Creatininium reference intervals for corrected methods

Reference intervals for 12 clinical laboratory tests in a Danish population: The Lolland-Falster Health Study

Reference intervals (RIs), developed as part of the Nordic Reference Interval Project 2000 (NORIP) are widely used in most European laboratories. We aimed to examine the validity of the NORIP RIs by establishing RIs for 12 frequently used laboratory tests based on data from a local Danish population and compare these local RIs with the NORIP RIs. Using an a posteriori direct sampling approach, blood sample data were assessed from 11,138 participants aged 18+ years in the Lolland-Falster Health Study (LOFUS), of whom 2154 turned out to meet criteria for being healthy for inclusion in establishing RIs according to the NORIP methodology. The 2.5th and 97.5th percentiles were calculated for alanine aminotransferase (ALAT), albumin, alkaline phosphatase, bilirubin, creatinine, hemoglobin, high-density lipoprotein cholesterol, iron, low-density lipoprotein cholesterol, thrombocytes, total cholesterol, and triglycerides. When comparing our estimates with the NORIP, the lower reference limits (RLs) for bilirubin and iron were lower, and higher for ALAT, thrombocytes and triglycerides. Upper RLs were lower for albumin (males and females ≥70 years), bilirubin and iron, but higher for alkaline phosphatase, triglycerides and for creatinine in men. In LOFUS, approximately 20% of the participants were healthy and qualified for inclusion in the establishment of RIs. Several of the local RIs differed from the NORIP RIs.

Lower creatinine concentration values and lower inter-laboratory variation among Swedish hospital laboratories in 2014 compared to 1996: results from the Equalis external quality assessment program

Background

Creatinine measurement for estimation of glomerular filtration rate (GFR) is a frequently used laboratory test. Differences in analytic creatinine methods have caused large inter-laboratory variation. International and national standardization efforts have been made in the last decade.

Methods

This study describes the results of the standardization efforts in Sweden by summarizing data for creatinine concentration in blood plasma in the Equalis quality assessment program during 1996–2014.

Results

Non-compensated Jaffe methods dominated in 1996–2001 (91 of 103 laboratories; 90%) and were then gradually replaced by either compensated Jaffe methods or enzymatic creatinine methods. In 2014 a majority of Swedish hospital laboratories (139 of 159; 87%) used enzymatic methods. The reported mean creatinine value by the Swedish laboratories was about 10 μmol/L higher than the isotope dilution mass spectrometry (IDMS) assured reference value in 2003, but consistent with the reference value from 2009 to 2014. The inter-laboratory CV was 7%–9% for creatinine values until 2007, and thereafter gradually decreased to about 4%–5% in 2014.

Conclusions

The introduction of enzymatic methods in Swedish laboratories has contributed to achieving a low inter-laboratory variation. Also, the reported values are lower for enzymatic methods compared to Jaffe methods, and the values obtained with enzymatic methods were consistent with IDMS certified values established at reference laboratories. Thus, many Swedish hospital laboratories reported 10 μmol/L lower, and more true, creatinine concentrations in 2012 than in 2003, which may cause bias in longitudinal studies.

Challenges in the measurement of plasma creatinine on the Roche cobas c702

The aim of this study was to document the differences between two Roche creatinine measurement methods, the CREP2 test on the cobas c702 and the CREA PLUS test on the Modular P. Samples with creatinine isotope dilution mass spectrometry (IDMS) values were analyzed on both instruments. Method comparison using the remaining plasma samples was performed twice, using two different lot numbers of reagents and two different lot numbers of calibrators on both instruments. Medians and percentiles of the plasma creatinine values produced on the Modular P and cobas c702 from 2012 to 2017 were compared. The recovery of samples with IDMS creatinine values (SRM 967a level 1, SRM 967a level 2, serum X and five serum pools from Roche) was 101.7%-110.2% on the cobas c702 and 98.9%-102.6% on the Modular P. Comparison of the two methods showed that the slope was close to 1.0 using linear, Deming and Passing Bablok regressions, but all equations showed a negative intercept, indicating that the cobas c702 overestimates plasma creatinine in relation to the Modular P by 4-6 µmol/L. The median value for routine plasma creatinine lies between 74 and 77 µmol/L for the Modular P and 81 µmol/L for the cobas c702. After the cobas c702 was factorized in September 2016, the median plasma creatinine value decreased to 75 µmol/L. In conclusion, the CREP2 method on the cobas c702 overestimates creatinine by 4-6 μmol/L, which has a significant influence on the estimated glomerular filtration rate (eGFR) in children.

