Underestimation of serum albumin by the bromcresol purple method and a major endogenous ligand in uremia

The different serum albumin assays influence calcium status in haemodialysis patients: a comparative study against free calcium as a reference method

OBJECTIVES

Accurate assessment of calcium levels is crucial for optimal management of regular Haemodialysis (HD) patients. Different calcium adjustment equations and albumin methods; including bromocresol purple (BCP) and bromocresol green (BCG) assays are employed by laboratories, which cause considerable discrepancies between reported results. The aim of this study is to assess the influence of albumin assays on calcium status in stable haemodialysis patients against free calcium (fCa) as a gold standard test.

METHODS

A total of 103 paired serum and fCa samples were collected from a cohort of stable HD patients. Albumin levels were measured by either the BCP or BCG method, and samples were also analysed for the total calcium (T.Ca), phosphate, bicarbonate, and pH levels. The performance of BCG-based and BCP-based adjusted calcium equations was compared using Z-scores scatter plots, intraclass correlation coefficient and Cohen Kappa statistic, with fCa being the reference standard.

RESULTS

Unadjusted T.Ca achieved a 70 % overall classification agreement with fCa and identified 61 % of the "true" hypocalcaemic samples. Adjusted calcium concentrations, calculated by either BCP- or BCG-based equation, were poor predictors of fCa; with more than 50 % of the hypocalcaemic samples being misclassified as normocalcaemic. Notably, both equations misclassified the calcium status in 5 (4.9 %) patients with severe hypocalcaemia (i.e., potentially requiring calcium infusion) as mild hypocalcaemia.

CONCLUSIONS

Our study showed evidence of hidden hypocalcaemia being missed by the current practice of using adjusted calcium in HD patients. Therefore, we recommend abandoning the adjustment procedure in samples from stable HD patients in favour of fCa measurement.

[Albumin adjustment of total serum calcium - is it worth doing?]

Calcium is the most abundant mineral in the human body. About 99% of calcium is deposited in the bones in the form of hydroxyapatite and only 1% is located in the intracellular and extracellular fluid. Ionized calcium, which makes up about 50% of the total amount of circulating calcium, is biologically active; the remaining percentage is bound to plasma proteins (40%, of which albumin accounts for 90%, and globulins for 10%), or is in complex with anions (10%) such as citrate, lactate, bicarbonate, phosphate. Hypo- and hypercalcemia are common conditions treated by physicians of various specialities. Primary hyperparathyroidism and malignant tumors are the most common causes of hypercalcemia, whereas hypocalcemia is most often caused by hypoparathyroidism, malabsorption, vitamin D deficiency or chronic kidney disease. The interpretation of blood calcium concentration results affects the correct diagnosis, the need for further examination, and the choice of treatment. Concentration of ionized calcium is considered a more accurate indicator of the true status of calcemia compared to the concentration of total calcium, but its measurement is difficult due to strict preanalytical and analytical requirements. In the mid-1970s, calcium adjustment equations appeared, which are widely used today. However, some studies have expressed doubts about the sufficient reliability and sensitivity of the corresponding adjustment formulas. The diagnostic accuracy of widely used correction formulas in some clinical situations is lower than the diagnostic accuracy of uncorrected total calcium. The review discusses the history of the formulas for correcting total calcium for albumin, the factors influencing the result of correction, as well as its suitability in various conditions.

Performance evaluation of different albumin assays for the detection of analbuminemia

Analbuminemia is characterized by the near absence of albumin in the plasma. Different methods are available for measuring albumin levels, but they do not necessarily agree with one another. It is a concern that analbuminemic samples could be falsely characterized due to the incorrect estimation of albumin. The objective of the work was to evaluate the performance of different assays in detecting analbuminemia. Albumin knockout (Alb-/-) mouse plasma was used to test the suitability of different albumin assays for their ability to properly characterize extreme albumin deficiency. Bromocresol green (BCG), bromocresol purple (BCP), enzyme-linked immunosorbent assay (ELISA), liquid chromatography-tandem mass spectrometry (LC-MS/MS), and gel electrophoresis were tested. The LC-MS/MS assay exhibited broad coverage of the amino acid sequence of albumin and indicated 8,400-fold lower (P<0.0001) albumin expression in Alb-/- than wildtype (WT), demonstrating its suitability for identifying extreme albumin deficiency. ELISA estimated albumin at 1.5±0.1 g/dL in WT and was below the detection limit in all Alb-/- samples. Gel electrophoresis yielded consistent results with LC-MS/MS and ELISA. The BCG assay overestimated albumin with apparently appreciable albumin concentrations in Alb-/- mice, yet the assay still indicated a significant difference between genotypes (Alb-/-, 1.2±0.05 g/dL, WT, 3.7±0.1 g/dL, P<0.0001). BCP drastically overestimated albumin and could not successfully identify the known analbuminemic phenotype of Alb-/- mice. By using Alb-/- plasma as a reference material and LC-MS/MS as a reference method, ELISA and gel electrophoresis appear appropriate for identifying analbuminemia, while BCG and BCP are not suitable. It is concluded that dye-binding assays should be avoided when extreme hypoalbuminemia or analbuminemia is suspected.

