A comparison of the measurement of sodium and potassium by flame photometry and ion-selective electrode

Single flow-based system for the automatic multiparametric nutrients (NPK & Fe) assessment in soil leachates

A multiparametric sequential injection system for the determination of phosphate, nitrite, nitrate, potassium, and iron(III) in a single manifold was developed. The main goal of the proposed method was to develop an efficient tool to assess a number of essential chemical compounds in soils, providing the corresponding information on soil fertility and, additionally, information on possible groundwater contamination. The method was applied for the quantification of the aforementioned parameters in simulated leachates produced in laboratory-scale core columns. The relative standard deviations of ten replicate analyses of a standard were: 6% for phosphate; 2% for nitrite; 2% for nitrate; 5% for potassium; and 6% for iron(III). The limits of detection and quantification were: 2.15 and 7.18 μmol/L for phosphate determination; 0.22 and 0.73 μmol/L for nitrite determination; 3.42 and 8.00 μmol/L for nitrate determination; 39 μmol/L (limit of detection) for potassium determination; and 0.46 and 1.85 μmol/L for iron(III) determination. The sequential injection system was successfully applied for the quantification of multiple soil chemical components (PO43-, NO2-, NO3-, K+, and Fe3+) in soil leachates. The analysis of a sample, involving all the analytes, has a duration of 28 min.

Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management

Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample's water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Use of the osmolal gap in diagnosing mixed physiology hyponatremia in a child with B-cell acute lymphoblastic leukemia

Hyponatremia is common among children undergoing treatment for hematologic malignancies and may be attributed to multiple underlying causes. In cases of hyponatremia due to mixed physiology, the osmolal gap, can identify pseudohyponatremia that may be masked by other causes.

Mapping the forage nitrogen, phosphorus, and potassium contents of alpine grasslands by integrating Sentinel-2 and Tiangong-2 data

Nitrogen (N), phosphorus (P), and potassium (K) contents are crucial quality indicators for forage in alpine natural grasslands and are closely related to plant growth and reproduction. One of the greatest challenges for the sustainable utilization of grassland resources and the development of high-quality animal husbandry is to efficiently and accurately obtain information about the distribution and dynamic changes in N, P, and K contents in alpine grasslands. A new generation of multispectral sensors, the Sentinel-2 multispectral instrument (MSI) and Tiangong-2 moderate-resolution wide-wavelength imager (MWI), is equipped with several spectral bands suitable for specific applications, showing great potential for mapping forage nutrients at the regional scale. This study aims to achieve high-accuracy spatial mapping of the N, P, and K contents in alpine grasslands at the regional scale on the eastern Qinghai-Tibet Plateau. The Sentinel-2 MSI and Tiangong-2 MWI data, coupled with multiple feature selection algorithms and machine learning models, are applied to develop forage N, P, and K estimation models from data collected at 92 sample sites ranging from the vigorous growth stage to the senescent stage. The results show that the spectral bands of both the Sentinel-2 MSI and Tiangong-2 MWI have an excellent performance in estimating the forage N, P, and K contents (the R² values are 0.68-0.76, 0.54-0.73, and 0.74-0.82 for forage N, P, and K estimations, respectively). Moreover, the model integrating the spectral bands of these two sensors explains 78%, 74%, and 84% of the variations in the forage N, P, and K contents, respectively. These results indicate that the estimation ability of forage nutrients can be further improved by integrating Tiangong-2 MWI and Sentinel-2 MSI data. In conclusion, integration of the spectral bands of multiple sensors is a promising approach to map the forage N, P, and K contents in alpine grasslands with high accuracy at the regional scale. This study offers valuable information for growth monitoring and real-time determination of forage quality in alpine grasslands.

Quantifying the effects of co-composting organic biomass mixtures with inorganic amendments to obtain value-added bio-products

Co-digestion of organic biomass mixed with inorganic amendments could have an impact on composting dynamics. Various studies highlighted fertilizers' role as an additive to lesser the nitrogen loss, while some studies focused on the addition of fertilizers to enhance the efficiency. The changes in carbon, nitrogen components, and humic substances during the organic-inorganic co-compost process were seldom studied. Clarifying these changes might help improve the production process and compost nutrients contents. Thus, this study's purpose is to investigate the effects of inorganic amendments on compost characteristics, compost temperature, biochemical methane production (BMP), and nutritional contents. The inorganic phosphorous (P), sulfur (S), and sulfur solubilizing agent (SSA) were added to Farmyard manure (FYM) mixed with biodegradable waste (BW), including wheat straw, corn stalks, and green lawn waste. The P and S amended treatments were carried out into two sets, with and without SSA. The mixed feedstocks were added in the insulated RBC composting pit (15 x 15 x 10 feet). The compost material's moisture content was maintained 50-65% during the entire composting process for optimum waste digestion i.e., the moisture content (MC) of FYM was 82.7% and for BW ranged 8.8-10.2%, while the C/N ratio was found 10.5 for FYM, 74.5 for wheat straw, 83.5 for corn stalks, and 84.8 for lawn waste. At the condition of compost maturity, the inorganic amendments have no significant effect on composted material's moisture content. The maximum organic matter of 69.7% and C/N ratio of 44.6 was measured in T1. On the 6th day of composting, the temperature reached to thermophilic range (>45 oC) in all the treatments due to aeration of compost increased microbial activities and waste decomposition rate and decreased gradually to mesophilic range (35-45 oC) because the supply of high-energy compounds becomes exhausted. The highest temperature was reached in T4 (58 oC) and lowest in CT (47 oC). The significantly maximum methane of 8.95 m3 and biogas burning was 818 minutes in CT, followed by T1 and T4. The results of this study revealed that P enriched compost is a feasible and sustainable way to overcome P deficiency in the soil as well as in plants and best way to use low-grade P and organic waste material.

Metagenomic discovery and functional validation of L-asparaginases with anti-leukemic effect from the Caspian Sea

By screening 27,000 publicly available prokaryotic genomes, we recovered ca. 6300 type I and ca. 5200 type II putative L-asparaginase highlighting the vast potential of prokaryotes. Caspian water with similar salt composition to the human serum was targeted for in silico L-asparaginase screening. We screened ca. three million predicted genes of its assembled metagenomes that resulted in annotation of 87 putative L-asparaginase genes. The L-asparagine hydrolysis was experimentally confirmed by synthesizing and cloning three selected genes in E. coli. Catalytic parameters of the purified enzymes were determined to be among the most desirable reported values. Two recombinant enzymes represented remarkable anti-proliferative activity (IC50 <1IU/ml) against leukemia cell line Jurkat while no cytotoxic effect on human erythrocytes or human umbilical vein endothelial cells was detected. Similar salinity and ionic concentration of the Caspian water to the human serum highlights the potential of secretory L-asparaginases recovered from these metagenomes as potential treatment agents.