Should total calcium be adjusted for albumin? A retrospective observational study of laboratory data from central Norway

OBJECTIVES

Albumin-adjusted total calcium is often used as a surrogate marker for free calcium to evaluate hypocalcaemia or hypercalcaemia. Many adjustment formulas based on simple linear regression models have been published, and continue to be used in spite of questionable diagnostic accuracy. In the hope of finding a more pure albumin effect on total calcium, we used multiple linear regression models to adjust for other relevant variables. The regression coefficients of albumin were used to construct local adjustment formulas, and we tested whether the diagnostic accuracy was improved compared with previously published formulas and unadjusted calcium.

DESIGN

A retrospective hospital laboratory data study.

DATA SOURCES

The local hospital laboratory data system.

SETTING

Norway, 2006-2015.

PARTICIPANTS

6549 patients above 2 years of age, where free calcium standardised at pH 7.40, total calcium, creatinine, albumin and phosphate had been analysed in a single blood draw, including hospitalised patients and patients from outpatient clinics and general practice.

MAIN OUTCOME MEASURES

Diagnostic accuracy by Harrell's c and receiver operating characteristic curve analysis, using free calcium standardised at pH 7.40 as a gold standard, in subgroups with estimated glomerular filtration rate (eGFR) ≥60 or <60 mL/min/1.73 m².

RESULTS

In the subgroup with eGFR <60 mL/min/1.73 m², the Harrell's c of unadjusted total calcium (0.801) was significantly larger than those of the local formulas (0.790, p=0.002) and the best formula taken from literature (0.791, p=0.004). In the subgroup with eGFR ≥60 mL/min/1.73 m², no significant differences were found between these three formulas.

CONCLUSIONS

Our study shows that the diagnostic accuracy of unadjusted total calcium is superior to several commonly used adjustment formulas, and we suggest that the use of such formulas should be abandoned in clinical practice. If the clinician does not trust total calcium to reflect the calcium status of the patient, free calcium should be measured.

Biomonitoring of trace elements in urine samples of children from a coal-mining region

Biomonitoring through urine samples is important for evaluating environmental exposure, since urine is the main form of excretion for most chemical elements. Children are considered more vulnerable to adverse environmental conditions, especially children in developing countries. This study aimed to biomonitor trace elements in urine samples in children from a coal-mining region in the extreme south of Brazil. A cross-sectional study was conducted on 96 children between 6 and 11 years of age. Socioeconomic data and urine samples were collected to estimate the concentration of iron, zinc, selenium, lead, and cadmium. The prevalence of metals above the reference values was 52.0% for Se, followed by 15.6% for Zn. The data point toward a vulnerability to adverse environmental conditions in these children. Although the concentrations of the elements did not reveal intoxication cases, biomonitoring should be carried out continuously in order to assess exposure to metals and ensure the health of the population. This article provides data that help determine natural levels of metallic elements in children, specifically in South America, which have not yet been established.

Reference intervals for plasma cystatin C and plasma creatinine in adults using methods traceable to international calibrators and reference methods

INTRODUCTION

The aim of this study was to establish reference intervals for plasma cystatin C and creatinine in adults using the Gentians cystatin C method traceable to the international calibrator standard ERM-DA471/IFCC and a creatinine method traceable to the IDMS (Isotope Dilution Mass Spectrometry) creatinine reference method.

METHODS

Blood samples were collected from 304 healthy blood donors (152 men and 152 women between 17 and 66 years old) with 30-31 men and 30-31 women in each ten-year interval. Plasma cystatin C was analyzed using the Gentian Cystatin C assay on a Roche cobas c702 analyzer, and plasma creatinine was analyzed using the CREA Plus assay on the Roche Modular P analyzer.