Albumin determined by bromocresol green leads to erroneous results in routine evaluation of patients with chronic kidney disease

OBJECTIVES

Measurement of plasma albumin is pivotal for clinical decision-making in patients with chronic kidney disease (CKD). Routinely used methods as bromocresol green (BCG) and bromocresol purple (BCP) can suffer from aselectivity, but the impact of aselectivity on the accuracy of plasma albumin results of CKD-patients is still unknown. Therefore, we evaluated the performance of BCG-, BCP- and JCTLM-endorsed immunological methods in patients with various stages of CKD.

METHODS

We evaluated the performance of commonly used albumin methods in patients with CKD stages G1 through G5, the latter divided in two groups based on whether they received hemodialysis treatment. In total, 163 patient plasma samples were measured at 14 laboratories, on six different BCG and BCP-platforms, and four different immunological platforms. The results were compared with an ERM-DA-470k-corrected nephelometric assay. The implications on outcome is evaluated by the proportion of patient results <38 g/L for the diagnosis of protein energy wasting.

RESULTS

Albumin results determined with BCP- and immunological methods showed the best agreement with the target value (92.7 and 86.2 %, respectively vs. 66.7 % for BCG, namely due to overestimation). The relative agreement of each method with the target value was platform-dependent, with larger variability in agreement between platforms noted for BCG and immunological methods (3.2-4.6 and 2.6-5.3 %) as opposed to BCP (0.7-1.5 %). The stage of CKD had similar effects on the variability in agreement for the three method-groups (0.6-1.8 % vs. 0.7-1.5 % vs. 0.4-1.6 %). The differences between methods cause discrepancies in clinical decision-making, as structurally fewer patients were diagnosed with protein energy wasting upon using BCG-based albumin results.

CONCLUSIONS

Our study shows that BCP is fit for the intended use to measure plasma albumin levels in CKD patients from all stages, including patients on hemodialysis. In contrast, most BCG-based platforms falsely overestimate the plasma albumin concentration.

Measurement of serum albumin in nephrology: we need to improve

Serum albumin is a widely used biomarker in clinical nephrology. Serum albumin cut-off values are used to define disease, to predict outcome, and to guide patient care. The available commercial assays to measure serum albumin rely on different analytical principles, all with their own (analytical) specifications. This paper provides an overview of the different clinical applications of serum albumin measurements in nephrology, the (dis)advantages of the available assays and the estimates of the effects of the measurement uncertainty between different assays in clinical decision making. This paper concludes that harmonisation of serum albumin assay results are needed.

Role of Albumin Assay on Calcium Levels and Prescription of Phosphate Binders in Chronic Hemodialysis Patients

BACKGROUND/AIMS

In hemodialysis (HD) patients, the bromcresol green (BCG) assay overestimates, whereas the bromcresol purple (BCP) assay underestimates albumin concentration. Since corrected calcium concentrations depend on albumin, the albumin assay may have implications for the management of bone mineral disorders.

METHODS

A subset of patients from CONTRAST, a cohort of prevalent HD patients, was analyzed. Bone mineral parameters and prescription of medication were compared between patients in whom albumin was assessed by BCP versus BCG.

RESULTS

Albumin was assessed by BCP in 331 patients (9 of 25 centers) and by BCG in 175 patients (16 of 25 centers). Albumin was the lowest in the BCP group (34.5 ± 4.2 vs. 40.3 ± 3.1 g/L; p < 0.0005). Measured calcium levels and the prescription of calcium-based phosphate binders were similar in both groups. Corrected calcium levels, however, were markedly higher in the BCP group (2.45 ± 0.18 vs. 2.33 ± 0.18 mmol/L; p < 0.0005).

CONCLUSION

These findings suggest that calcium levels are not corrected for albumin in clinical practice when considering the prescription of calcium-free or calcium-based phosphate-binders in dialysis patients.

