluated for HSA structural changes, with 19 out of the 29 patients also analyzed for HSA functional changes.

RESULTS

There was a significant decrease in the amounts of reduced HSA in conjunction with liver disease progression. Receiver operating characteristic curve analysis demonstrated that the levels of reduced HSA had high accuracy in determining disease progression. Functional alterations were strongly correlated to the levels of reduced HSA. BCAA supplementation led to substantial increases in the amount of reduced HSA. The altered HSA was able to scavenge significantly more radicals and restore the binding ability.

CONCLUSION

This study describes structural alterations and functional disturbances of HSA in patients with chronic liver disease, and indicates that the levels of reduced HSA might reflect disease progression and the functional properties of HSA. Moreover, oral BCAA supplementation increases the amount of reduced HSA, thereby leading to the restoration of HSA function in cirrhotic patients.

Serum diamine oxidase activity as a predictor of gastrointestinal toxicity and malnutrition due to anticancer drugs

BACKGROUND AND AIM

Objective evaluation of intestinal mucosal damage due to anticancer drugs is generally difficult. Serum diamine oxidase (DAO) activity is reported to reflect the integrity and maturity of the small intestinal mucosa. Therefore, we investigated whether serum DAO activity is an indicator of gastrointestinal toxicity or nutritional status in patients receiving chemotherapy.

METHODS

We prospectively enrolled 20 patients with unresectable metastatic gastric cancer who received oral S-1 (80 mg/m(2) ) on days 1-14, and intravenous cisplatin (60 mg/m(2) ) and docetaxel (50 mg/m(2) ) on day 8 every 3 weeks. Serum DAO activity was measured by colorimetry. Gastrointestinal toxicity was evaluated by Common Toxicity Criteria for Adverse Events version 4.0. Endoscopic examination and biopsy of duodenal mucosa assessed mucosal damage. Malnutrition was evaluated by measuring serum total protein and albumin levels.

RESULTS

Serum DAO activity decreased step-by-step significantly during anticancer drug treatment and recovered after drug holidays. In all 14 patients who experienced diarrhea, serum DAO activity significantly decreased prior to diarrhea onset. Percent decrease in DAO activity was significantly correlated with severity of diarrhea. Significant correlation was observed between percent decrease in DAO activity and percent decrease in duodenal villus height or surface area from baseline. There were also significant correlations between percent decrease in serum DAO activity at day 14 and percent decrease in serum total protein or albumin levels at day 21 from baseline.

CONCLUSION

Serum DAO activity sensitively indicates gastrointestinal damage prior to symptom onset and can be a useful predictor of intestinal mucosal damage and nutritional status in patients receiving chemotherapy.

The bromocresol green assay, but not the modified bromocresol purple assay, overestimates the serum albumin concentration in nephrotic syndrome through reaction with α2-macroglobulin

Background

The bromocresol green (BCG) assay is commonly used for measuring albumin (ALB), but is affected by α1- and α2-globulins, which are elevated in systemic inflammation. The modified bromocresol purple (mBCP) assay is another dye-binding method developed to overcome non-specific reactions. Concentrations of α2-macroglobulin, a major α2-globulin component, are increased in nephrotic syndrome (NS), but not in inflammation. There is little direct evidence that α2-macroglobulin affects BCG or mBCP assays.

Methods

We measured serum albumin concentrations in 33 patients with NS and 13 reference healthy controls using BCG (ALBBCG) and mBCP (ALBmBCP) assays, and nephelometry (nALB) as a reference method. We also determined five specific proteins belonging to the α1- and α2-globulins by nephelometry. After adding purified α2-macroglobulin to albumin solutions, protein reactivity in these three assays was compared.

Results

Nephrotic syndrome patients were categorized to tertiles according to nALB concentration. In all tertiles, ALBBCG was significantly higher than nALB, especially in the severe hypoalbuminemia group, in which α2-macroglobulin was 43–49% higher. By contrast, ALBmBCP and nALB were almost identical in all three groups. The difference between ALBBCG and nALB was positively correlated with the α2-macroglobulin concentration. In vitro, when α2-macroglobulin was added to solutions containing identical albumin concentrations, α2-macroglobulin dose-dependently increased ALBBCG, but not ALBmBCP.