RESULTS

The nonparametric reference intervals for plasma cystatin C were 0.58-1.00 mg/L in women (median 0.78 mg/L, range 0.56-1.06 mg/L) and 0.62-1.04 mg/L in men (median 0.79 mg/L, range 0.61-1.07 mg/L). The Mann-Whitney U test revealed no gender-related difference in plasma cystatin C (P = .21). A common reference interval in women and men was calculated to be 0.61-1.01 mg/L (median 0.79 mg/L, range 0.56-1.07 mg/L). The nonparametric reference interval for plasma creatinine was 52-89 μmol/L in women (median 69 μmol/L, range 52-92 μmol/L) and 61-108 μmol/L in men (median 86 μmol/L, range 56-118 μmol/L). The Mann-Whitney U test revealed a gender-related difference in plasma creatinine (P < .0001).

CONCLUSION

In conclusion, we have established reference intervals for plasma cystatin C and creatinine in adults using methods traceable to international standards.

Is low pre-transplant parathyroid hormone a risk marker for cardiovascular disease in long-term follow-up of renal transplant recipients?

Background

Secondary hyperparathyroidism and altered levels of parathyroid hormone (PTH) are associated with vascular events in chronic kidney disease. After renal transplantation, this association is not clear. Pre-transplant parathyroidectomy (PTX) is common, but post-transplant data are scarce. We aimed to study the effect of PTH at the time of transplantation on risk of post-transplant vascular events in renal transplant recipients with and without pre-transplant PTX.

Methods

258 patients from two Swedish transplant units were followed for 6 years. Separate analyses were made for patients with or without pre-transplant PTX. Patients with no pre-transplant PTX were stratified by quartiles of PTH at time of transplantation and patients with pre-transplant PTX were stratified by above and below median levels of PTH at time of transplantation. Hazard ratios for vascular events, mortality, and graft failure were calculated in adjusted Cox regression models.

Results

In patients with no pre-transplant PTX, the lowest quartile of PTH at transplantation had a higher risk of cardiovascular events compared to quartile 3 with an adjusted hazard ratio (95% CI) of 2.63 (1.04–6.67). In patients with pre-transplant PTX, the group below median of PTH had a higher risk of cardiovascular events with an adjusted hazard ratio (95% CI) of 18.15 (1.62–203.82) compared to patients above median of PTH.

Conclusion

Low levels of parathyroid hormone before transplantation were associated with increased risk of post-transplant vascular events both in patients with and without pre-transplant parathyroidectomy. Any conclusions on causal or direct effect of PTH on outcome cannot be drawn from this observational study.

The relationship between three eGFR formulas and hospitalization for heart failure in 54 486 individuals with type 2 diabetes

OBJECTIVE

This study aims to study the association between renal function and hospitalization for heart failure (HF) in individuals with type 2 diabetes.

METHODS

Renal function was determined according to three formulas used to estimate glomerular filtration rate (eGFR): Cockcroft-Gault, modified diet in renal disease (MDRD) and chronic kidney disease epidemiology (CKD-EPI). Proportional hazards regression models adjusted for age, sex, HbA_1c , blood pressure, smoking and cardiovascular comorbidities were constructed for each eGFR formula to estimate risk of hospitalization for heart failure. Systematic pairwise likelihood ratio tests of nested models were used to compare the predictive power of each eGFR formula.

RESULTS

In 54 486 patients, evaluated over a median follow-up of 7.0 years, a total of 5936 (10.9%) developed heart failure, with an excess risk in all eGFR categories below 60 mL/min/1.73 m² (reference: eGFR >90 mL/min/1.73 m² ). Hazard ratios ranged from 1.25 to 1.35 for eGFR 45-60 mL/min/1.73 m² , 1.62 to 1.66 for eGFR 30-45 mL/min/1.73 m² and 2.18 to 2.52 for eGFR <30 mL/min/1.73 m² in the three eGFR formulas. In pairwise comparisons, the model with the MDRD variable added significantly more information than the Cockcroft-Gault variable. For the model with the CKD-EPI variable, no clear differences in predictive power for HF hospitalization existed in relation to the other eGFR formulas.

CONCLUSION

Patients with type 2 diabetes, with eGFR 45 to 60 mL/min/1.73 m² , have approximately 25-35% increased risk of hospitalization for HF, increasing with lower eGFR, to 2-2.5 times in those with eGFR <30 mL/min/1.73 m² . The MDRD formula for calculating eGFR is more predictive of hospitalization for heart failure than the Cockcroft-Gault formula. Copyright © 2016 John Wiley & Sons, Ltd.