Binding of bromocresol green and bromocresol purple to albumin in hemodialysis patients

Background:

Colorimetric albumin assays based on binding to bromocresol purple (BCP) and bromocresol green (BCG) yield different results in chronic kidney disease. Altered dye binding of carbamylated albumin has been suggested as a cause. In the present study, a detailed analysis was carried out in which uremic toxins, acute phase proteins and Kt/V, a parameter describing hemodialysis efficiency, were compared with colorimetrically assayed (BCP and BCG) serum albumin.

Methods:

Albumin was assayed using immunonephelometry on a BN II nephelometer and colorimetrically based on, respectively, BCP and BCG on a Modular P analyzer. Uremic toxins were assessed using high-performance liquid chromatography. Acute phase proteins (C-reactive protein and α1-acid glycoprotein) and plasma protein α2-macroglobulin were assayed nephelometrically. In parallel, Kt/V was calculated.

Results:

Sixty-two serum specimens originating from hemodialysis patients were analyzed. Among the uremic toxins investigated, total para-cresyl sulfate (PCS) showed a significant positive correlation with the BCP/BCG ratio. The serum α1-acid glycoprotein concentration correlated negatively with the BCP/BCG ratio. The BCP/BCG ratio showed also a negative correlation with Kt/V.

Conclusions:

In renal insufficiency, the BCP/BCG ratio of serum albumin is affected by multiple factors: next to carbamylation, uremic toxins (total PCS) and α1-acid glycoprotein also play a role.

Effect of increasing dietary fiber on plasma levels of colon-derived solutes in hemodialysis patients

BACKGROUND AND OBJECTIVES

Numerous uremic solutes are derived from the action of colon microbes. Two such solutes, indoxyl sulfate and p-cresol sulfate, have been associated with adverse outcomes in renal failure. This study tested whether increasing dietary fiber in the form of resistant starch would lower the plasma levels of these solutes in patients on hemodialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Fifty-six patients on maintenance hemodialysis were randomly assigned to receive supplements containing resistant starch (n=28) or control starch (n=28) daily for 6 weeks in a study conducted between October 2010 and May 2013. Of these, 40 patients (20 in each group) completed the study and were included in the final analysis. Plasma indoxyl sulfate and p-cresol sulfate levels were measured at baseline and week 6.

RESULTS

Increasing dietary fiber for 6 weeks significantly reduced the unbound, free plasma level of indoxyl sulfate (median -29% [25th percentile, 75th percentile, -56, -12] for fiber versus -0.4% [-20, 34] for control, P=0.02). The reduction in free plasma levels of indoxyl sulfate was accompanied by a reduction in free plasma levels of p-cresol sulfate (r=0.81, P<0.001). However, the reduction of p-cresol sulfate levels was of lesser magnitude and did not achieve significance (median -28% [-46, 5] for fiber versus 4% [-28, 36] for control, P=0.05).

CONCLUSIONS

Increasing dietary fiber in hemodialysis patients may reduce the plasma levels of the colon-derived solutes indoxyl sulfate and possibly p-cresol sulfate without the need to intensify dialysis treatments. Further studies are required to determine whether such reduction provides clinical benefits.

Magnetic susceptibility to measure total protein concentration from NMR metabolite spectra: Demonstration on blood plasma

PURPOSE

Accurate metabolite and protein quantification in blood plasma and other body fluids from one single NMR measurement, allowing for improved quantitative metabolic profiling and better assessment of metabolite-protein interactions.

THEORY AND METHODS

The total protein concentration is derived from the common chemical-shift changes-caused by protein-induced bulk magnetic susceptibility (BMS)-measured on well-accessible and exchange-free metabolite resonances. These BMS shifts are simply obtained by external referencing with respect to 3-(trimethylsilyl)propionic-2,2,3,3-d4 acid, sodium salt in a coaxial insert.

RESULTS

Based on blood-plasma data from five volunteers, the estimated accuracy of the BMS method is ≤ 5% with respect and comparable to the 3.8% error of the standard colorimetric, Biuret, method. Valine, alanine, glucose, leucine, and lactate display no exchange-induced shift changes. Their well-accessible signals act as reliable probes for pure protein-induced BMS. The slopes and intercepts of their chemical-shift change versus protein concentration were derived from metabolite mixtures with (fatted) human and bovine albumin acting as blood-plasma mimics.

CONCLUSION

The BMS method, demonstrated on blood plasma, can also be used on other samples containing sufficient protein (> 10 g/L). Also, it allows measurement of the presence and sign of exchange-induced chemical-shift changes.