Combined imaging of potassium and sodium in human skeletal muscle tissue at 7 T

PURPOSE

To validate the feasibility of quantitative combined potassium (³⁹ K) and sodium (²³ Na) MRI in human calf muscle tissue, as well as to evaluate the reproducibility of the apparent tissue potassium concentration (aTPC) and apparent tissue sodium concentration (aTSC) determination in healthy muscle tissue.

METHODS

Quantitative ²³ Na and ³⁹ K MRI acquisition protocols were implemented on a 7 T MR system. A double-resonant ²³ Na/³⁹ K birdcage RF coil was used. Measurements of human lower leg were performed in a total acquisition time of TA_Na = 10:54 min/TA_K = 8:06 min and using a nominal spatial resolution of 2.5 × 2.5 × 15 mm³ /7.5 × 7.5 × 30 mm³ for ²³ Na/³⁹ K MRI. Two aTSC and aTPC examinations in muscle tissue were performed during the same day on 10 healthy subjects.

RESULTS

The proposed acquisition and postprocessing workflow for ²³ Na and ³⁹ K MRI data sets provided reproducible aTSC and aTPC measurements. In human calf muscle tissue, the coefficient of variation between scan and re-scan was 5.7% for both aTSC and aTPC determination. Overall, mean values of aTSC = (17 ± 1) mM and aTPC = (85 ± 5) mM were measured. Moreover, for ³⁹ K in calf muscle tissue, T 2 ∗ components of T 2 f ∗ = (1.2 ± 0.2) ms and T 2 s ∗ = (7.9 ± 0.9) ms, as well as a residual quadrupolar interaction of ω q ¯ = (143 ± 17) Hz, were determined. The fraction of the fast component was f = (58 ± 4)%.

CONCLUSION

Using the presented measurement and postprocessing approach, a reproducible aTSC and aTPC determination using ²³ Na and ³⁹ K MRI at 7 T in human skeletal muscle tissue is feasible in clinically acceptable acquisition durations.

Formulae to correct sodium concentrations for serum water fraction in cases of hypo- and hyperproteinemia in cats

BACKGROUND

Biochemistry analyzers in many high-throughput laboratories use indirect potentiometry to determine serum electrolyte concentrations, which involves a pre-analytical dilution step that may be associated with artifactual increases or decreases in electrolyte concentrations under circumstances of altered serum water fraction (SWF). Severe hypo- and hyperproteinemia, conditions that cause altered SWF, are recognized but under-emphasized causes of falsely measured serum sodium concentrations.

OBJECTIVES

The goals of this study were to determine the average actual SWF (SWF_A ) and establish formulae to correct serum sodium concentration measured by indirect potentiometry in hypo- and hyperproteinemic cats.

METHODS

Serum samples from 112 feline patients were analyzed for electrolytes (measured by both indirect and direct potentiometry), total protein, albumin, triglycerides, and cholesterol. Each serum sample was also lyophilized to determine the SWF_A . A feline-specific formula to estimate SWF (SWF_E-FEL ) was developed and evaluated with a multivariable linear model.

RESULTS

The mean SWF_A in this population of cats was 91.2%, which was significantly different (P < .0001) than the mean (93.9%) calculated using the human estimated formula (SWF_E-HUM ). The formula devised for the SWF_E-FEL better recapitulated the SWF_A than did the SWF_E-HUM , and the corrected sodium concentrations calculated using the feline formula were better correlated with serum sodium measured by direct potentiometry than those determined using the human formula.

CONCLUSIONS

Application of feline-specific formulae is expected to limit the misinterpretation of electrolyte data from indirect potentiometry when altered SWF occurs. To demonstrate this, a case example of a hypoproteinemic cat is provided.

Fluid and Electrolyte Transport across the Peritoneal Membrane during CAPD According to the Three-pore Model

In the present review, we summarize the principles governing the transport of fluid and electrolytes across the peritoneum during continuous ambulatory peritoneal dialysis (CAPD) in “average” patients and during ultrafiltration failure (UFF), according to the three-pore model of peritoneal transport. The UF volume curves as a function of dwell time [V( t)] are determined in their early phase by the glucose osmotic conductance [product of the UF coefficient (LpS) and the glucose reflection coefficient (σg)] of the peritoneum; in their middle portion by intraperitoneal volume and glucose diffusivity; and in their late portion by the LpS, Starling forces, and lymph flow. The most common cause of UFF is increased transport of small solutes (glucose) across the peritoneum, whereas the LpS is only moderately affected. Concerning peritoneal ion transport, ions that are already more or less fully equilibrated across the membrane at the start of the dwell, such as Na+(Cl–), Ca2+, and Mg2+, have a convection-dominated transport. The removal of these ions is proportional to UF volume (approximately 10 mmol/L Na+and 0.12 mmol/L Ca2+removed per deciliter UF in 4 hours).

The present article examines the impact on fluid and solute transport of varying concentrations of Ca2+and Na+in peritoneal dialysis solutions. Particularly, the effect of “ultralow” sodium solutions on transport and UF is simulated and discussed. Ions with high initial concentration gradients across the peritoneum, such as K+, phosphate, and bicarbonate, display a diffusion-dominated transport. The transport of these ions can be adequately described by non-electrolyte equations. However, for ions that are in (or near) their diffusion equilibrium over the peritoneum (Na+, Ca2+, Mg2+), more complex ion transport equations need to be used. Due to the complexity of these equations, however, non-electrolyte transport formalism is commonly employed, which leads to a marked underestimation of mass transfer area coefficients (PS). This can be avoided by determining the PS when transperitoneal ion concentration gradients are steep.

Vecuronium- and Esmolol-Induced Pseudohypernatremia Due to Drug Interference With Ion-Selective Electrodes

Objectives

We observed that patients treated with continuous vecuronium or esmolol infusions showed elevated plasma sodium measurements when measured by the routine chemistry analyzer as part of the basic metabolic panel (Vitros 5600; Ortho Clinical Diagnostics, Raritan, NJ), but not by blood gas analyzers (RAPIDLab 1265; Siemens, Tarrytown, NY). Both instruments use direct ion-selective electrode technology, albeit with different sodium ionophores (basic metabolic panel: methyl monensin, blood gas: glass). We questioned if the basic metabolic panel hypernatremia represents artefactual pseudohypernatremia.