Short-term mortality risk of serum potassium levels in acute heart failure following myocardial infarction

AIMS

Diuretic treatment is often needed in acute heart failure following myocardial infarction (MI) and carries a risk of abnormal potassium levels. We examined the relation between different levels of potassium and mortality.

METHODS AND RESULTS

From Danish national registries we identified 2596 patients treated with loop diuretics after their first MI episode where potassium measurement was available within 3 months. All-cause mortality was examined according to seven predefined potassium levels: hypokalaemia <3.5 mmol/L, low normal potassium 3.5-3.8 mmol/L, normal potassium 3.9-4.2 mmol/L, normal potassium 4.3-4.5 mmol/L, high normal potassium 4.6-5.0 mmol/L, mild hyperkalaemia 5.1-5.5 mmol/L, and severe hyperkalaemia: >5.5 mmol/L. Follow-up was 90 days and using normal potassium 3.9-4.2 mmol/L as a reference, we estimated the risk of death with a multivariable-adjusted Cox proportional hazard model. After 90 days, the mortality rates in the seven potassium intervals were 15.7, 13.6, 7.3, 8.1, 10.6, 15.5, and 38.3%, respectively. Multivariable-adjusted risk for death was statistically significant for patients with hypokalaemia [hazard ratio (HR): 1.91, confidence interval (95%CI): 1.14-3.19], and mild and severe hyperkalaemia (HR: 2, CI: 1.25-3.18 and HR: 5.6, CI: 3.38-9.29, respectively). Low and high normal potassium were also associated with increased mortality (HR: 1.84, CI: 1.23-2.76 and HR: 1.55, CI: 1.09-2.22, respectively).

CONCLUSION

Potassium levels outside the interval 3.9-4.5 mmol/L were associated with a substantial risk of death in patients requiring diuretic treatment after an MI.

Using the likelihood ratio to evaluate allowable total error – an example with glycated hemoglobin (HbA1c)

Allowable total error is derived in many ways, often from data on biological variation in normal individuals. We present a new principle for evaluating allowable total error: What are the diagnostic consequences of allowable total errors in terms of errors in likelihood ratio (LR)? Glycated hemoglobin A

We estimated a function for LR of HbA

Measuring HbA

These principles of evaluating allowable total error can be applied to any diagnostically used analyte where the distribution of the analyte’s concentration is known in patients with and without the disease in a clinically relevant population. In the example used, the allowable total error of 6% leads to very erroneous LRs, suggesting that the NGSP limits of ±6% are too liberal.

Lower hemoglobin with lower ferritin: It is not just a question of anemia

AIM

To study the association between blood hemoglobin concentration (b-hemoglobin) and serum ferritin concentration (s-ferritin) in an ambulant patient population without inflammation and with normal kidney function.

METHODS

In ambulant, adult patients with normal values of s-CRP and s-creatinine, median b-hemoglobin and the fraction with anemia was compared in groups with lower s-ferritin from a level of 100 μg/L. The 10, 50 and 90 percentiles of b-hemoglobin were modelled as functions of s-ferritin using quantile regression.

RESULTS

Among 3206 women the entire b-hemoglobin distribution was shifted downwards in patients with s-ferritin less than 20 μg/L. Accordingly, the median b-hemoglobin was statistically significantly lower and the fraction with anemia was higher. In 1246 men the findings were similar, except that the turning point toward lower b-hemoglobin was at a s-ferritin level of 30 μg/L.

CONCLUSIONS

Low s-ferritin is associated with decreased b-hemoglobin in many more subjects than those labelled anemic.

Renal function in a large cohort of metformin treated patients with type 2 diabetes mellitus

Objectives

To survey renal function in a defined population on metformin treatment.

Methods

All patients in the city of Malmö who collected at least three prescriptions of metformin during two years were identified from a central registry at the National Board of Health and Welfare in Sweden. Estimated glomerular filtration rate (eGFR), from the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, of 5,408 patients were compared with a control population (n=2,815) from the same town. All cases of severe lactic acidosis leading to intensive care unit admission were also sought.