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.

Ischemia-modified albumin levels in patients with end-stage renal disease patients on hemodialysis: does albumin analysis method affect albumin-adjusted ischemia-modified albumin levels?

Ischemia-Modified albumin (IMA) has been used as an early marker in the evaluation of the patients with acute coronary syndrome. We aimed to evaluate IMA in end-stage renal disease (ESRD) patients on hemodialysis and the effect of albumin methods on albumin-adjusted IMA levels. A total of 30 ESRD patients were included in this study. Serum IMA and albumin levels were measured before and after a hemodialysis session. Albumin concentrations were determined with bromocresol green and bromocresol purple methods. Postdialysis IMA and albumin-adjusted IMA levels with two different albumin methods were significantly increased compared with the predialysis levels (P<0.05). However, we did not find any difference in albumin-adjusted IMA levels in either at the beginning or at the end of the dialysis session. IMA levels increase after hemodialysis, whereas albumin method has no effect on albumin-adjusted IMA levels.

Discrepancies in Serum Albumin Measurements Vary by Dialysis Modality

BACKGROUND

Serum albumin level is an important prognostic marker in patients with chronic renal failure. However there are discrepancies in the methods of estimation of serum albumin. The objective of this study is to evaluate the magnitude of the discrepancy in the serum albumin levels as measured by Bromcresol Green (BCG) and Bromcresol Purple (BCP) dye methods in patients on hemodialysis (HD) and peritoneal dialysis (PD) and to ascertain the clinical determinants of the discrepancy (deltaSA = BCG-BCP; g/dL) in each of the modalities.

METHOD

We measured serum and plasma albumin levels by BCG and BCP methods in 19 adult HD patients and 18 adult PD patients treated in the dialysis units of the University of Colorado Health Sciences Center. Similar measurements were performed in 10 normal adult subjects. In all groups, paired blood samples were taken to estimate the albumin in both serum and plasma. Nephelometry (NM) was subsequently performed on the serum of 13 of the HD patients, 14 of the PD patients, and each of the 10 normal subjects.

RESULTS

We found that for both the dye methods serum and plasma albumin levels are almost identical in each of the three subject groups. In the normal subjects serum albumin estimated by BCP is in good agreement with NM values but BCG overestimates the albumin levels. In the PD group the discrepancy between the BCG and BCP (deltaSA) is statistically significant with the BCG averaging 0.59 +/- 0.12 g/dL more than the BCP. The BCG values are closer to those obtained by the "gold standard", NM. In the HD group the deltaSA is significantly (p < 0.001) less than in the PD group (0.34 +/- 0.11 g/dL). As for PD, BCG values are closer to NM values. Increasing age, female gender, and higher dialysis adequacy are associated with higher deltaSA in the HD but not in the PD group. Utilizing linear regression analysis we developed equations for each dialysis modality to convert albumin measurements from one method to the other.

CONCLUSION

We confirm that a discrepancy exists between the commonly used dye methods (BCG and BCP) for serum albumin estimation. This discrepancy is significantly lower in HD patients than in PD patients. Nephrologists should be aware of this discrepancy and appropriate corrections should be made during quality improvement analysis.

Lithium heparinised blood-collection tubes give falsely low albumin results with an automated bromcresol green method in haemodialysis patients

BACKGROUND

The aim of this study was to investigate the cause of markedly low albumin values determined by a bromcresol green (BCG) method in patients on haemodialysis.

METHODS

Serum and heparinised plasma from haemodialysis patients and normal controls were collected. Albumin was measured using Beckman bromcresol purple (BCP) and Roche BCG methods on the Beckman Synchron LX20.

RESULTS

The albumin in heparinised plasma determined by a BCG method was 33.3% lower than that of the BCP method in a haemodialysis patient. The albumin values determined by the BCP method were comparable to those measured by immunonephelometric analysis for this patient. Significantly lower albumin levels were also observed in lithium heparin plasma by a BCG method compared to the BCP method in both non-renal patients (31.2+/-3.8 vs. 34.1+/-4.1 g/L, p<0.001, n=30) and haemodialysis patients (28.6+/-3.5 vs. 32.8+/-3.7 g/L, p<0.001, n=30). This negative bias was directly correlated with heparin concentrations in the plasma. The BCP method did not show this dose-dependent bias.

CONCLUSIONS

Lithium heparin plasma can cause falsely low albumin values by an automated BCG method and the suitability of lithium heparin blood tubes should be carefully assessed for haemodialysis patients. The BCP method is free of this bias.

