Analyzers with ion-selective electrodes (ISEs) for ionized magnesium (iMg) should yield comparable and unbiased results for iMg. This IFCC guideline on sampling, measuring and reporting iMg in plasma provides a prerequisite to achieve this goal [in this document, "plasma" refers to circulating plasma and the forms in which it is sampled, namely the plasma phase of anticoagulated whole blood (or "blood"), plasma separated from blood cells, or serum]. The guideline recommends measuring and reporting ionized magnesium as a substance concentration relative to the substance concentration of magnesium in primary aqueous calibrants with magnesium, sodium, and calcium chloride of physiological ionic strength. The recommended name is "the concentration of ionized magnesium in plasma". Based on this guideline, results will be approximately 3% higher than the true substance concentration and 4% lower than the true molality in plasma. Calcium ions interfere with all current magnesium ion-selective electrodes (Mg-ISEs), and thus it is necessary to determine both ions simultaneously in each sample and correct the result for Ca2+ interference. Binding of Mg in plasma is pH-dependent. Therefore, pH should be measured simultaneously with iMg to allow adjustment of the result to pH 7.4. The concentration of iMg in plasma may be physiologically and clinically more relevant than the concentration of total magnesium. Furthermore, blood-gas analyzers or instruments for point-of-care testing are able to measure plasma iMg using whole blood (with intact blood cells) as the sample, minimizing turnaround time compared to serum and plasma, which require removal of blood cells.

n/a

Introduction: Treatment of osteoporosis is becoming more effective, but methods to identify patients who are most suitable for investigation and treatment are still being debated. Should any type of fracture have higher priority for investigation of osteoporosis than any other? Is the number of previous fractures useful information? Material and methods: We investigated 303 consecutive women patients between 55 and 75 years of age who had a newly diagnosed low-energy fracture. They answered a questionnaire on previous fractures which also dealt with risk factors. Bone mineral density (BMD) was measured at the hip, lumbar spine, and forearm. Results: The distribution of fracture location was: distal forearm 56%, proximal humerus 12%, vertebra 18%, and hip 13%, all with similar age. Half of the subjects had had at least one previous fracture before the index fracture, 19% had had two previous fractures, and 6% had had three or more previous fractures. Patients with vertebral or hip fracture had lower BMD and had had more previous fractures than patients with forearm or humerus fractures. There was an inverse correlation between number of fractures and BMD. Osteoporosis was present in one-third of patients with forearm fracture, in one-half of those with hip or humerus fracture, and in two-thirds of those with vertebral fracture. Interpretation: Vertebral fractures were the strongest marker of low BMD and forearm fractures the weakest. The number of previous fractures is helpful information for finding the most osteoporotic patient in terms of severity. Investigation of osteoporosis therefore seems warranted in every woman between the ages of 55 and 75 with a recent low-energy fracture, with highest priority being given to those with vertebral, hip, or multiple fractures. Copyright© Taylor & Francis 2007. all rights reserved.

In current clinical practice, plasma and blood glucose are used interchangeably with a consequent risk of clinical misinterpretation. In human blood, glucose is distributed, like water, between erythrocytes and plasma. The molality of glucose (amount of glucose per unit water mass) is the same throughout the sample, but the concentration is higher in plasma, because the concentration of water and therefore glucose is higher in plasma than in erythrocytes. Different devices for the measurement of glucose may detect and report fundamentally different quantities. Different water concentrations in the calibrator, plasma, and erythrocyte fluid can explain some of the differences. Results for glucose measurements depend on the sample type and on whether the method requires sample dilution or uses biosensors in undiluted samples. If the results are mixed up or used indiscriminately, the differences may exceed the maximum allowable error for glucose determinations for diagnosing and monitoring diabetes mellitus, thus complicating patient treatment. The goal of the International Federation of Clinical Chemistry and Laboratory Medicine, Scientific Division, Working Group on Selective Electrodes and Point of Care Testing (IFCC-SD-WG-SEPOCT) is to reach a global consensus on reporting results. The document recommends reporting the concentration of glucose in plasma (in the unit mmol/L), irrespective of sample type or measurement technique. A constant factor of 1.11 is used to convert concentration in whole blood to the equivalent concentration in plasma. The conversion will provide harmonized results, facilitating the classification and care of patients and leading to fewer therapeutic misjudgments. © 2006 by Walter de Gruyter.

The proposed recommendation for measuring and reporting chloride in undiluted plasma† or blood by ion-selective electrodes (ISEs) will provide results that are identical to chloride concentrations measured by coulometry for standardized normal plasma or blood samples. It is applicable to all current ISEs dedicated to chloride measurement in undiluted samples that meet the requirements. However, in samples with reduced water concentration, results by coulometry are lower than by ion-selective electrode due to volume displacement. The quantity measured by this standardized ISE procedure is called the ionized chloride concentration. It may be clinically more relevant than the chloride concentration as determined by coulometry, photometry or by ISE after dilution of the sample. © 2006 by Walter de Gruyter.