Results

In patients >79 years of age, 38% and 12% of patients had a best recorded eGFR registered below 60 and 45 ml/min/1.73 m2 respectively. In the age group 70–79 years the corresponding figures were 16% and 3% respectively. The eGFR was significantly higher in metformin treated patients than in control subjects in each age group. Three cases of lactic acidosis were recorded during the 2-year period studied. No patient with lactic acidosis was found in the highest age group.

Conclusions

In spite of reduced and fluctuating GFR in elderly patients, treatment with metformin is feasible. Adjusting the dose of metformin to renal function and adequately informing the patient could enable continuous treatment in moderately reduced GFR.

Estimating the glomerular filtration rate using serum cystatin C levels in patients with spinal cord injuries

STUDY DESIGN

Prospective cohort study.

OBJECTIVES

To investigate the relationship between (51)chromium-ethylene-diamine-tetra-acetate ((51)Cr-EDTA) clearance, serum cystatin C (CysC), serum creatinine, creatinine clearance and estimated glomerular filtration rate (eGFR(MDRD), MDRD stands for modification of diet in renal disease) based on the serum creatinine in patients with complete or incomplete spinal cord injury (SCI) and to develop and evaluate a GFR-estimating equation using serum CysC.

SETTINGS

Spinal Cord Injury Unit, Viborg Regional Hospital, Viborg, Denmark.

METHODS

Ninety-eight men and 47 women with SCI were included in the study. Serum CysC levels were measured by an automated particle-enhanced nephelometric immunoassay, serum and urine creatinine levels were measured by an enzymatic method traceable to the IDMS creatinine reference method, and (51)Cr-EDTA clearance was measured by a multiple plasma sample method.

RESULTS

The area under the curves (AUCs) in the non-parametric receiver operating characteristics (ROC) plots for serum CysC were compared with serum creatinine and to eGFR(MDRD) and revealed a significant difference (P-value < 0.05) for all SCI patients. There was no significant difference between the AUC for serum CysC compared with the AUC for creatinine clearance. GFR (ml min(-1) per 1.73 m(2)) can be calculated from serum CysC values (mg l(-1)) using the equation eGFR(CysC) = 212·exp(0.914·CysC). The model accurately predicted the GFR of 88% of patients within ± 30% of the measured GFR, and it was able to predict the GFR of 50% of patients within ± 10% of the measured GFR.

CONCLUSION

In patients with SCI, GFR can be estimated independent of age, sex and muscle mass by a newly developed equation based on a single serum CysC value.

Improved estimation of glomerular filtration rate (GFR) by comparison of eGFRcystatin C and eGFRcreatinine

OBJECTIVE

GFR-prediction equations based upon cystatin C and creatinine have better diagnostic performance in estimating GFR than equations based upon only one of the two markers. The present work concerns in what way a comparison between separate estimations of GFR based upon cystatin C (eGFR(cystatin C)) or creatinine (eGFR(creatinine)) can be used to evaluate the diagnostic performance of a combined cystatin C- and creatinine-based estimation of GFR.

METHODS

The difference between eGFR(cystatin C) and eGFR(creatinine) was compared with measured GFR (iohexol clearance) and a combined cystatin C- and creatinine-based estimation of GFR in a Swedish-Caucasian cohort of 857 adult patients.

RESULTS

A difference between eGFR(cystatin C) and eGFR(creatinine) of ≥ 40% indicated a markedly reduced diagnostic performance of the combined cystatin C- and creatinine-based estimation of GFR.

CONCLUSION

Comparison of the agreement between eGFR(cystatin C) and eGFR(creatinine) can be used to evaluate the diagnostic performance of combined cystatin C- and creatinine-based estimations of GFR. If 'threshold values' for discordance are exceeded, it must be considered whether the clinical context requires the use of an invasive gold standard method to measure GFR. In some clinical contexts either creatinine or cystatin C are known to be invalidated as markers of GFR and in these situations the use of only the cystatin C- or the creatinine-based GFR estimate should be considered when the 'threshold values' are exceeded.

Biological variation of cystatin C and creatinine

OBJECTIVE

To evaluate the day-to-day biological variation of cystatin C in comparison with creatinine in healthy subjects and in patients with impaired renal function.

MATERIAL AND METHODS

Eight weekly morning blood samples were taken from 20 healthy subjects (13 females and 7 males, median age 44 years, range 25-61) and 19 patients with impaired renal function (8 females and 11 males, median age 61 years, range 35-70). Serum cystatin C was measured using Dade Behring N Latex Cystatin C assay and serum creatinine by an enzymatic method (Roche).