A formula to predict corrected calcium in haemodialysis patients

BACKGROUND

The conventional calcium correction formula (corrected total calcium (mmol/L) = TCa (mmol/L) + 0.02 [40 (g/L) - albumin (g/L)]) is broadly applied for the estimation of serum calcium in haemodialysis (HD) patients, despite the fact that it was not derived or validated in a HD population. A novel formula was derived and validated for corrected serum calcium in HD patients.

METHODS

Total calcium (TCa), ionized calcium (iCa(2+)), magnesium, phosphate, albumin and bicarbonate were collected from 60 HD patients to derive the formula. A validation set of 237 stable HD patients was then examined, and subjects were classified as hyper-, hypo- and normocalcaemic based on the iCa(2+). Agreement of the new formula was calculated with iCa(2+) as the gold standard, using the intraclass correlation coefficient (ICC). This was compared to the agreement between iCa(2+) and the following: uncorrected total serum calcium (TCa), the conventional correction formula, the Orrell formula and the Clase formula.

RESULTS

Using multiple linear regression the following formula was derived: corrected total calcium (mmol/L) = TCa (mmol/L) + 0.01 [30 (g/L) - albumin (g/L)]. The new formula had superior agreement compared to all of the other formulae. There was a statistically significant greater agreement between the new formula and the iCa(2+) as compared to the conventional formula (P < 0.01). However, the new formula did not significantly outperform the Orrell formula, the Clase formula or Total calcium.

CONCLUSIONS

The use of our simple new formula should enable more appropriate decision making compared to the conventional formula in the highly complex HD population.

A review of albumin binding in CKD

Hypoalbuminemia is associated with excess mortality in patients with kidney disease. Albumin is an important oxidant scavenger and an abundant carrier protein for numerous endogenous and exogenous compounds. Several specific binding sites for anionic, neutral, and cationic ligands were described. Overall, the extent of binding depends on the ligand and albumin concentration, albumin-binding affinity, and presence of competing ligands. Chronic kidney disease affects all these determinants. This may result in altered pharmacokinetics and increased risk of toxicity. Renal clearance of albumin-bound solutes mainly depends on tubular clearance. Dialytic clearance by means of conventional hemodialysis/hemofiltration and peritoneal dialysis is limited. Other epuration techniques combining hemodialysis with adsorption have been developed. However, the benefit of these techniques remains to be proved.

Comparison of calcium phosphate product values using measurement of plasma total calcium and serum ionized calcium

Calcium phosphate product (Ca x Pi) is a clinically relevant tool to estimate the cardiovascular risk of patients with renal failure. In reports, mostly total serum calcium has been used. As measurement of serum ionized calcium has some benefits and is being used increasingly, we estimated the respective levels of calcium phosphate product using both total (t-Ca x Pi) and ionized calcium (ion-Ca x Pi). Fifty-eight healthy individuals and 180 hemodialysis (HD) patients from 2 centers were studied. Diagnostic accuracies for corresponding values of the t-Ca x Pi and ion-Ca x Pi were calculated using a GraphROC program. Of HD patients, 64% had t-Ca x Pi <4.4 mmol(2)/L(2) regarded as a desirable goal, and 10% had values over 5.6 mmol(2)/L(2) associated with a high cardiovascular risk. Based on GraphROC analysis, t-Ca x Pi of 4.4 mmol(2)/L(2) corresponded to a value of 2.2 mmol(2)/L(2) of ion-Ca x Pi and, respectively, t-Ca x Pi of 5.6 mmol(2)/L(2) corresponded 2.8 mmol(2)/L(2) of ion-Ca x Pi. Owing to the good agreement between the results in the 2 centers, these values for risk levels can be used in both centers. When measurement of ionized calcium is used, Ca x Pi values of 2.2 and 2.8 mmol(2)/L(2) can be used instead of generally used values of 4.4 and 5.6 mmol(2)/L(2) with total calcium.

L-carnitine infusions may suppress serum C-reactive protein and improve nutritional status in maintenance hemodialysis patients

Scattered reports indicate that L-carnitine may suppress proinflammatory cytokines in sick individuals without renal disease and may improve protein synthesis or nitrogen balance either in patients without renal disease or in maintenance hemodialysis (MHD) or chronic peritoneal dialysis patients. We conducted an experimental study in MHD patients to evaluate the effects of L-carnitine treatment on inflammatory and protein-energy nutritional status. MHD patients were assigned to receive intravenous injections of L-carnitine 20 mg/kg (n = 48) or placebo (n = 65) thrice weekly at the end of each hemodialysis treatment for 6 months. The carnitine-treated group showed a statistically significant decrease in serum C-reactive protein and increase in serum albumin and transferrin, blood hemoglobin, and body mass index. Conversely, in the placebo-treated group, a significant decrease was reported for serum albumin, serum transferrin, and body mass index, whereas the other considered measures did not change significantly. These preliminary findings suggest that in MHD patients, L-carnitine therapy may suppress inflammation, particularly among those patients with C-reactive protein > or =3 mg/dL, and may improve protein-energy nutritional status.