Design

We added vecuronium bromide or esmolol hydrochloric acid to pooled plasma samples and compared sodium values measured by both methodologies. We queried sodium results from the electronic medical records of patients admitted at Children's Hospital of Philadelphia from 2016 to 2018 and received vecuronium and/or esmolol infusion treatment during their admissions.

Setting

PICU of a quaternary, free-standing children's hospital.

Patients

Children admitted to the hospital who received vecuronium and/or esmolol infusion.

Measurements and Main Results

Sodium was measured in pooled plasma samples by basic metabolic panel and blood gas methodologies after adding vecuronium bromide or esmolol hydrochloric acid, leading to a dose-response increase in basic metabolic panel sodium measurements. A repeated measures regression analysis of our electronic medical records showed that the vecuronium dose predicted the Δ sodium (basic metabolic panel-blood gas) sodium within 12 hours of the vecuronium administration (p < 0.0018). Esmolol showed a similar trend (p = 0.13). This occurred primarily in central line samples with continuous vecuronium or esmolol infusions.

Conclusions

Vecuronium and esmolol can falsely elevate direct ion-selective electrode sodium measurements on Vitros chemistry analyzers. Unexpectedly high sodium measurements in patients receiving vecuronium and/or esmolol infusions should be further investigated with an alternate sample type (i.e., peripheral blood) or measurement methodology (i.e., blood gas) to guide treatment decisions.

Negative Dialysate to Sodium Gradient Does not Lead to Intracellular Volume Expansion Post Hemodialysis

Introduction

Intradialytic hypotension remains the most common complication of routine outpatient hemodialysis treatments. There is debate as to the optimum dialysate sodium concentration, with hypotonic dialysates potentially causing intracellular swelling and hypertonic ones intracellular dehydration.

Methods

Multi-frequency bioimpedance was used to assess extracellular and intracellular fluid volumes in 53 adult hemodialysis patients. Dialysate sodium was checked by ion electrophoresis.

Results

The mean decrease in extracellular volume and intracellular volumes were 1.01 ±0.09 and 0.88 ±0.18 kg, respectively. The median dialysate to sodium gradient was −3 mmol/L (−1 to −6), with a median dialysate sodium of 136 mmol/L (136–138). There was no association between changes in body fluid composition and sodium concentrations, or gradients. The mean difference between dialysate sodium prescribed and delivered was 2.4 ±0.8 mmol/L.

Conclusions

In this study we were unable to demonstrate a relationship between predialysis serum sodium and the dialysate sodium prescribed and changes in extracellular or intracellular fluid volumes. However this study showed that using a negative sodium gradient, patients can be successfully ultrafiltrated without setting up intracompartmental fluid gradients. The caveat is that the prescribed dialysate to serum sodium gradient may differ from the actual gradient.

Effects of 17β-estradiol on cardiac Na(+)/K(+)-ATPase in high fat diet fed rats

The aim of this study was to investigate in vivo effects of estradiol on Na(+)/K(+)-ATPase activity/expression in high fat (HF) diet fed rats. Adult male Wistar rats were fed normally (Control, n = 7) or with a HF diet (Obese, n = 14) for 10 weeks. After 10 weeks, half of the obese rats were treated with estradiol (Obese + Estradiol, n = 7, 40 μg/kg, i.p.) as a bolus injection and 24 h after treatment all the rats were sacrificed. Estradiol in vivo in obese rats in comparison with obese non-treated rats led to a statistically significant increase in concentration of serum Na(+) (p < 0.05), Na(+)/K(+)-ATPase activity (p < 0.01), expression of α1 (p < 0.01) and α2 (p < 0.05) subunit of Na(+)/K(+)-ATPase, both PI3K subunits p85 (p < 0.01), p110 (p < 0.05), and association of IRS-1 with p85 (p < 0.05), while significantly decrease expression of AT1 (p < 0.05) and Rho A (p < 0.01) proteins. Our results suggest that estradiol in vivo in pathophysiological conditions, such as obesity accompanied with insulin resistance stimulates activity and expression of Na(+)/K(+)-ATPase by a mechanism that involves the participation of IRS-1/PI3K/Akt signaling. In addition, the decreasing level of AT1 and Rho A proteins estradiol probably attenuates the detrimental effect of obesity to decreased IRS-1/PI3K association and consequently reduce Na(+)/K(+)-ATPase activity/expression.

Synthesis of thiol derivatives of azobenzocrown ethers. The preliminary studies on recognition of alkali metal ions by gold nanoparticles functionalized with azobenzocrown and lipoic acid

The article presents the synthesis of novel 13- and 16-membered azobenzocrown derivatives with peripheral thiol moieties and preliminary studies assessing their possible application in plasmonic sensors based on gold nanoparticles. The effect of the length of the chain connecting the macrocycle with the thiol group and the effect of the presence of the additional functional compound, i.e. lipoic acid, on the sensor response was analyzed. Colloidal gold nanoparticles modified with a 16-membered crown with a thiol group on oxyethylene (compound 12) or oxybutylene (compound 13) linker was found to have good properties, allowing for detection of potassium ions in aqueous solutions at concentrations 8-20 mM for bifunctionalized nanogold and 4-26 mM for less stable, colloidal gold modified only with thiol derivatives of azobenzocrowns. The response towards potassium cations of bifunctionalized nanogold modified with compound 13 was more stable in time than for the system incorporating compound 12. Compound 13, obtained with the highest yield among all presented thiol derivatives of azobenzocrowns, was selected for further, more detailed, studies.

Associations between serum potassium and sodium levels and risk of hypertension: a community-based cohort study

Objective

Several studies have examined the relationships between dietary potassium and sodium and hypertension, but few have evaluated the association between serum potassium or sodium and risk of incident hypertension. We therefore investigated the associations between serum potassium and sodium and risk of incident hypertension in a Chinese community-based population.

Methods

A total of 839 normotensive individuals without cardiovascular disease from the Chinese Multi-Provincial Cohort Study who took part in the baseline examination in 2007–2008 and the follow-up survey in 2012–2013 were included in this study. Odds ratios (OR) and 95% confidence intervals (95%CI) for baseline serum potassium and sodium in relation to the risk of new-onset hypertension were evaluated using multivariate logistic regression models.