Conclusions

In NS, α2-macroglobulin is a major factor for positive bias of ALBBCG, especially in patients with severe hypoalbuminemia. The mBCP assay is useful for measuring albumin concentrations in NS.

Serum albumin-adjusted glycated albumin is a better indicator of glycaemic control in diabetic patients with end-stage renal disease not on haemodialysis

Backgrounds

Diabetic patients with end-stage renal disease who are not on haemodialysis show low concentrations of HbA1c and glycated albumin due to renal anaemia and proteinuria, respectively. In the present study, we examined whether serum albumin-adjusted glycated albumin could accurately reflect glycaemic control in these patients.

Methods

To examine the correlation between glycated albumin and serum albumin (Study 1), 49 diabetic patients with end-stage renal disease not on haemodialysis were used. To evaluate the association between the glycaemic control indicators and the glycaemic control state (Study 2), 30 diabetic patients with end-stage renal disease were enrolled. The estimated HbA1c and the estimated glycated albumin concentrations were calculated based on the mean blood glucose concentrations obtained from the diurnal variation. The adjusted glycated albumin concentrations were calculated from the regression formula between the serum albumin and glycated albumin obtained from Study 1.

Results

No significant correlation was found between the measured HbA1c and estimated HbA1c concentrations. The estimated HbA1c (inversely) and measured HbA1c/estimated HbA1c ratio (positively), but not measured HbA1c, showed a significant correlation with Hb concentrations. The estimated glycated albumin was positively associated with the measured glycated albumin and adjusted glycated albumin concentrations. Although measured glycated albumin/estimated glycated albumin ratio was positively correlated with serum albumin, there was no significant association between the adjusted glycated albumin/estimated glycated albumin ratio and serum albumin, Hb and estimated glomerular filtration rate.

Conclusions

We found for the first time that the adjustment of glycated albumin by serum albumin could be useful to determine glycaemic control in diabetic patients with end-stage renal disease not on haemodialysis. These findings suggest that adjusted glycated albumin might be a better indicator of glycaemic control than measured HbA1c and measured glycated albumin in these patients.

A revised method for determination of serum mercaptalbumin and non-mercaptalbumin by high-performance liquid chromatography coupled with postcolumn bromocresol green reaction

BACKGROUND

Previously, high-performance liquid chromatography (HPLC) equipped with ultraviolet or fluorescence detectors has been used for separation of human mercaptalbumin (HMA) and human non-mercaptalbumin (HNA). However, it is difficult to perform reliable chromatographic analysis due to peak interference of such serum compounds as uric acid and bilirubin. The aim of this study is to explore a selective and simple analytical method for the determination of HMA and HNA.

METHOD

HMA and HNA in serum sample were separated by HPLC and reacted with bromocresol green using a postcolumn reaction scheme.

RESULTS

A complete separation of HMA and HNA is achieved in less than 30 min by using weak anion exchange columns and isocratic elution. Within-run and between-day precisions at albumin concentration of 45 g/L were 4.2 and 1.7% for HMA and 4.5 and 4.6% for HNA, respectively. There was no interference in HMA and HNA peaks when bilirubin-, haemoglobin- or chyle-spiked pooled serum samples were analysed.

CONCLUSION

Our method is reliable and not labour-intensive and, therefore, might be applicable for clinical and epidemiological studies.

Postnatal serum concentrations of endogenous free fatty acids in newborns admitted to the neonatal intensive care unit: effects on unbound bilirubin

Background

Few studies have reported the characterization of postnatal serum concentrations of endogenous free fatty acids (FFAs) in high-risk newborns and their effects on unbound bilirubin (UB).

Methods

Serum concentrations of FFA, albumin (Alb), UB and total bilirubin (TB) were measured in 713 samples obtained within 5 days after birth from 439 newborns without intravenous lipid supplementation admitted to the neonatal intensive care unit (NICU). Serum FFA was reported as the day-specific percentile-based curve. Serum FFA and FFA/Alb ratios were compared in term and preterm patients. To assess the impact of FFA on UB, daily changes in FFA/Alb and UB/TB ratios were compared in term patients without receiving phototherapy or any drugs, and linear regression analysis was performed between FFA/Alb ratio and serum UB concentration or UB/TB ratio using 140 sera with hyperbilirubinemia of term and preterm patients.