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.

Protein-bound uremic retention solutes

Protein-bound uremic retention solutes are molecules with low molecular weight (MW) but should be considered middle or high MW substances. This article describes the best known substances of this group, which include p-cresol, indoxyl sulfate, hippuric acid, 3-carboxy-4-methyl-5-propyl-2-furan-propionic acid (CMPF), and homocysteine. At concentrations encountered during uremia, p-cresol inhibits phagocyte function and decreases leukocyte adhesion to cytokine-stimulated endothelial cells. CMPF has been implicated in anemia and neurologic abnormalities of uremia. CMPF could alter the metabolism of drugs of inhibiting their binding to albumin and their tubular excretion. Indoxyl sulfate administrated to uremic rats increases the rate of progression of renal failure. Hippuric acid inhibits glucose utilization in the muscle, and its serum concentration is correlated with neurologic symptoms of uremia. Homocysteine predisposes uremic patients to cardiovascular disease through impairment of endothelial and smooth muscle cell functions. The removal of protein-bound compounds by conventional hemodialysis is low. Other strategies to decrease their concentrations include increase in dialyze pore size, daily hemodialysis, peritoneal dialysis, reduction of production or acceleration of degradation, and preservation of residual renal function.

Diagnosing undernutrition

Because of its wide prevalence and its grave consequences on the health of older persons, malnutrition requires immediate attention. Physicians in general have been described as being nutritionally blind in their slowness to recognize undernutrition. A high degree of suspicion, a thorough history and physical examination, and pertinent laboratory data can identify patients at risk. When a more comprehensive assessment is needed; screening tools, dietary history, and special biochemical parameter can be used.

Conversion between bromcresol green- and bromcresol purple-measured albumin in renal disease

BACKGROUND

Albumin measured by a bromcresol purple dye-binding assay (Alb(BCP)) agrees more closely with the gold standard of immunonephelometry than does bromcresol green (Alb(BCG)) measurement. Both tests are in current clinical use. A method for converting between the two would be useful.

METHODS

We measured albumin by bromcresol green and bromcresol purple in 535 patients, 155 of whom had renal disease. We randomly divided data from the patients with renal disease into two equal-sized sets, and used one set to derive, and the remaining set to validate, a regression equation relating the two values.

RESULTS

The relationship Alb(BCG)=5.5+Alb(BCP) performed very well in both the renal patient validation set and in the data from 380 unselected in-patients and out-patients. Intraclass correlations for agreement between measured Alb(BCG) and predicted Alb(BCG) was 0.98 in both analyses.

CONCLUSIONS

The ability to convert between these measurements will be of use in clinical situations where the absolute value of the serum albumin is important, when data from laboratories using different methodologies must be combined, and in the application of the Modification of Diet in Renal Disease formula to estimate glomerular filtration rate in patients whose albumin has been measured by bromcresol purple.

Albumin-corrected calcium and ionized calcium in stable haemodialysis patients

BACKGROUND

It is ionized calcium that is physiologically active and under homeostatic control; however, total calcium is more conveniently measured. Formulae for correction of calcium to account for albumin binding have not been validated in a dialysis setting.

METHODS

We measured ionized calcium simultaneously with total calcium (t[Ca]), albumin, total protein and pH before dialysis in 50 stable outpatients and convalescent inpatients.

RESULTS

Although 92% of patients were taking calcium supplements and 70% taking alphacalcidol, 11 patients (22%) had ionized hypocalcaemia. To facilitate comparison of calculated ionized calcium, measured total calcium (t[Ca]), and 'corrected' calcium (c[Ca]), with the criterion measure of ionized calcium, all measurements were converted to z scores, standardized on the normal range for each variable. Results are expressed as intraclass correlation coefficients (ICC: 0, all differences are due to error; 1, all differences are due to between patient variation).