Results

During five years of follow-up, 218 (26.0%) individuals progressed to hypertension. Logistic regression adjusting for multiple confounders showed that every 1 mEq/L increment in baseline serum potassium level was associated with a 75% increased risk of hypertension (OR: 1.75; 95%CI: 1.01–3.04; P = 0.04). Compared with adults with serum potassium level of 4.20–4.79 mEq/L, adults with level ≥ 4.80 mEq/L had an 84% increased risk of hypertension (OR: 1.84; 95%CI: 1.14–2.96; P = 0.01). There was no significant association between serum sodium and risk of hypertension (OR: 0.96; 95%CI: 0.89–1.04; P = 0.33).

Conclusions

Baseline serum potassium level, but not baseline serum sodium level, was positively related to the risk of incident hypertension in the Chinese population.

In vivo effects of 17β-estradiol on cardiac Na(+)/K(+)-ATPase expression and activity in rat heart

In this study the in vivo effects of estradiol in regulating Na(+)/K(+)-ATPase function in rat heart was studied. Adult male Wistar rats were treated with estradiol (40μg/kg, i.p.) and after 24h the animals were sacrificed and the heart excised. Following estradiol administration, cardiac Na(+)/K(+)-ATPase activity, expression of the α1 subunit, and phosphorylation of the α1 subunit were significantly increased. These animals also had significantly decreased levels of digoxin-like immunoreactive factor(s). Na(+) levels were also significantly reduced but to a level that was still within the normal physiological range, highlighting the ability of the Na(+)/K(+)-ATPase to balance the ionic composition following treatment with estradiol. Estradiol treated rats also showed increased phosphorylation of protein kinase B (Akt), and extracellular-signal-regulated kinase 1/2 (ERK1/2). We therefore suggest a role for Akt and/or ERK1/2 in estradiol-mediated regulation of cardiac Na(+)/K(+)-ATPase expression and activity in rat heart.

Sodium concentration measurement during hemodialysis through ion-exchange resin and conductivity measure approach: in vitro experiments

Sodium measurement during hemodialysis treatment is important to preserve the patient from clinical events related to hypo- or hyper-natremia Usually, sodium measurement is performed through laboratory equipment which is typically expensive, and requires manual intervention. We propose a new method, based on conductivity measurement after treatment of dialysate solution through ion-exchange resin. To test this method, we performed in vitro experiments. We prepared 40 ml sodium chloride (NaCl) samples at 280, 140, 70, 35, 17.5, 8.75, 4.375 mEq/l, and some “mixed samples”, i.e., with added potassium chloride (KCl) at different concentrations (4.375-17.5 mEq/l), to simulate the confounding factors in a conductivity-based sodium measurement. We measured the conductivity of all samples. Afterwards, each sample was treated for 1 min with 1 g of Dowex G-26 resin, and conductivity was measured again. On average, the difference in the conductivity between mixed samples and corresponding pure NaCl samples (at the same NaCl concentration) was 20.9%. After treatment with the exchange resin, it was 14.7%, i.e., 42% lower. Similar experiments were performed with calcium chloride and magnesium chloride as confounding factors, with similar results. We also performed some experiments on actual dialysate solution during hemodialysis sessions in 15 patients, and found that the correlation between conductivity measures and sodium concentration improved after resin treatment (R=0.839 before treatment, R=0.924 after treatment, P<0.0001). We conclude that ion-exchange resin treatment coupled with conductivity measures may improve the measurement of sodium compared to conductivity measures alone, and may become a possible simple approach for continuous and automatic sodium measurement during hemodialysis.

Low serum magnesium and the development of atrial fibrillation in the community: the Framingham Heart Study

BACKGROUND

Low serum magnesium has been linked to increased risk of atrial fibrillation (AF) after cardiac surgery. It is unknown whether hypomagnesemia predisposes to AF in the community.

METHODS AND RESULTS

We studied 3530 participants (mean age, 44 years; 52% women) from the Framingham Offspring Study who attended a routine examination and were free of AF and cardiovascular disease. We used Cox proportional hazard regression analysis to examine the association between serum magnesium at baseline and risk of incident AF. Analyses were adjusted for conventional AF risk factors, use of antihypertensive medications, and serum potassium. During up to 20 years of follow-up, 228 participants developed AF. Mean serum magnesium was 1.88 mg/dL. The age- and sex-adjusted incidence rate of AF was 9.4 per 1000 person-years (95% confidence interval, 6.7-11.9) in the lowest quartile of serum magnesium (≤1.77 mg/dL) compared with 6.3 per 1000 person-years (95% confidence interval, 4.1-8.4) in the highest quartile (≥1.99 mg/dL). In multivariable-adjusted models, individuals in the lowest quartile of serum magnesium were ~50% more likely to develop AF (adjusted hazard ratio, 1.52; 95% confidence interval, 1.00-2.31; P=0.05) compared with those in the upper quartiles. Results were similar after the exclusion of individuals on diuretics.

CONCLUSIONS

Low serum magnesium is moderately associated with the development of AF in individuals without cardiovascular disease. Because hypomagnesemia is common in the general population, a link with AF may have potential clinical implications. Further studies are warranted to confirm our findings and to elucidate the underlying mechanisms.

Agreement of two different laboratory methods used to measure electrolytes

Aim:

The aim of our study was to do an agreement analysis of two different laboratory methods used to measure electrolytes i.e., between the ISE based Beckman Coulter Synchron CX9 PRO Biochemistry analyzer and RAL's Ion3 Flame Photometer (Técnica para el Laboratorio, Barcelona, Spain), in serum samples.

Materials and Methods:

This cross sectional study was done over a period of three months from September’09 through December’09 on routine biochemistry samples. A total of 6492 samples were received for routine biochemistry analysis from those 630 blood samples were randomly processed for this study. Two ml of sample was taken in a plain gel tube (LABTECH Disposables, Ahmedabad, India), centrifuged and further processed using both systems within one hour of the sampling to obtain the Na and K concentrations in the samples. The bias and variability of differences in measured values were analyzed according to Bland and Altman method.

Results:

Flame photometry method has drawbacks such as low throughput, requires manual operation, is a time consuming procedure. Ion selective electrodes technique is a more universal method for the high throughput determination of electrolytes in physiological samples; Beckman Coulter Synchron CX9 PRO is an example of such a system. The mean difference between the two methods (standard minus test) and 95% limits of agreement for sodium in serum was -7.8±17.3 (-42.2 to 26.6) and in urine was -22±41 (-104 to 60). Similarly, the mean difference between the two methods for potassium values in serum was found to be -0.25±0.75 (-1.75 to 1.25) and in urine was -5.3±38.9 (-83.1 to 72.5). With 95% confidence interval, the value of sodium and potassium as determined by both the methods lie between the upper and lower limit showing 95% limits of agreement.