Results

A percentile-based curve showed that serum FFA peaked at 1 day of age and progressively decreased. Serum FFA and the FFA/Alb ratio were significantly higher in term than in preterm patients at birth and 1 and 3 days of age. FFA/Alb ratio significantly changed over 5 days after birth, but UB/TB ratio remained constant. FFA/Alb ratio did not correlate with serum UB concentration or UB/TB ratio in sera with hyperbilirubinemia.

Conclusions

We assessed postnatal concentrations of serum FFA in a large number of high-risk newborns admitted to the NICU. The concentration of endogenous FFAs in newborns admitted to the NICU was not rising until it influenced UB.

Albumin concentration determined by the modified bromocresol purple method is superior to that by the bromocresol green method for assessing nutritional status in malnourished patients with inflammation

BACKGROUND

The controlling nutritional status (CONUT) score (CS), a simple score for assessing nutritional status, is calculated using laboratory data, including serum albumin concentration. Although dye-binding assays such as the bromocresol green (BCG) and modified bromocresol purple (mBCP) methods are widely used for albumin measurement, acute-phase proteins interfere with the BCG method.

OBJECTIVE

We aimed to determine whether the choice of albumin assay affects assessment of nutritional status using CONUT scores (CSs).

DESIGN

We measured serum albumin concentrations by the BCG (ALBBCG) and mBCP (ALBmBCP) methods in 44 malnourished inpatients, 27 of whom underwent nutritional intervention, and compared them to 30 age-matched healthy volunteers. In treated patients, CSs were calculated by ALBBCG (CS-BCG) and ALBmBCP (CS-mBCP).

RESULTS

C-reactive protein (CRP) concentrations were positively correlated with the difference between ALBBCG and ALBmBCP in malnourished inpatients (r = 0.59, p < 0.001). CS-BCG was always lower than CS-mBCP (lower CS indicates superior nutritional status) in treated patients with persistently high CRP levels. However, in patients whose CRP decreased gradually, this difference diminished over the clinical course. CS-BCG and CS-mBCP were similar throughout their courses in patients with normal CRP concentrations. Adding haptoglobin to the human albumin solutions increased ALBBCG in a dose-dependent manner.

CONCLUSIONS

The choice of albumin assay affected the assessment of nutritional status using CSs in patients with inflammation. We recommend that the modified BCP assay be used to assess nutritional status, particularly in patients with inflammation.

Is bilirubin/albumin ratio correlated with unbound bilirubin concentration?

BACKGROUND

The American Academy of Pediatrics guidelines recommend that the total bilirubin (TB)/albumin (Alb) ratio (B/A ratio), instead of serum concentration of unbound bilirubin (UB), can be used with TB for determining treatment modality for jaundiced newborns ≥ 35 weeks of gestation. It is unknown, however, whether the B/A ratio is actually correlated with serum UB.

METHODS

Four hundred and ninety-seven serum samples were obtained from 209 newborns ≥ 35 weeks of gestation, who were admitted to Kobe University Hospital. Serum UB concentration was measured using the glucose oxidase-peroxidase method. Serum TB and Alb concentrations were measured on spectrophotometry. B/A ratios were calculated and were linearly compared with serum UB. Furthermore, the accuracy of the B/A ratio was evaluated.

RESULTS

The B/A ratio was significantly correlated with serum UB concentration. A serum UB concentration of 0.6 µg/dL was in agreement with a B/A ratio of 0.5. For comparison of the number of newborns who had serum UB concentrations ≥ or <0.6 µg/dL and B/A ratios ≥ or <0.5, we found the following characteristics: the concordance rate between serum UB concentrations and the B/A ratio was 94%, sensitivity was 51%, and specificity was 99%.

CONCLUSIONS

The B/A ratio is significantly correlated with serum UB concentration in newborns ≥ 35 weeks of gestation. The B/A ratio, however, is underestimated when serum UB concentrations are >0.6 µg/dL.

