Alkalinization of urine samples preserves albumin concentrations during prolonged frozen storage in patients with diabetes mellitus

Heerspink, Hiddo J L; Nauta, Ferdau L.; Zee, C. P. van der; Brinkman, Jacoline W.; Gansevoort, Ron T.; Zeeuw, Dick de; Bakker, Stephan J. L.

doi:10.1111/j.1464-5491.2009.02721.x

Cited by 17 publications

(11 citation statements)

References 20 publications

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“…Furthermore, we measured all our markers in fresh urine samples to ensure optimal sample quality. It has previously been shown for several markers that frozen storage and freeze-thaw cycles lead to a systematic decrease and increase in variability (9,23,24), which may negatively influence association studies such as the present one. Finally, most authors investigating urinary excretion of renal damage markers did not measure plasma concentrations (9,25).…”

Section: Discussionmentioning

confidence: 80%

Glomerular and Tubular Damage Markers Are Elevated in Patients With Diabetes

et al. 2011

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OBJECTIVEWe investigated in a cross-sectional study the levels of serum and urinary damage markers in diabetic patients (n = 94) and nondiabetic control subjects (n = 45) to study the association of glomerular (IgG), proximal tubular (kidney injury molecule [KIM]-1, N-acetyl-β-d-glucosaminidase [NAG], neutrophil gelatinase–associated lipocalin [NGAL], and cystatin C), and distal tubular (heart fatty acid–binding protein [H-FABP]) damage markers with kidney disease severity, as assessed by albuminuria and estimated glomerular filtration rate (eGFR).RESEARCH DESIGN AND METHODSDamage markers were measured in triplicate in fresh morning urine samples and in plasma.RESULTSOf the diabetic patients, 41 were normoalbuminuric, 41 were microalbuminuric, and 12 were macroalbuminuric. Urinary NAG (ninefold), NGAL (1.5-fold), and H-FABP (3.5-fold) were significantly elevated in normoalbuminuric diabetic patients compared with nondiabetic control subjects. Urinary concentrations of all markers increased per albuminuria stratum, except KIM-1. All urinary damage markers, except KIM-1, were significantly associated with albuminuria, independent of age, sex, and plasma concentrations of the corresponding biomarker (standard βs between 0.35 and 0.87; all P ≤ 0.001). All urinary damage markers, except KIM-1, were significantly associated with the eGFR in univariate models (standard βs between −0.38 and −0.21; all P < 0.04). After adjusting for age, sex, plasma concentration of the corresponding damage marker, and albuminuria, only the association of H-FABP with eGFR remained significant (standard β −0.26; P = 0.037).CONCLUSIONSGlomerular and tubular markers are associated with albuminuria, independently of eGFR, suggesting that albuminuria reflects both glomerular and tubulointerstitial damage. Only urinary H-FABP is associated with eGFR independently of albuminuria and, therefore, may be a promising urinary damage marker to assess diabetic kidney disease.

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Section: Discussionmentioning

confidence: 80%

Glomerular and Tubular Damage Markers Are Elevated in Patients With Diabetes

et al. 2011

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“…The personnel measuring all the biomarkers were blinded to each patient’s clinical characteristics. Because the stability of sCysC and uNAG has already been demonstrated [25–27], urinary albumin will not degrade significantly with short-term storage [28, 29]. Preanalysis about the influence of cooling or freezing of samples was not executed.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of clinically available renal biomarkers in critically ill adults: a prospective multicenter observational study

et al. 2017

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BackgroundAlthough serum cystatin C (sCysC), urinary N-acetyl-β-d-glucosaminidase (uNAG), and urinary albumin/creatinine ratio (uACR) are clinically available, their optimal combination for acute kidney injury (AKI) detection and prognosis prediction remains unclear. We aimed to assess the discriminative abilities of these biomarkers and their possible combinations for AKI detection and intensive care unit (ICU) mortality prediction in critically ill adults.MethodsA multicenter, prospective observational study was conducted in mixed medical-surgical ICUs at three tertiary care hospitals. One thousand eighty-four adult critically ill patients admitted to the ICUs were studied. We assessed the use of individual biomarkers (sCysC, uNAG, and uACR) measured at ICU admission and their combinations with regard to AKI detection and prognosis prediction.ResultsAUC-ROCs for sCysC, uNAG, and uACR were calculated for total AKI (0.738, 0.650, and 0.683, respectively), severe AKI (0.839, 0.706, and 0.771, respectively), and ICU mortality (0.727, 0.793, and 0.777, respectively). The panel of sCysC plus uNAG detected total and severe AKI with significantly higher accuracy than either individual biomarkers or the other two panels (uNAG plus uACR or sCysC plus uACR). For detecting total AKI, severe AKI, and ICU mortality at ICU admission, this panel yielded AUC-ROCs of 0.756, 0.863, and 0.811, respectively; positive predictive values of 0.71, 0.31, and 0.17, respectively; and negative predictive values of 0.81, 0.97, and 0.98, respectively. Moreover, this panel significantly contributed to the accuracy of the clinical models for AKI detection and ICU mortality prediction, as measured by the AUC-ROC, continuous net reclassification index, and incremental discrimination improvement index. The comparable performance of this panel was further confirmed with bootstrap internal validation.ConclusionsThe combination of a functional marker (sCysC) and a tubular damage marker (uNAG) revealed significantly superior discriminative performance for AKI detection and yielded additional prognostic information on ICU mortality.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-017-1626-0) contains supplementary material, which is available to authorized users.