Conclusion:

Good degree of agreement was seen on comparing the two methods for measuring the electrolytes; the use of Synchron CX9 in place of Flame photometer for electrolyte analysis in serum and urine is justified or use the two interchangeably.

Disagreement between ion selective electrode direct and indirect sodium measurements: estimation of the problem in a tertiary referral hospital

PURPOSE

We estimated the proportion of indirect ion selective electrode (ISE) plasma sodium analyses in intensive care unit (ICU) and hospital wide, exhibiting important disagreement with direct ISE results in relation to abnormal plasma protein concentrations.

MATERIALS AND METHODS

Direct and indirect ISE plasma sodium measurements were performed on 346 clinical specimens selected to reflect low, normal, or high total protein concentrations. Important intermethod disagreement was defined as |4| mmol/L or higher. Results were extrapolated to a 3-month laboratory series of 48,033 indirect ISE assays, including 2877 samples from intensive care.

RESULTS

Intermethod sodium disagreement at |4| mmol/L or higher was predicted for 25% of ICU samples. Almost all (97%) occurred in hypoproteinemic samples where indirect tended to exceed direct ISE estimates. Hospital wide, such disagreement was projected to occur in 8% of samples, of which the majority (70%) were also hypoproteinemic.

CONCLUSIONS

Important disagreement between indirect and direct ISE sodium measurements may exist in up to 1 in 4 ICU specimens and 1 in 12 hospital-wide samples. The main problem is indirect ISE overestimation associated with hypoproteinemia, potentially leading to misclassifications of pseudohypernatremia and pseudonormonatremia. We recommend that hospital laboratories consider standardization using direct ISE sodium measurement.

Pseudohyponatremia revisited: a modern-day pitfall

Factitiously low sodium estimations are a hazard in most modern clinical laboratories. Most modern high-throughput analyzers use indirect ion-selective electrodes to estimate electrolyte concentrations in serum samples. This analysis is preceded by a dilution step of the sample. If the water concentration is altered by the presence of increased lipid or protein, the dilution step and the subsequent calculation of concentration by the analyzer results in a falsely low sodium value. This places patients at risk, particularly if the factitious result is acted upon by the physician. In this short review, we highlight this problem and review the methodology and situations where this artifact can occur and discuss strategies to circumvent this problem. When factitious results are suspected, whole blood sodium can be assessed using a direct ion-selective electrode, by measurement of osmolality, or by calculation of the serum water fraction and applying a correction to the reported value.

Lack of association between serum magnesium and the risks of hypertension and cardiovascular disease

BACKGROUND

Experimental studies have linked hypomagnesemia with the development of vascular dysfunction, hypertension, and atherosclerosis. Prior clinical studies have yielded conflicting results but were limited by the use of self-reported magnesium intake or short follow-up periods.

METHODS

We examined the relationship between serum magnesium concentration and incident hypertension, cardiovascular disease (CVD), and mortality in 3,531 middle-aged adult participants in the Framingham Heart Study offspring cohort. Analyses were performed using Cox proportional hazards regressions, adjusted for traditional CVD risk factors.

RESULTS

Follow-up was 8 years for new-onset hypertension (551 events) and 20 years for CVD (554 events). There was no association between baseline serum magnesium and the development of hypertension (multivariable-adjusted hazards ratio per 0.15 mg/dL 1.03, 95% CI 0.92-1.15, P = .61), CVD (0.83, 95% CI 0.49-1.40, P = .49), or all-cause mortality (0.77, 95% CI 0.41-1.45, P = .42). Similar findings were observed in categorical analyses, in which serum magnesium was modeled in categories (<1.5, 1.5-2.2, >2.2 mg/dL) or in quartiles.

CONCLUSIONS

In conclusion, data from this large, community-based cohort do not support the hypothesis that low serum magnesium is a risk factor for developing hypertension or CVD.

Interindividual variation in serum sodium and longitudinal blood pressure tracking in the Framingham Heart Study

BACKGROUND

Recent cross-sectional studies have suggested that higher serum sodium levels may be a marker of elevated blood pressure. It is unclear whether serum sodium levels are related to the risk of developing hypertension in the community.

METHODS

We investigated the association of serum sodium with longitudinal blood pressure tracking and incidence of hypertension in 2172 nonhypertensive Framingham Offspring Study participants (mean age 42 years, 54% women). We defined an increase in blood pressure as an increment of at least one category (as defined by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure), and incident hypertension as a systolic blood pressure of at least 140 or a diastolic blood pressure of at least 90 mmHg, or use of antihypertensive medications. Serum sodium was analyzed as a continuous variable, and as categories.

RESULTS

Cross-sectionally, serum sodium was not associated with systolic or diastolic blood pressure (P exceeded 0.10). On follow-up (mean 4.4 years), 805 participants (37%, 418 women) progressed by at least one blood pressure category, and 318 (15%, 155 women) developed new-onset hypertension. In multivariable logistic regression analyses (adjusting for age, sex, baseline blood pressure, diabetes, BMI, weight gain and smoking), serum sodium was not associated with blood pressure progression (odds ratio per SD increment 0.93, 95% confidence interval 0.85-1.03), or with hypertension incidence (odds ratio per SD increment 0.94, 95% confidence interval 0.82-1.08).

CONCLUSION

In our large community-based sample, serum sodium was not associated with blood pressure cross-sectionally, or with blood pressure tracking or hypertension incidence longitudinally.

Ammonium toxicity and potassium limitation in yeast

DNA microarray analysis of gene expression in steady-state chemostat cultures limited for potassium revealed a surprising connection between potassium and ammonium: potassium limits growth only when ammonium is the nitrogen source. Under potassium limitation, ammonium appears to be toxic for Saccharomyces cerevisiae. This ammonium toxicity, which appears to occur by leakage of ammonium through potassium channels, is recapitulated under high-potassium conditions by over-expression of ammonium transporters. Although ammonium toxicity is well established in metazoans, it has never been reported for yeast. To characterize the response to ammonium toxicity, we examined the filtrates of these cultures for compounds whose excretion might serve to detoxify the ammonium (such as urea in mammals). Using liquid chromatography-tandem mass spectrometry to assay for a wide array of metabolites, we detected excreted amino acids. The amounts of amino acids excreted increased in relation to the severity of growth impairment by ammonium, suggesting that amino acid excretion is used by yeast for ammonium detoxification.