Basic performance of an enzymatic method for glycated albumin and reference range determination

BACKGROUND

Glycated albumin (GA) is a medium-term glycemic control marker of diabetes and may be more sensitive to changes in plasma glucose than hemoglobin A1c. We studied where and how many fructosyl groups bind to albumin, and which glycation sites are measured by the enzymatic method for GA. We also studied the basic performance of the enzymatic method for GA.

METHODS

Glycated albumin was measured using an enzymatic method (Lucica®GA-L, Asahi Kasei Pharma) on a biochemical autoanalyzer. Molecular weights of purified GA and nonglycated albumin were measured by a mass spectrometry system. Two hundred one healthy volunteers with normal results of oral glucose tolerance testing were recruited to determine the reference range in Americans.

RESULTS

The present method measured only glycated amino acids from albumin in serum protein. We estimate that the number of glycated amino acids measured by this method was approximately two per molecule of albumin. The general performance (sensitivity, specificity, reproducibility, linearity, interference) of the method was good. The reference range of GA% in Americans with normal glucose tolerance was determined to be 11.9-15.8% (mean ± 2 standard deviations). Significant differences were not observed between the sexes; however, race differences were observed (higher levels in blacks relative to whites).

CONCLUSIONS

The method was specific for measuring glycated amino acids in albumin and had good basic performance characteristics. The reference range in Americans was 11.9-15.8%. This method may be a useful indicator for diabetes control.

Comparison of glycated albumin and hemoglobin A1c concentrations in diabetic subjects on peritoneal and hemodialysis

BACKGROUND

Relative to hemoglobin A(1c) (HbA(1c)), percentage of glycated albumin (GA%) more accurately reflects recent glycemic control in diabetic hemodialysis (HD) patients.

METHODS

To determine the accuracy of glycemic assays in a larger sample including patients on peritoneal dialysis (PD), HbA(1c) and GA% were measured in 519 diabetic subjects: 55 on PD, 415 on HD, and 49 non-nephropathy controls.

RESULTS

Mean +/- SD serum glucose levels were higher in HD and PD patients relative to non-nephropathy controls (HD 169.7 +/- 62 mg/dL, PD 168.6 +/- 66 mg/dL, controls 146.1 +/- 66 mg/dL; p = 0.03 HD vs controls, p = 0.13 PD vs controls). GA% was also higher in HD and PD patients (HD 20.6% +/- 8.0%, PD 19.0% +/- 5.7%, controls 15.7% +/- 7.7%; p < 0.02 HD vs controls and PD vs controls). HbA(1c) was paradoxically lower in dialysis patients (HD 6.78% +/- 1.6%, PD 6.87% +/- 1.4%, controls 7.3% +/- 1.4%; p = 0.03 HD vs controls, p = 0.12 PD vs controls). The serum glucose/HbA(1c) ratio differed significantly between dialysis patients and controls (p < 0.0001 HD vs controls, p = 0.002 PD vs controls), while serum glucose/GA% ratio was similar across groups (p = 0.96 HD vs controls, p = 0.64 PD vs controls). In best-fit multivariate models with HbA(1c) or GA% as outcome variable, dialysis status was a significant predictor of HbA(1c) but not GA%.

CONCLUSIONS

The relationship between HbA(1c) and GA% differs in diabetic patients with end-stage renal disease who perform either PD or HD compared to those without nephropathy. HbA(1c) significantly underestimates glycemic control in peritoneal and hemodialysis patients relative to GA%.

Physiological and pathological changes in the redox state of human serum albumin critically influence its binding properties

Binding and transport of a number of endogenous and exogenous compounds is an important function of the main plasma protein, albumin. In vivo and in vitro, albumin may be oxidatively modified in different ways with different agents at different sites. These modifications have various consequences on the physiological functions of albumin. Diabetes mellitus, liver diseases and nephropathy are just a few examples of disorders in which oxidative stress is involved and altered albumin functions have been described. This review is focussed on the consequences of oxidative modification on the binding properties of albumin. These range from no effect to decreased or increased binding affinities depending on the ligand under investigation and the type of modification. Indicators for modification include glycosylation, disulphide formation or the content of carbonyl groups. The redox state of albumin can affect the binding properties in several ways, including altered conformation and consequently altered affinities at binding sites and altered binding when the binding reaction itself is redox sensitive. The physiological or pathophysiological concentrations of different oxidatively modified albumin molecules vary over a wide range and are crucial in assessing the clinical relevance of altered ligand binding properties of a particularly modified albumin species in various disease conditions.