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“…Although our home urine collection protocol worked well in this urban population (where all participants were residents of London, Ontario, and urine samples were picked up by hospital courier), including participants from rural areas would require different arrangements for sample pick up. As well, our study sample was 88.5 % male, which is notably higher than the typical 2:3 male-to-female ratio seen in chronic kidney disease populations at our center [ 37 ] and elsewhere [ 6 , 30 ]. It is not clear whether this discrepancy is related to the study protocol or is simply a random effect of the small sample size.…”

Section: Discussionmentioning

confidence: 59%

“…While a detailed investigation into the effects of sample processing on ACR measurement was beyond the scope of this study, others have shown that laboratory assay parameters (which are not standardized across laboratories) can affect ACR measurement. These factors include freezing and thawing protocols, type of assay tube (glass, polystyrene, and polypropylene), mixing protocols before and after freezing (e.g., hand inversion, vortex-mixing, centrifuging), storage temperature (falsely low albumin concentrations have been reported for samples stored at −20 °C [ 27 – 29 ]), sample pH (where urine alkalinization to pH >8.0 can prevent sample degradation during long-term frozen storage at −20 °C [ 30 ]), and type of assay (e.g., radioimmunoassay, immunoturbidimetric, enzyme-linked immunosorbent) [ 29 ]. As well, samples with higher albumin concentrations at baseline may be less affected by long-term storage [ 26 , 27 , 30 - 32 ].…”

Section: Discussionmentioning

confidence: 99%

Consecutive First-Morning Urine Samples to Measure Change in the Albumin-to-Creatinine Ratio: A Pilot Study of a Home Urine Collection Protocol

Sontrop

Garg

et al. 2016

Can J Kidney Health Dis

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BackgroundMultiple first-morning urine samples are recommended for measuring the urine albumin-to-creatinine ratio (ACR); however, this can be challenging in community-based research.MethodsThe objectives of the study are to pilot-test a home urine collection protocol and examine how the average and variance of ACR varied with the number of urine collections and time to laboratory analysis. This is a prospective observational pilot study. This study was conducted in London, Ontario, Canada at the London Health Sciences Centre (2012–2013). The patients were adults with chronic kidney disease (mean estimated glomerular filtration rate, 36 mL/min/1.73 m2). Participants collected a first-morning 20-mL urine sample on three consecutive days. This process was repeated after 3 months. Samples were picked up by hospital courier and analyzed for ACR on the same day; additional aliquots were analyzed after a delay of 24–48 h (stored at 4 °C) and 3–9 months (stored at –80 °C). The geometric mean of the percentage change in ACR between baseline and 3 months was calculated and compared between single samples and the average of two vs. three consecutive samples.ResultsOf 31 patients enrolled, 26 (83.9 %) submitted all six urine samples. The geometric mean of ACR for three consecutive samples at baseline was 87, 83, and 80 mg/mmol, and the corresponding percentage increase from baseline to 3 months was 15 % (95 % confidence interval (CI), −9 to 46 %), 33 % (95 % CI, 10 to 59 %), and 22 % (95 % CI, −6 to 57 %). Compared with single urine collections at baseline and follow-up, averaging ACR values from two consecutive first-morning urine samples improved the sample variance and reduced the required sample size to detect a given treatment effect by approximately 30 %. No further gain in statistical efficiency was achieved with three urine samples. Results were similar when the laboratory analysis was delayed by 24–48 h, but a delay of 3–9 months resulted in systematic overestimation of the ACR. Our study’s generalizability is limited by its small sample size and reliance on a clinic-based population from a single urban center.ConclusionsWe successfully used a home urine collection protocol to obtain multiple first-morning urine samples in patients with chronic kidney disease. Statistical efficiency was improved by averaging ACR values from two consecutive first-morning urine samples at baseline and follow-up.

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Alkalinization of urine samples preserves albumin concentrations during prolonged frozen storage in patients with diabetes mellitus

Abstract: Urine alkalinization to pH > 8.0 prevents the decline in UAC associated with 12 months of frozen storage at -20 degrees C and results in lower variation between samples after storage.

Cited by 17 publications

References 20 publications

Glomerular and Tubular Damage Markers Are Elevated in Patients With Diabetes

Glomerular and Tubular Damage Markers Are Elevated in Patients With Diabetes

Evaluation of clinically available renal biomarkers in critically ill adults: a prospective multicenter observational study

Consecutive First-Morning Urine Samples to Measure Change in the Albumin-to-Creatinine Ratio: A Pilot Study of a Home Urine Collection Protocol

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