RESULTS

In the healthy subjects mean serum cystatin C was 0.70 mg/L (range 0.44-1.09) and mean serum creatinine 77 micromol/L (range 54-100). The analytical variance was 2.0% for cystatin C and 1.6% for creatinine. The intra-individual variance was greater for cystatin C than for creatinine (8.6% vs. 4.7%). The inter-individual variance was similar for both analytes (cystatin C 15.1% vs. creatinine 14.4%). In the patients with impaired renal function mean serum cystatin C was 1.86 mg/L (range 0.45-3.31) and mean serum creatinine 224 micromol/L (range 103-430). The analytical variance was 1.8% for cystatin C and 1.4% for creatinine. The intra-individual variance was greater for cystatin C than for creatinine (16.0% vs. 8.9%).

CONCLUSION

In the present study, the intra-individual variance was greater for cystatin C than for creatinine in both healthy subjects and in patients with impaired renal function. Accordingly, serum creatinine is the preferred marker for serial monitoring of renal function in individuals with stable muscle mass.

Standardization of p‐creatinine assays and use of lean body mass allow improved prediction of calculated glomerular filtration rate in adults: A new equation

OBJECTIVE

To evaluate the Cockcroft-Gault (CG) equation, using various body weight expressions, and the Sawyer equation in predicting glomerular filtration rate (GFR) using an enzymatic and zero-calibrated Jaffe plasma-creatinine assay, and to derive a new robust equation in adults.

MATERIAL AND METHODS

The CG weight measures included total, ideal and adjusted body weight (ABW; lowest of total and ideal) and two lean body mass (LBM) expressions, while the Sawyer equation is based primarily on LBM. Iohexol clearance was used to measure GFR. One derivation set (n = 436; enzymatic assay) was used to evaluate and bias-adjust existing equations when indicated, and to derive a new equation based on plasma-creatinine, age, gender and the body weight measure yielding the best adjusted R2. All equations were then validated in a separate set (n = 414; Jaffe assay).

RESULTS

The existing equations all performed similarly in both sets. Prediction errors of equations based on LBM showed no correlation with BMI. The CGABW and Sawyer equations performed best. The new equation with LBM yielded the highest adjusted R2. In the combined set (n = 850), its accuracy (86 %/98 % of estimates within 30 %/50 % of measured GFR) was significantly better than for the CGABW (79 %/95 %) and Sawyer equations (79 %/93 %) (p<0.001) for each 30 mL/min GFR subgroup within +/-30 % and +/-50 %, except within +/-30 % >120 mL/min. Prediction error did not correlate with BMI, age or gender.

CONCLUSION

A new creatinine-based equation derived in a mainly Caucasian patient sample is a better predictor of GFR than CG-type equations irrespective of the body weight measure used or, if bias-adjusted, when using zero-calibrated creatinine assays.

Validation of a new plasma cystatin C-based formula and the Modification of Diet in Renal Disease creatinine-based formula for determination of glomerular filtration rate

OBJECTIVE

New proposed definitions of chronic kidney disease necessitate the development and use of simple and accurate methods for estimating glomerular filtration rate (GFR). Plasma cystatin C has been shown to be a more reliable GFR marker than creatinine and formulae for estimating GFR have been reported. The purpose of this study was to validate a cystatin C-based GFR prediction equation in a different population from the derivation set but using the cystatin C assay of a single laboratory, and to compare the results with that of the creatinine-based Modification of Diet in Renal Disease (MDRD) Study equation.

MATERIAL AND METHODS

A newly presented formula based on plasma cystatin C and gender and the MDRD formula based on creatinine for estimation of GFR were validated in an unselective patient material. Single sample iohexol clearance was used as the GFR reference method in 406 consecutive patients with GFR varying from normal to poor renal function. The creatinine assay used was standardized to express true plasma creatinine.

RESULTS

Median bias (1.1%) and accuracy (79.1% of the estimates within +/-30% of iohexol clearance) of the cystatin C formula were close to the derivation set. The accuracy was significantly higher than that of the original four-variable MDRD equation (73.2%; median bias 9.8%). However, the accuracy did not differ significantly from that of the re-expressed MDRD formula (79.6%; median bias 3.2%) based on true creatinine. Both formulae performed with a low bias and acceptable accuracy up to a GFR of 90 ml/min/1.73 m(2).