Protein Error of pH Indicators in the Presence of Detergents

The characteristics of color development due to a protein error in the dye-binding method in the presence of a non-ionic detergent has been investigated by the calculations based on the chemical equilibrium of a protein error. The calculation results were compared with those obtained using three pH indicators (Bromophenol Blue, Bromocresol Green and Bromocresol Purple) and three non-ionic detergents in the pH region from 1 to 13. In the experiments, the color development increased with the lower concentrations of the detergents, but decreased at higher concentrations. The pH where the color development reached a maximum value shifted to a higher pH as the detergent was added. These experimental results were reproduced by the calculation when the molar absorptivity of the dye-protein complex was assumed to increase due to adding the detergent. Such agreement between the experimental and the calculated results indicates that the characteristics of the color development in the dye-binding method in the presence of a non-ionic detergent can be analyzed by calculations based on the chemical equilibrium of a protein error.

Characteristics of a protein error in determination of serum protein in the presence of inorganic salt

There is a possibility that the color development of the dye-binding method based on a protein error of a pH indicator is affected by the coexisting inorganic salt. Thus, the author theoretically and experimentally investigated the effect of the inorganic salt on the protein error. In a theoretical analysis, the anion of an inorganic salt, like the dissociated dye and buffer anions, was assumed to react with the protein, forming a colorless anion-protein complex. The calculated results were compared with those obtained by experiments using three pH indicators and various kinds of inorganic salts. The calculated results obtained are as follows: (1) The color development decreases with increasing the concentration of the inorganic salt and the equilibrium constant of the reaction between the inorganic salt and protein; (2) The rate of the absorbance decrease is larger for a lower concentration of the inorganic salt than for a higher one; (3) The larger is the equilibrium constant, the larger is the absorbance decrease. The absorbance decrease was caused by the anion, and was increased by increasing the anion concentration. The magnitude of the effect of the anion was iodide > bromide > chloride, which was associated with their ionic radius. The difference in the effect of the anion was thought to indicate that the equilibrium constant, in other words, the bonding strength of the anion to protein is iodide > bromide > chloride.

Problems in serum albumin measurement and clinical significance of albumin microheterogeneity in cirrhotics

OBJECTIVES

To clarify problems with the determination of serum albumin levels, the definition of hypoalbuminemia, and the implications of microheterogeneity of albumin, serum albumin was measured by using dye-binding methods and the authentic method (immunoassay) in patients with liver cirrhosis and healthy subjects.

METHODS

We enrolled 103 patients with liver cirrhosis and 36 healthy subjects. Serum albumin levels were analyzed by immunoassay and the bromcresol green and bromcresol purple methods. Oxidized albumin and glycoalbumin were determined by high-performance liquid chromatography.

RESULTS

In cirrhotic patients, serum albumin levels measured by the bromcresol green method was about 0.2 g/dL higher than that by immunoassay. Serum albumin levels measured by the bromcresol purple method also was higher in cirrhotic patients than those measured by immunoassay and varied widely. In addition, extensive variation was found across serum albumin levels determined by the bromcresol green method at individual institutions (five university hospitals) and those determined by immunoassay at a contract laboratory. The percentages of oxidized albumin and glycoalbumin within total serum albumin increased with progression of liver disease. Further, an increase in oxidized albumin led to an increase in the albumin level as measured by the bromcresol purple method.

CONCLUSION

These results show that adequate assessment of the pathophysiology and prognosis of patients with liver cirrhosis and the efficacy of treatment is not possible with dye-binding methods for determination of serum albumin. Further, the conventional definition of hypoalbuminemia as a serum albumin level of 3.5 g/dL or lower should be reconsidered, and the clinical implications of qualitative changes in albumin should be investigated in consideration of the microheterogeneity of albumin, such as oxidized albumin and glycoalbumin.

