Urinary Albumin Detection: Comparison of Two Different Methods

Chronic kidney disease in public renal practices in Queensland, Australia, 2011-2018

AIM

To describe adults with (non-dialysis) chronic kidney disease (CKD) in nine public renal practice sites in the Australian state of Queensland.

METHODS

7,060 persons were recruited to a CKD Registry in May 2011 and until start of kidney replacement therapy (KRT), death without KRT or June 2018, for a median period of 3.4 years.

RESULTS

The cohort comprised 7,060 persons, 52% males, with a median age of 68 yr; 85% had CKD stages 3A to 5, 45.4% were diabetic, 24.6% had diabetic nephropathy, and 51.7% were obese. Younger persons mostly had glomerulonephritis or genetic renal disease, while older persons mostly had diabetic nephropathy, renovascular disease and multiple diagnoses. Proportions of specific renal diagnoses varied >2-fold across sites. Over the first year, eGFR fell in 24% but was stable or improved in 76%. Over follow up, 10% started KRT, at a median age of 62 yr, most with CKD stages 4 and 5 at consent, while 18.8% died without KRT, at a median age of 80 yr. Indigenous people were younger at consent and more often had diabetes and diabetic kidney disease and had higher incidence rates of KRT.

CONCLUSION

The spectrum of characteristics in CKD patients in renal practices is much broader than represented by the minority who ultimately start KRT. Variation in CKD by causes, age, site and Indigenous status, the prevalence of obesity, relative stability of kidney function in many persons over the short term, and differences between those who KRT and die without KRT are all important to explore.

Influence of SGLT2 Inhibitor Treatment on Urine Antioxidant Status in Type 2 Diabetic Patients: A Pilot Study

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have been recognized as potent antioxidant agents. Since SGLT2i are nephroprotective drugs, we aimed to examine the urine antioxidant status in patients with type 2 diabetes mellitus (T2DM). One hundred and one subjects participated in this study, including 37 T2DM patients treated with SGLT2i, 31 T2DM patients not using SGLT2i, and 33 healthy individuals serving as a control group. Total antioxidant capacity (TAC), superoxide dismutase (SOD), manganese superoxide dismutase (MnSOD), free thiol groups (R-SH, sulfhydryl groups), and catalase (CAT) activity, as well as glucose concentration, were assessed in the urine of all participants. Urine SOD and MnSOD activity were significantly higher among T2DM patients treated with SGLT2i than T2DM patients without SGLT2i treatment (p = 0.009 and p = 0.003, respectively) and to the healthy controls (p = 0.002 and p = 0.001, respectively). TAC was significantly lower in patients with T2DM treated with SGLT2i when compared to those not treated and healthy subjects (p = 0.036 and p = 0.019, respectively). It could be hypothesized that the mechanism by which SGLT2i provides nephroprotective effects involves improvement of the SOD antioxidant activity. However, lower TAC might impose higher OS (oxidative stress), and elevation of SOD activity might be a compensatory mechanism.

About 1/3rd of north Indian patients less than 50 years of age with type 2 diabetes have high pulse wave velocity indicating high risk of atherosclerosis

BACKGROUND AND AIMS

Asian Indian patients with type 2 diabetes mellitus (T2DM) have a high cardiovascular risk even at young age. There is a need to assess this increased risk and identify atherosclerosis early so that appropriate measures for risk reduction can be taken. We aimed to study carotid-femoral pulse wave velocity (Cf-PWV), a non-invasive indicator of atherosclerosis, in patients with diabetes below 50 years of age and its correlation with markers of obesity and other cardiovascular risk factors.

METHODS

Patients (n, 299) with T2DM below 50 years of age underwent measurement of Cf-PWV by applanation tonometry. Anthropometric parameters, blood pressure, liver span, glycosylated hemoglobin, serum lipid profile, urinary microalbumin, ankle brachial index and carotid intima media thickness were measured.

RESULTS

Data show that 32.4% of patients had high Cf-PWV, with mean values higher in males than females. On stepwise multiple linear regression analysis, the significant independent determinants of PWV were age, systolic blood pressure, waist circumference, microalbumin and liver span.

CONCLUSION

About one third patients with T2DM less than 50 years of age, in north India have increased arterial stiffness which correlates with blood pressure, abdominal obesity, liver size and microalbumin, indicating increased risk for coronary artery disease.

Interlaboratory bias of albuminuria and proteinuria in hypertensive pregnancy

BACKGROUND

Measurement of proteinuria in women with hypertensive disorders of pregnancy is of major importance in the diagnosis and management of preeclampsia. Urinary protein/creatinine ratio, which is commonly used to detect kidney damage in preeclampsia, suffers from important analytical limitations, including poor harmonization of results between laboratories. Adoption of albuminuria could help reduce interlaboratory bias, since methods used to quantify it are better harmonized.

METHODS

A total of 27 urinary samples collected from hypertensive women evaluated for preeclampsia were sent to four different clinical laboratories in Canada. Urinary proteins and albumin as well as urinary creatinine were measured in duplicates in one batch to calculate protein/creatinine (PCR) and albumin/creatinine (ACR) ratio. Statistical analyses were done to evaluate interlaboratory variability of urinary proteins and urinary albumin.

RESULTS

Interlaboratory bias for urinary proteins ranged from 64.7% at low concentration to 3.9% at higher concentrations. In contrast, urinary albumin interlaboratory bias ranged from 29.2% to 4% from low to high concentrations. Coefficient of variation for urinary proteins reached a maximum of 91.5% in lower concentration while urinary albumin highest value was 42.7%. When looking at PCR and ACR ratio, eight samples had PCR measurement range that contained the diagnostic threshold used to detect kidney damage in HDP (30 mg/mmol), while only four samples had ACR ratio measurement range that contained the diagnostic threshold used outside of pregnancy in Canada (2 mg/mmol).

CONCLUSION

Interlaboratory bias was lower for urinary albumin measurement compared to urinary proteins in hypertensive women evaluated for preeclampsia. Better harmonization with the use of albumin instead of protein measurement would reduce instances where results of different laboratories lead to opposite diagnosis of kidney damage in pregnancy.

Simple Tip-Based Sample Processing Method for Urinary Proteomic Analysis

Mass spectrometry-based urinary proteomics is one of the most attractive strategies to discover proteins for diagnosis, prognosis, monitoring, or prediction of therapeutic responses of urological diseases involving the kidney, prostate, and bladder; however, interfering compounds found in urine necessitate sample preparation strategies that are currently not suitable for urinary proteomics in the clinical setting. Herein, we describe the C4-tip method, comprising a simple, automated strategy utilizing a reverse-phase resin tip-based format and "on-tip" digestion to examine the urine proteome. We first determined the optimal conditions for protein isolation and protease digestion on the C4-tip using the standard protein bovine fetuin. Next, we applied the C4-tip method to urinary proteomics, identifying a total of 813 protein groups using LC-MS/MS, with identified proteins from the C4-tip method displaying a similar distribution of gene ontology (GO) cellular component assignments compared to identified proteins from an ultrafiltration preparation method. Finally, we assessed the reproducibility of the C4-tip method, revealing a high Spearman correlation R-value for shared proteins identified across all tips. Together, we have shown the C4-tip method to be a simple, robust method for high-throughput analysis of the urinary proteome by mass spectrometry in the clinical setting.