Clinical review: the meaning of acid-base abnormalities in the intensive care unit part I - epidemiology

Acid-base abnormalities are common in critically ill patients. Our ability to describe acid-base disorders must be precise. Small differences in corrections for anion gap, different types of analytical processes, and the basic approach used to diagnose acid-base aberrations can lead to markedly different interpretations and treatment strategies for the same disorder. By applying a quantitive acid-base approach, clinicians are able to account for small changes in ion distribution that may have gone unrecognized with traditional techniques of acid-base analysis. Outcome prediction based on the quantitative approach remains controversial. This is in part due to use of various technologies to measure acid-base variables, administration of fluid or medication that can alter acid-base results, and lack of standardized nomenclature. Without controlling for these factors it is difficult to appreciate the full effect that acid-base disorders have on patient outcomes, ultimately making results of outcome studies hard to compare.

Unmeasured anions in critically ill patients: can they predict mortality?

OBJECTIVE

To determine whether base excess, base excess caused by unmeasured anions, and anion gap can predict lactate in adult critically ill patients, and also to determine whether acid-base variables can predict mortality in these patients.

DESIGN

Retrospective study.

SETTING

Adult intensive care unit of tertiary hospital.

PATIENTS

Three hundred adult critically ill patients admitted to the intensive care unit.

INTERVENTIONS

Retrieval of admission biochemical data from computerized records, quantitative biophysical analysis of data with the Stewart-Figge methodology, and statistical analysis.

MEASUREMENTS AND MAIN RESULTS

We measured plasma Na+, K+, Mg2+, Cl-, HCO3-, phosphate, ionized Ca2+, albumin, lactate, and arterial pH and Paco2. All three variables (base excess, base excess caused by unmeasured anions, anion gap) were significantly correlated with lactate (r2 =.21, p <.0001; r2 =.30, p <.0001; and r2 =.31. p <.0001, respectively). Logistic regression analysis showed that the area under the receiver operating characteristic (AUROC) curves had moderate to high accuracy for the prediction of a lactate concentration >5 mmol/L: AUROC curves, 0.86 (95% confidence interval [CI], 0.78-0.94), 0.86 (95% CI, 0.78-0.93), and 0.85 (95% CI, 0.77-0.92), respectively. Logistic regression analysis showed that hospital mortality rate correlated significantly with Acute Physiology and Chronic Health Evaluation (APACHE) II score, anion gap corrected (anion gap corrected by albumin), age, lactate, anion gap, chloride, base excess caused by unmeasured anions, strong ion gap, sodium, bicarbonate, strong ion difference effective, and base excess. However, except for APACHE II score, AUROC curves for mortality prediction were relatively small: 0.78 (95% CI, 0.72-0.84) for APACHE II, 0.66 (95% CI, 0.59-0.73) for lactate, 0.64 (95% CI, 0.57-0.71) for base excess caused by unmeasured anions, and 0.63 (95% CI, 0.56-0.70) for strong ion gap.

CONCLUSIONS

Base excess, base excess caused by unmeasured anions, and anion gap are good predictors of hyperlactatemia (>5 mmol/L). Acid-base variables and, specifically, "unmeasured anions" (anion gap, anion gap corrected, base excess caused by unmeasured anions, strong ion gap), irrespective of the methods used to calculate them, are not accurate predictors of hospital mortality rate in critically ill patients.

Serum potassium is not associated with blood pressure tracking in the Framingham Heart Study

BACKGROUND

Abnormal potassium homeostasis accompanies many secondary forms of hypertension as well as uncommon inherited, monogenic forms of hypertension. We hypothesized that serum potassium may be associated with longitudinal tracking of blood pressure (BP) and development of hypertension.

METHODS

A total of 2358 participants (1292 women, 1066 men) in the Framingham Heart Study who were free of hypertension, were not taking drugs affecting potassium homeostasis, and had serum potassium measured in 1979 to 1983 were followed for longitudinal tracking of BP and development of hypertension at examination 4 years later. Progression of BP stage was defined as an increment of one or more BP category, as defined by the sixth report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-VI), between baseline and follow-up examinations.

RESULTS

At baseline, there were no differences in systolic or diastolic BP across serum potassium quartiles. Over 4 years of follow up, 37% (457 women, 412 men) of subjects progressed by one or more JNC-VI BP category. In a logistic regression model adjusting for multiple confounders, serum potassium quartile was not associated with risk of BP progression. During follow-up, 14% (162 women, 175 men) of subjects progressed to hypertension. After adjustment for multiple confounders, there was no significant association between serum potassium quartile and risk for progression to hypertension.

CONCLUSIONS

In our community-based study sample, serum potassium was not associated with current BP, longitudinal BP tracking, or progression to hypertension.

The effect of the zeolite clinoptilolite on serum chemistry and hematopoiesis in mice

Zeolites are natural or synthetic crystalline alumosilicates with ion exchanging properties. Supplied in fodder, they promote biomass production and animal health. Our aim was to assess the effects of the natural zeolite, clinoptilolite, on hematopoiesis, serum electrolytes and essential biochemical indicators of kidney and liver function in mice. Two preparations differing in particle size were tested: a powderized form obtained by countercurrent mechanical treatment of the clinoptilolite (MTCp) and normally ground clinoptilolite (NGCp). Young adult mice were supplied with food containing 12.5, 25 or 50% clinoptilolite powder. Control animals received the same food ration without the clinoptilolite. After 10, 20, 30 and 40 days, six animals from each group were exsanguinated to obtain blood for hematological and serum for biochemical measurements as well as to collect femoral bone marrow for determination of hematopoietic activity. Clinoptilolite ingestion was well tolerated, as judged by comparable body masses of treated and control animals. A 20% increase of the potassium level was detected in mice receiving the zeolite-rich diet, without other changes in serum chemistry. Erythrocyte, hemoglobin and platelet levels in peripheral blood were not materially affected. NGCp caused leukocytosis, with concomitant decline of the GM-CFU content in the bone marrow, which was attributed to intestinal irritation by rough zeolite particles. The mechanically treated clinoptilolite preparation caused similar, albeit less pronounced, changes. In a limited experiment, mice having transplanted mammary carcinoma in the terminal stage showed increased potassium and decreased sodium and chloride levels, severe anemia and leukocytosis, decreased bone marrow cellularity and diminished content of hematopoietic progenitor cells in the marrow. The clinoptilolite preparations ameliorated the sodium and chloride decline, whereas the effects on hematopoiesis were erratic.

Spurious estimations of sodium removal during CAPD when [Na](+) is measured by Na electrode methodology

BACKGROUND

The aim of this study was to investigate the effect of pH and glucose concentration on sodium removal and the dialysate and plasma sodium ratio (D/PNa) as measured by means of a flame photometer (NaF) or direct ion-selective electrode (NaE) in continuous ambulatory peritoneal dialysis (CAPD).