Theoretical Analysis Concerning the Characteristics of a Dye-binding Method for Determining Serum Protein Based on Protein Error of pH Indicator: Effect of Buffer Concentration of the Color Reagent on the Color Development

In the dye-binding method based on protein error of a pH indicator, the color development has been reported to be markedly affected by the buffer concentration of the color reagent. In this study, the author analyzed this phenomenon by a theoretical calculation based on the chemical equilibrium of protein error. The calculation was performed on the assumption that both the dissociated dye anion and the anion contained in the buffer solution react with protein, forming a dye-protein complex and an anion-protein complex, respectively. The calculated results were compared with those obtained by the experiments using bromophenol blue, bromocresol green and bromocresol purple that are employed widely for determining the human serum albumin concentration clinically. The calculated results of this method are summarized as follows: (1) the color development decreases with the increase in the concentration of the anion contained in the buffer solution; (2) the calibration curve is more linear in the higher concentration of the anion than in the lower one. These calculated results agreed well with the experimental ones. From these results, it was concluded that the change in the color development by the buffer concentration of the color reagent is due to the change in the concentration of the buffer anion.

Antioxidant capacities of ascorbic acid, uric acid, alpha-tocopherol, and bilirubin can be measured in the presence of another antioxidant, serum albumin

Human serum contains several antioxidants. The total antioxidant capacity (AOC) is the sum of all the antioxidant activities present in serum. The aim of our study was to investigate whether the AOC of bilirubin (BR), alpha-tocopherol (TOH), ascorbic acid (AA), and uric acid (UA) could be measured with good precision and recovery in the presence of human serum albumin (HSA). We measured the AOC of each antioxidant using a Cobas Mira S instrument (Roche Diagnostic Systems, Montclair, NJ) by measuring the inhibitory effect of a given compound on the oxidation of the radical cations of 2,2'-azino-di-(3-ethylbenzthiazoline 6-sulphonate) (ABTS) incubated with metmyoglobin and H(2)O(2). The assay had a linear AOC response range of 27-2,000 micromol/L. The within- and between-day coefficients of variation (CVs) did not exceed 3.4% and 4.2%, respectively. The AOC of albumin in serum is much greater than that of BR, TOH, AA, or UA owing to the substantially greater concentration of HSA in serum. An aliquot of a solution of AA, UA, BR, or TOH was added to HSA or distilled water, and the AOC was determined. The AOC of BR, TOH, AA, and UA increased in a linear way with increasing concentrations. However, we found that the magnitude of increase in the AOC of a mixture of HSA and any of these antioxidants was lower than the sum of the AOC of HSA and any one of the following: AA, UA, BR, or TOH (all expressed in micromol/L).

The Upper Limit pH in the Dye-binding Method for the Determination of Serum Protein via Measurements of the Absorbance Increase Produced by Protein Error

In the dye-binding method for determining the albumin concentration, the absorbance increase due to the change of the color shade by protein error of a pH indicator can be measured by a spectrophotometer. This absorbance increase is observed only in a restricted pH region, but this pH region is not theoretically studied yet. Thus, the author investigated the upper limit pH (pHUL) at which the absorbance increase occurs by the theoretical calculation, and compared these results with those obtained experimentally using four pH indicators. The pHUL is not affected by the dye or protein concentrations, or by the formation constant of the dye-protein complex; but the value changes according to the acid-dissociation constant of the dye (KD) and the ratio of the molar absorptivities of the proton-dissociated dye anion (epsilonD) and the dye-protein complex (epsilonPD). The pHUL value can be calculated by the equation, found theoretically. The calculated pHUL values of BPB, BCG, BCP and BTB were 5.1, 4.8, 6.2 and 5.5, respectively. These values correlated with the experimental results of 4.5 for BPB, 4.7 for BCG, 5.9 for BCP and 5.2 for BTB, but were not associated with the pKD values of each dye. The pHUL of these dyes did not change significantly for various dye and protein concentrations, as was expected from the thoretical calculation.