CONCLUSIONS

None of the published formulae greatly improved the test characteristics beyond simply using the total calcium. A correction formula in widespread use (Payne), quoted in reference texts, agreed less well with ionized calcium than did the unadjusted measured calcium. Correction formulae should be abandoned in favour of the use of uncorrected calcium. In cases of doubt, ionized calcium should be directly measured.

Albumin as an outcome measure in haemodialysis in patients: the effect of variation in assay method

BACKGROUND

Serum/plasma albumin is an important predictor of future mortality/morbidity in haemodialysis (HD) patients and has been proposed as an important audit measure. Different methods of albumin assay give different results and the bias between methods may be greater in renal failure patients.

METHODS

Albumin concentration in plasma was measured by three methods, two dye-binding methods (bromocresol green (BCG) and bromocresol purple (BCP)) and an immuno-turbidimetric (ITM) method, in 143 HD patients (group I) and 49 non-renal patients (group II). Comparisons were made between means, variation in differences across a range of albumin concentrations and on the percentage of patients within the normal range.

RESULTS

In HD patients (group I), BCG over-estimated plasma albumin compared with the other two methods. The difference could be as much as 10 g/l and was more marked in hypoalbuminaemic patients. The BCP method gave results closer to the ITM method, particularly in HD patients. These differences were less marked in group II patients but both methods overestimated albumin compared with the ITM method. Using the BCG local laboratory normal range, 84% of HD patients had plasma albumin concentrations within the normal range but this fell to 57% if the BCP results were used.

CONCLUSIONS

The method for determining albumin concentration has a marked effect on the results particularly in HD patients. BCG, the most commonly used method, gives higher results than other methods and correlates poorly with an immunological method. These differences make comparative audit between nephrology units difficult and have implications for other biochemical variables and other specialties.

Assessment of protein energy malnutrition in older persons, Part II: Laboratory evaluation

A large proportion of chronic diseases affecting older persons can be either prevented or significantly improved by improving nutrition. This places an increased burden on health care professionals caring for older persons. Screening for malnutrition at an early stage allows the intervention to be most successful. History, physical examination, and anthropometric measurements are essential parts of any nutritional evaluation. However, these tools can be highly subjective and rely heavily on the knowledge and experience of the evaluator. Incorporating biochemical measurements in the routine nutritional assessment provides an often-needed objective dimension. Interpreting these measurements must take into consideration the normal biological changes seen with aging. In this article, we review many of the biochemical parameters used in nutritional assessment and their relation to morbidity and mortality, with a special focus on normal changes seen with aging.

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

Although the bromcresol purple (BCP) method provides high specificity in measurements of serum albumin concentrations, we discovered a reaction difference between the values for human mercaptalbumin (HMA) and human nonmercaptalbumin (HNA) measured by the BCP. We found that the color intensity of HMA with BCP present in the reduced form in the albumin of fresh serum, was lower than for HNA. While maintaining specificity for albumin, we reduced the reaction difference between HMA and HNA, with the addition of sodium dodecylsulfate and 5,5'-dithiobis(2-nitrobenzoic acid) to the BCP reagent. The mean albumin concentration by the BCP procedure for 63 fresh sera and the 63 sera stored for 2 days at room temperature were 35.6 g/L and 38.1 g/L, respectively. Those by the modified BCP procedure were 39.8 g/L and 39.9 g/L, respectively. The difference in measured values between the fresh and stored sera which is believed to be caused by the conversion of HMA to HNA during the storage of sera was not observed in the case of the modified BCP procedure. Our modified BCP method is effective in eliminating uncertainty of the albumin concentration assigned to assay calibrators for the conventional BCP method.

Association of serum albumin and mortality risk

Reduced levels of serum albumin concentration, a routine blood test, within the "normal" range have been reported to be associated with mortality risk. The literature is reviewed, with a focus on cohort studies meeting specified criteria, and findings are summarized. In studies of many populations, comprising healthy subjects and patients with acute or chronic illness, serum albumin concentration is inversely related to mortality risk in a graded manner over its entire range; the estimated increase in the odds of death ranges from 24% to 56% for each 2.5 g/l decrement in serum albumin concentration. The association predicts overall and cause-specific mortality including cardiovascular mortality. It is likely that albumin concentration is a highly sensitive indicator of preclinical disease and disease severity. A direct protective effect of the albumin molecule is suggested by the persistence of the association after adjustment for other known risk factors and preexisting illness, and after exclusion of early mortality. Although biologically plausible, there is no direct evidence for this hypothesis. Serum albumin concentration is an independent predictor of mortality risk and could be useful in the quantification of risk in a broad range of clinical and research settings.