CONCLUSIONS

GFR estimation based on plasma cystatin C performed equally well in the validation as in the derivation set, and was as accurate as the re-expressed MDRD creatinine-based equation.

The Lund-Malmö creatinine-based glomerular filtration rate prediction equation for adults also performs well in children

OBJECTIVE

To evaluate the clinical performance in a paediatric population of the Lund-Malmö creatinine-based glomerular filtration rate (GFR) prediction equations, primarily developed for adults.

MATERIAL AND METHOD

Iohexol clearance was used as the gold standard in 85 paediatric Caucasian patients (0.3-17 years; 37 F/48 M). One Lund-Malmö equation was based on age and gender (LM) and one included lean body mass (LM-LBM). Comparisons focused on correlation (adjusted R2), bias (median percent error) and accuracy (proportions of predicted GFR differing < or = 30% from measured GFR) (mL/min/1.73 m2). The performances were compared with those of the Modification of Diet in Renal Disease (MDRD) Study equation, a dedicated paediatric creatinine equation, Counahan-Barratt (CB) and a cystatin C-based equation.

RESULTS

The MDRD equation performed poorly with a median bias of 96%. Of the remaining equations, only the LM-LBM produced significant bias (+10% in median) according to line of identity regression analysis. The LM equation yielded marginally higher accuracy (76%) than the LM-LBM equation (74%) and the CB (73%), but lower than the cystatin C-based equation (82%). However, the estimated accuracy figures for these four equations were generally imprecise and none of the differences compared with the LM equation was statistically significant.

CONCLUSION

In contrast to most creatinine-based GFR prediction equations, the LM equation performs adequately for both children and adults. This may be due to the unique model-building principles used when the LM equation was established. Further validation in a larger paediatric population is necessary.

Prediction of relative glomerular filtration rate in adults: new improved equations based on Swedish Caucasians and standardized plasma-creatinine assays

OBJECTIVE

To evaluate newly developed equations predicting relative glomerular filtration rate(GFR) in adult Swedish Caucasians and to compare with the Modification of Diet in Renal Disease(MDRD) and Mayo Clinic equations using enzymatic and zero-calibrated plasma creatinine assays.

MATERIAL AND METHODS

GFR was measured with iohexol clearance adjusted to 1.73 m(2). One population sample (n=436/Lund) was used to derive an equation based on plasma-creatinine/age/gender, and a second with the addition of lean body mass (LBM). Both equations were validated in a separate sample (n=414/Malmö). The coefficients of the equations were eventually fine-tuned using all 850 patients and yielding Lund-Malmö equations without (LM) and with LBM-term (LM(LBM)). Their performance was compared with the MDRD(CC) (conventional creatinine calibration), MDRD(IDMS) (isotope dilution mass spectroscopy traceable calibration) and Mayo Clinic equations.

RESULTS

The Lund equations performed similarly in both samples. In the combined set, the Mayo Clinic/MDRD(CC) resulted in +19.0/+10.2 % median bias, while bias for the other equations was < 10 %. LM(LBM) had the highest accuracy (86 % of estimates within 30 % of measured GFR), significantly (p < 0.001) better than for MDRD(IDMS) (80 %). In men with BMI < 20 kg/m(2), MDRD(IDMS)/LM had +46 %/+19 % median bias. MDRD(IDMS) also overestimated GFR by 22 %/14 % in men/women above 80 years of age. The LM(LBM) equation had < 10 % bias irrespective of BMI, age or GFR except for a 15 % negative bias at GFR > 90 mL/min/1.73 m(2).

CONCLUSION

The newly developed Lund-Malmö equations for GFR estimation performed better than the MDRD(IDMS) and Mayo Clinic equations in a Swedish Caucasian sample. Inclusion of an LBM term improved performance markedly in certain subgroups.

Reference intervals for serum creatinine concentrations: assessment of available data for global application

BACKGROUND

Reference intervals for serum creatinine remain relevant despite the current emphasis on the use of the estimated glomerular filtration rate for assessing renal function. Many studies on creatinine reference values have been published in the last 20 years. Using criteria derived from published IFCC documents, we sought to identify universally applicable reference intervals for creatinine via a systematic review of the literature.