The bone alkaline phosphatase (BALP) B1x isoform has previously only been identified in some adults with chronic kidney disease on dialysis and in human bone tissue. Twenty-nine patients, 3-20 years of age, with reduced renal function due to a variety of kidney diseases were examined. We measured parathyroid hormone (PTH), biointact (whole 1-84) PTH, osteoprotegerin (OPG), CrossLaps (CTX), tartrate-resistant acid phosphatase isoform 5b (TRACP 5b) type I procollagen intact amino-terminal propeptide (PINP), osteocalcin, total alkaline phosphatase (ALP), and BALP isoforms B/I, B1x, B1, and B2. Fifty percent higher levels were detected of PTH vs. biointact PTH, demonstrating non-(1-84) PTH fragments detected by the PTH assay. Increased activities were found in five, four, and three patients for total ALP, B1, and B2, respectively. Sixteen (55%) patients had increased B/I levels. B1x was identified in two (7%) patients, who had OPG levels in the higher range independently of age, glomerular filtration rate (GFR), and biointact PTH. B1x was identified prior to and after 9 days of growth hormone (GH) therapy in one patient but not after 1, 3, 6, and 12 months, however. In conclusion, our study demonstrates that the novel BALP B1x isoform is occasionally found to be present in children with kidney disease but to a lesser degree in comparison with adults with chronic kidney disease on dialysis. It is essential to perform bone histomorphometry for future investigations in order to elucidate the exact nature of circulating B1x in patients with kidney disease for accurate classification of type of renal bone disease. © IPNA 2006.

In current clinical practice, plasma and blood glucose are used interchangeably with a consequent risk of clinical misinterpretation. In human blood, glucose, like water, is distributed between erythrocytes and plasma. The molality of glucose (amount of glucose per unit of water mass) is the same throughout the sample, but the concentration is higher in plasma because the concentration of water and, therefore, glucose is higher in plasma than in erythrocytes. Different devices for the measurement of glucose may detect and report fundamentally different quantities. Different water concentrations in calibrators, plasma, and erythrocyte fluid can explain some of the differences. Results of glucose measurements depend on sample type and on whether methods require sample dilution or use biosensors in undiluted samples. If the results are mixed up or used indiscriminately, the differences may exceed the maximum allowable error of glucose determinations for diagnosing and monitoring diabetes mellitus, and complicate the treatment. The goal of the IFCC Scientific Division Working Group on Selective Electrodes and Point of Care Testing (IFCC-SD, WG-SEPOCT) is to reach a global consensus on reporting results. The document recommends reporting the concentration of glucose in plasma (with the unit mmol/L), irrespective of sample type or measurement technique. A constant factor of 1.11 is used to convert concentration in whole blood to the equivalent concentration in the pertinent plasma. The conversion will provide harmonized results, facilitating the classification and care of patients and leading to fewer therapeutic misjudgments. © 2005 American Association for Clinical Chemistry.

Background

Bone mineral density (BMD) is used to follow gain or loss of bone mass but cannot detect changes within a short period of time. Biochemical markers of bone turnover may be of value for prediction of individual bone loss.

Methods

We studied the relation between common inexpensive markers of bone turnover (serum alkaline phosphatase (ALP), osteocalcin (OC), urinary hydroxyproline (OHPr), and calcium (Ca)), BMD, age, and menopause in a combined cross-sectional and longitudinal design comprising 429 pre- and postmenopausal randomly selected women aged 21–79 years (mean 50 years). A follow-up was initiated after 5 years (including 192 of these women), which focused on changes in bone mass and the ability of these four common markers of bone turnover (sampled at baseline) to predict future bone loss.

Results

A marked increase was observed for all markers at the beginning of menopause. During the postmenopausal period ALP and Ca decreased to near premenopausal levels, while OC and OHPr remained high even 15 years after menopause. We also found inverse correlations at baseline between the bone markers and BMD, independent of the selected marker or skeletal site, r=−0.14 to −0.46, P<0.05. The correlations between ALP, OC, OHPr, and subsequent bone loss over 5 years, was significant for arm, r=−0.23 to −0.36, P<0.01. Baseline levels of all bone markers correlated significantly at group level with the 5-year follow-up of BMD for all sites. The ability of markers to predict individual bone loss was estimated by a multivariate regression model, which included baseline BMD, age, and body mass index as independent variables. ROC analysis showed a validity of approximately 76% for the forearm model, but was lower for the hip (55%) and lumbar spine (65%).

Conclusions

These data show that the common inexpensive biochemical markers of bone turnover ALP, OC, OHPr, and Ca were related to the current bone mass and, moreover, provides information about future bone loss at the individual level. Future investigations should include an evaluation of the clinical relevance of markers of bone turnover in relation to fracture risk.

All analyzers with ion-selective electrodes for ionized magnesium (iMg) should yield comparable and unbiased results. The prerequisite to achieve this goal is to reach consensus on sampling, measurement and reporting. The recommended guidelines for sampling, measurement and reporting iMg in plasma ("plasma" refers to circulating plasma and the forms in which it is sampled: the plasma phase of anticoagulated whole blood, plasma separated from blood cells, or serum) or blood, referring to the substance concentration of iMg in the calibrants, will provide results for iMg that are approximately 3% greater than its true concentration, and 4% less than its true molality. Binding of magnesium to proteins and ligands in plasma and blood is pH-dependent. Therefore, pH should be simultaneously measured to allow adjustment of iMg concentration to pH 7.4. The substance concentration of iMg may be physiologically and consequently clinically more relevant than the substance concentration of total magnesium. © 2005 by Walter de Gruyter.