Serum and urine albumin: a progress report on their measurement and clinical significance

For about 25 years, bromcresol green and bromcresol purple have been the basis for most of the measurements of serum albumin in the US and perhaps in the world. The longevity of the methods is due to their being simple, sensitive, specific, inexpensive and relatively free from interferences. The lack of change in the serum albumin methodology is balanced by two important developments. First, the recognition of the importance of serum albumin in the maintenance of good health, and the association of decreased concentrations with increased risk of morbidity and mortality. Second, the association of albuminuria with diabetic nephropathy, which without medical intervention could lead to end-stage renal disease. The development of accurate and precise methods for urinary albumin has provided a tool to physicians to extend the length and improve the quality of life of many diabetic individuals.

Comparison of methods for measuring albumin in peritoneal dialysis and hemodialysis patients

Serum albumin levels have been used extensively as an indicator of morbidity in patients with end-stage renal disease. Recent evidence suggests that albumin levels vary considerably in hemodialysis patients depending on the laboratory method used, but formulas for comparing albumin values by different methods have not been developed. We prospectively evaluated the effects of measuring albumin by three different methods on paired plasma and serum from 23 patients on continuous ambulatory peritoneal dialysis (CAPD) and 53 patients on chronic maintenance hemodialysis. Plasma and serum gave virtually identical results independent of method used. In CAPD patients, bromcresol green and nephelometry gave nearly identical albumin measurements through the entire range of plasma levels. In contrast, bromcresol purple gave values that were 9.9 percent +/- 1.3 percent lower (P < 0.05). Hemodialysis patients showed a similar pattern with close agreement between bromcresol green and nephelometry, but bromcresol purple gave lower albumin levels by 19.1 percent +/- 1.2 percent (P < 0.05). The discrepancy in albumin in CAPD patients was significantly less than in the hemodialysis patients (P < 0.05), suggesting that there were fewer interfering substances in the blood of CAPD patients than in hemodialysis patients. Linear regression analysis was used to develop simple formulas for comparing albumin values obtained by the different methods in CAPD and hemodialysis patients. These studies show that values for albumin in blood vary significantly by method of analysis in CAPD and hemodialysis patients. By the use of these formulas, it becomes possible to compare albumin values between centers using different methods for the purpose of quality management.

Serum albumin concentration-related Health Care Financing Administration quality assurance criterion is method-dependent: revision is necessary

The objective of this study was to examine quantitative differences between the two commonly used methods for determining serum albumin concentration, bromcresol green (BCG) and bromcresol purple (BCP), in normal subjects and in 235 unselected dialysis patients in view of recently established Health Care Financing Administration (HCFA) quality assurance review criteria. The mean of normal results by the BCG method was 4.4 g/dL, and 97.5% of values were 3.8 g/dL or higher. The mean of normal results by the BCP method was 3.9 g/dL, and 97.5% of values were 3.3 g/dL or higher. Serum albumin concentrations in samples from the dialysis patients had respectively lower mean values by both methods. For the BCG method, the mean was 3.8 g/dL, and 82% of values were 3.5 g/dL or higher; for the BCP method, the mean was 3.3 g/dL, and 82% of values were 3.0 g/dL or higher. Likewise, for the reference immunonephelometric procedure, the mean value for the dialysis patients was 3.3 g/dL, and 82% of values were 3.0 g/dL or higher. For the samples from the dialysis patients, in comparison with the immunonephelometric method, the BCG method exhibited both constant (intercept = 9.3 g/L) and proportional error (slope = 0.87). The mean albumin value for the BCG method was 3.8 g/dL, 15% higher. In contrast, the BCP method compared closely with the reference method: slope = 1.00, intercept = 0.8 g/L, mean x = 3.3 g/dL, mean y = 3.3 g/dL. The HCFA quality assurance criteria are valid only for the BCG method.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of renal transplantation on a major endogenous ligand retained in uremic serum

The effects of renal transplantation on serum concentrations of 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and indole-3-acetic acid (IAA), which are endogenous ligands retained in uremic serum, and on phenytoin binding to serum protein were investigated. IAA, a weakly bound ligand, was rapidly excreted by the transplanted kidney during the first one to three days after renal transplantation, but CMPF, a strongly bound ligand, was slowly excreted. The binding defect of phenytoin was partially corrected by transplantation during the period of study. The results suggested that the prolonged drug binding defect observed despite successful renal transplantation is caused by a slower decrease of strongly bound ligands such as CMPF retained in uremic serum; hypoalbuminemia, usually observed after transplantation, may also contribute to this phenomenon.