METHODS

Studies were selected for inclusion in the systematic review only if the following criteria were met: (a) reference individuals were selected using an "a priori" selection scheme, (b) preanalytical conditions were adequately described; (c) traceability of the produced results to the isotope dilution-mass spectrometry (IDMS) reference method was demonstrated experimentally, and (d) the collected data received adequate statistical treatment.

RESULTS

Of 37 reports dealing specifically with serum creatinine reference values, only 1 report with pediatric data and 5 reports with adult data met these criteria. The primary reason for exclusion of most papers was an inadequate demonstration of measurement traceability. Based on the data of the selected studies, we have collated recommended reference intervals for white adults and children.

CONCLUSION

Laboratories using methods producing traceable results to IDMS can apply the selected reference intervals for serum creatinine in evaluating white individuals.

Multicentre physiological reference values for the concentration of creatininium in plasma and diagnostic specificity of glomerular filtration rate estimated with the MDRD equation

BACKGROUND

The National Kidney Disease Education Program recommends that clinical laboratories, when asked for an estimation of glomerular filtration rate in a patient by means of the "four-variable" Modification of Diet in Renal Disease (MDRD) Study equation, also provide the measurement result for creatininium concentration in plasma and the appropriate reference interval. On the other hand, clinical laboratories seeking accreditation for compliance with ISO 15189:2003 need to demonstrate that the physiological reference intervals communicated to all users of laboratory services are appropriate for the patient population served, and for their measurement systems.

METHODS

Ten clinical laboratories in different regions of Spain collaborated in identifying reference individuals and producing reference values for the concentration of creatininium in plasma using RD/Hitachi Modular Analytics analysers, and for the volume rate of glomerular filtrate in kidneys (glomerular filtration rate), estimated with the "four-variable" MDRD Study equation. All the logistic work was carried out in co-operation with the supplier of the reagents and analysers (Roche Diagnostics España, S.L., Sant Cugat del Vallès, Catalonia, Spain). Using all the reference values obtained by each laboratory, multicentre reference limits were estimated non-parametrically.

RESULTS AND CONCLUSIONS

Reference intervals estimated in this study for concentrations of plasma creatininium are 52-85 micromol/L for women and 64-106 micromol/L for men. The diagnostic specificity of the estimated glomerular filtration rate is 99.2% when applied to healthy persons to screen for chronic kidney disease.

Plasma homocysteine, cobalamin/folate status, and vascular disease in a large population of psychogeriatric patients

BACKGROUND

Cobalamin/folate deficiency and vascular disease are prevalent in elderly subjects and may lead to mental symptoms, but may even more often influence the severity of other organic and non-organic mental diseases. In the present study, we have evaluated cobalamin-folate status and the presence of vascular disease in 1,982 psychogeriatric patients investigated and diagnosed in a psychogeriatric clinic. The objective of the present study is to obtain information on the role of cobalamin/folate status and vascular disease in different diagnoses of psychogeriatric patients and their association with plasma homocysteine (tHcy).

METHODS

We have measured serum cobalamin, blood/serum folate, serum creatinine, plasma tHcy and evaluated the presence of vascular disease in 1,982 well-defined psychogeriatric patients.

RESULTS AND CONCLUSIONS

The present study indicates that cobalamin/folate deficiencies do not play an important role in cognitive dysfunction in psychogeriatric patients, since only about 7% of the study population had metabolic cobalamin/folate deficiencies. Furthermore, cobalamin/folate deficiencies were rare in younger patients (below 70 years of age). We were also able to confirm our previous finding that there was no association between dementia of Alzheimer type (AD) and plasma tHcy level or metabolic cobalamin/folate deficiencies. Furthermore, we observed a low proportion of vascular disease in patients with AD, which does not give support for an association between well-defined AD and the presence of vascular disease. The presence of vascular disease was higher and of similar degree in patients with mild cognitive impairment and depression, which indicates an association between these diagnoses and the presence of vascular disease. The present study also shows that at plasma tHcy levels below 14 micromol/l, the likelihood of cobalamin/folate deficiency is small and further investigation of cobalamin/folate status could be omitted.