METHODS

In vitro, glucose concentration, pH, NaF, and NaE were measured in fresh peritoneal dialysis solutions (PDSs) before and after the addition of glucose or KOH. In vivo, 66 four-hour peritoneal equilibration tests were performed in 35 patients on CAPD using a low pH PDS with a glucose concentration of 3.86%.

RESULTS

In vitro, NaF and NaE were significantly influenced by the glucose concentration and pH of the PDS. In vivo, in fresh PDS, there was a significant difference between the NaF and NaE results; the respective median values were 132.1 (interquartile range 129.3 to 137.5) versus 138.0 (134.4 to 141.5) mmol/L (P < 0.0001). The D/PNa ratio calculated by NaE was significantly lower than that calculated by NaF (0.88 +/- 0.03 vs. 0.91 +/- 0.04 and 0. 90 +/- 0.03 vs. 0.94 +/- 0.04 at 60 and 240 min, respectively, P < 0.0001), whereas there was no significant difference between the NaE and NaF values after correction for plasma water and a Donnan factor of 0.96 (0.88 +/- 0.03 vs. 0.88 +/- 0.04 and 0.90 +/- 0.03 vs. 0.91 +/- 0.04, P < 0.3473). Sodium removal was significantly lower when calculated as NaE than when calculated as NaF (43.9 +/- 32.7 vs. 61.0 +/- 32.2 mmol, P < 0.0001).

CONCLUSIONS

The fresh PDS sodium concentration can be corrected using a glucose concentration-related factor. The D/PNa ratio calculated as NaE or NaF is not different after correction for plasma water and a Donnan factor of 0.96. Sodium removal must be measured by means of NaF rather than NaE. This could have an important clinical impact.

Dynamics and consequences of potassium shifts in skeletal muscle and heart during exercise

Since it became clear that K(+) shifts with exercise are extensive and can cause more than a doubling of the extracellular [K(+)] ([K(+)](s)) as reviewed here, it has been suggested that these shifts may cause fatigue through the effect on muscle excitability and action potentials (AP). The cause of the K(+) shifts is a transient or long-lasting mismatch between outward repolarizing K(+) currents and K(+) influx carried by the Na(+)-K(+) pump. Several factors modify the effect of raised [K(+)](s) during exercise on membrane potential (E(m)) and force production. 1) Membrane conductance to K(+) is variable and controlled by various K(+) channels. Low relative K(+) conductance will reduce the contribution of [K(+)](s) to the E(m). In addition, high Cl(-) conductance may stabilize the E(m) during brief periods of large K(+) shifts. 2) The Na(+)-K(+) pump contributes with a hyperpolarizing current. 3) Cell swelling accompanies muscle contractions especially in fast-twitch muscle, although little in the heart. This will contribute considerably to the lowering of intracellular [K(+)] ([K(+)](c)) and will attenuate the exercise-induced rise of intracellular [Na(+)] ([Na(+)](c)). 4) The rise of [Na(+)](c) is sufficient to activate the Na(+)-K(+) pump to completely compensate increased K(+) release in the heart, yet not in skeletal muscle. In skeletal muscle there is strong evidence for control of pump activity not only through hormones, but through a hitherto unidentified mechanism. 5) Ionic shifts within the skeletal muscle t tubules and in the heart in extracellular clefts may markedly affect excitation-contraction coupling. 6) Age and state of training together with nutritional state modify muscle K(+) content and the abundance of Na(+)-K(+) pumps. We conclude that despite modifying factors coming into play during muscle activity, the K(+) shifts with high-intensity exercise may contribute substantially to fatigue in skeletal muscle, whereas in the heart, except during ischemia, the K(+) balance is controlled much more effectively.

Role of sodium in hemodialysis

Sodium chloride is the most abundant salt in extracellular fluid. In normal individuals, the tonicity exerted by dissolved sodium chloride determines plasma osmolality and indirectly determines intracellular tonicity and cell volume. Uremic patients retain nitrogenous wastes and have an elevated plasma osmolality. While urea exhibits osmotic activity in serum, no sustained gradient can be established across cell boundaries because it readily diffuses through cell membranes. Thus, sodium remains the major indicator of body tonicity and determines the distribution of water across the intracellular-extracellular boundary, subsequent cell volume, thirst, and, among patients with renal insufficiency, systemic blood pressure. As a result of highly conserved plasma tonicity control systems, uremic subjects demonstrate remarkable stability of their serum sodium. Dialysate is a synthetic interstitial fluid capable of reconstituting extracellular fluid composition through urea extraction and extremely efficient solute and solvent (salt and water) transfer to the patient. Subtle transdialyzer gradients deliver and remove large quantities of trace elements, solvent, and solute to patients, creating a variety of dialysis "disequilibrium" syndromes manifest as cellular and systemic distress. Every dialysis patient uses dialysate, and the most abundant chemicals in dialysate are salt and water. Despite its universal use, no consensus on dialysate composition or tonicity exists. This can only be explained if we believe that dialysate composition is best determined by matching unique dialysis delivery system characteristics to specific patient requirements. Such a paradigm treats dialysate as a drug and the dialysis system as a delivery device. Understanding the therapeutic and toxic profiles of this drug (dialysate) and its delivery device (the dialyzer) is important to safe, effective, goal-directed modifications of therapy. This article explores some of the historical rationale behind choosing specific dialysate tonicities.

External quality assessment in clinical chemistry: review of the situation in Croatia with particular reference to equipment

The effect of the use of new flame photometers (Ciba Corning 480, Chiron, Salzburg, Austria) and multichannel analyzers (BM Hitachi 904 or BM Hitachi 911, both Boehringer GmbH, Mannheim, Germany) on analytical quality was assessed in a number of medical biochemical laboratories (n=58) at health centers and general hospitals that provide primary health care services for the respective catchment areas. The laboratories were supplied during 1996 and 1997 with new equipment, as part of the First Croatian Health Project, Primary Health Care Subproject, carried out by the Croatian Ministry of Health and Croatian Institute of Health Insurance. We evaluated analytical performance of these laboratories for 19 analytes, according to the results reported in the Croatian External Quality Assessment Program for medical biochemical laboratories, performed four times per year. Changes of percentages of particular methods used by the participating laboratories were observed for inorganic phosphate, total bilirubin, urea and creatinine. Such changes were even more pronounced for enzymes, where changes in the measurement procedure such as incubation temperature and buffers were observed in the methods used. Evaluation of method performance revealed that after the introduction of new equipment interlaboratory variation decreased, so that an increasing proportion of laboratories included in the Project produced results within the target limits.

Pediatric reference intervals for 34 biochemical analytes in urban school children and adolescents

Concentrations of 34 biochemical constituents of sera were determined on 998 randomly selected urban school children and adolescents aged 8-18 years from Zagreb, Croatia. Reference intervals were obtained by using non-parametric methods to estimate 2.5 and 97.5 percentiles of distribution as upper and lower normal reference intervals, according to the IFCC recommendations. These were compared to reference intervals in the healthy adult population, aged 20-30 years from the same geographical area. Serum glucose, potassium, sodium, chloride, magnesium, iron, zinc, total serum proteins and electrophoretic fractions, and amylase, did not show age or sex differences; total serum bilirubin, total calcium, phosphate, high density lipoprotein cholesterol, total iron binding capacity, unsaturated iron binding capacity, copper, aspartate aminotransferase, alkaline phosphatase, cholinesterase, creatine kinase, and lactate dehydrogenase had higher reference intervals than the adult population. Urea, creatinine, urate, alanine aminotransferase, gamma-glutamyltransferase, total cholesterol and low density lipoprotein-cholesterol, and triglycerides had lower reference intervals than the adult population.

Dialysate sodium delivery can alter chronic blood pressure management

Low dialysate sodium concentrations can reduce postdialysis thirst and serum sodium activity, but patients typically experience dialysis hypotension, fatigue, disequilibrium, and cramps. "High-sodium" hemodialysis minimizes dialysis disequilibrium but increases the serum sodium activity of most patients. Programmed "variable-sodium" dialysis can minimize dialysis discomfort but may also alter the sodium kinetics from those of "high-sodium" dialysis. We designed a cross-over study with random order assignment to determine whether a "variable-sodium" dialysis program could reduce the blood pressure of dialysis patients without increasing dialysis morbidity. Dialysis with a dialysate sodium of 140 mEq/L was compared with dialysis with a programmed exponential decrease of dialysate sodium from 155 mEq/L to 135 mEq/L. Dialysate sodium was then held constant at 135 mEq/L for the final half hour of dialysis. Eighteen patients completed the 7-month study, each receiving 3.5 months of experimental and 3.5 months of standard therapy. Programmed "variable-sodium" dialysis resulted in a reduction in antihypertensive drug use without alterations in predialysis blood pressure, interdialytic weight gain, ultrafiltration tolerance, or the frequency of symptomatic dialysis cramps or hypotension. Patients did, however, have lower postdialysis standing blood pressures and higher postdialysis target weights during programmed "variable-sodium" dialysis.

Determination of inorganic ions of clinical interest: state-of-the-art and trends

An overview is presented of techniques, analysers and methods currently available for the determination of inorganic ions of interest in clinical laboratories; methods include those based on activation and inhibition of enzymatic reactions by these target analytes. The foreseeable, trends in this area are also discussed.

Sodium modeling in hemodiafiltration

A computer model was developed to simulate sodium and water kinetics during hemodiafiltration (HDF), acetate-free biofiltration (AFB) and hemodialysis (HD). Multiple regression analysis of the results of 3,240 simulated applications of the model (1,620 HDF, 1,080 AFB, 540 HD) showed that, during HDF and AFB, there is a close correlation (R2 = 0.92 and 0.91) between plasma water sodium concentration [( Na+P]) and a set of three variables: 1) the sodium gradient between plasma water and dialysate, 2) the sodium concentration of the substitution fluid and 3) ultrafiltration (UF) rate. With HD, a close correlation (R2 = 0.94) was found between changes in [Na+P] and combined changes in sodium gradient and the UF rate. On this basis, a regression equation was formulated for each procedure which allowed a reliable prediction of final [Na+P] to be made on the basis of knowledge of the imposed Na gradient, the programmed infusion (during HDF and AFB), and the UF rate. Clinical validation of the model was obtained in 12 patients: predicted final [Na+P] agreed well with the values measured by means of direct potentiometry (141.9 vs. 142.1 mEq/liter; P = NS), with a mean difference (-0.16 mEq/liter) and limits of agreement (+0.8 to -1.03 mEq/liter) fully acceptable for clinical purposes.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudohyponatremia: a reappraisal

Pseudohyponatremia is a falsely low serum sodium measurement. It occurs in cases of extreme hyperlipidemia or hyperproteinemia when serum sodium is measured by some--but not all--laboratory methods. This article reviews the most common techniques for measuring serum sodium levels, explains why pseudohyponatremia occurs, and identifies specific situations in which pseudohyponatremia can lead to dangerous errors in patient management. The review describes the dramatic change in prevalence of the different laboratory methods for measuring serum sodium over the past decade, and emphasizes the need for clinicians to be familiar with the methods of their clinical laboratory in order to properly interpret a reported serum sodium determination. I offer recommendations for the rational use of the different laboratory methods in various clinical situations.

Plasma sodium and potassium measurement: minimising ISE-flame differences using specimens from patients

Experience in clinical chemistry of direct reading ion-selective electrode analysers for the measurement of plasma Na+ and K+ concentrations has shown that the results obtained on any specimen may vary significantly from one make of instrument to another. To overcome these differences, the European Working Group on ISEs of the IFCC Expert Panel on pH, Blood Gases and Electrolytes have proposed that instruments should be standardised to report Na+ and K+ concentrations in undiluted plasma to agree with flame emission spectrometry in samples with normal plasma water bicarbonate concentrations and normal pH. In designing and setting the calibration of a new ISE analyser for Na+ and K+, the Corning 614, the manufacturer has attempted to satisfy this proposal using a large number of specimens obtained from patients. This paper presents details of the procedure used and the results of an independent evaluation of its validity in routine clinical practice.

Problems with measurements caused by high concentrations of serum solids

There have been numerous reports of spectrophotometric and volume problems caused by elevated levels of lipids in blood. The offending lipids, primarily triglycerides, not only cause turbidity leading to optical aberrations when added to analytical reagents, but also result in short-sampling errors leading to the measurement of inaccurate volumes of sample. Numerous methods have been developed to clear the lipemia, including ultracentrifugation organic solvent extraction, chemical precipitation and, most recently, enzymic hydrolysis. Although the latter procedures eliminate the optical problems, they do not deal with the volume dilution error created by the triglycerides. In turn, corrective mathematics have been developed to compensate for the inaccurate pipetting caused by the elevated lipids in a sample; however, these empirical calculations are not truly accurate at high concentrations of total lipids. This monograph will describe the problems caused by the presence of elevated lipids and the means available for treating them.