99mTc-DTPA volume of distribution, half-life and glomerular filtration rate in normal adults

Multiparametric MRI based assessment of kidney injury in a mouse model of ischemia reperfusion injury

Kidney diseases pose a global healthcare burden, with millions requiring renal replacement therapy. Ischemia/reperfusion injury (IRI) is a common pathology of acute kidney injury, causing hypoxia and subsequent inflammation-induced kidney damage. Accurate detection of acute kidney injury due to IRI is crucial for timely intervention. We used longitudinal, multi-parametric magnetic resonance imaging (MRI) employing arterial spin labelling (ASL), diffusion weighted imaging (DWI), and dynamic contrast enhanced (DCE)-MRI to assess IRI induced changes in both the injured and healthy contralateral kidney, in a unilateral IRI mouse model (n = 9). Multi-parametric MRI demonstrated significant differences in kidney volume (p = 0.001), blood flow (p = 0.002), filtration coefficient (p = 0.038), glomerular filtration rate (p = 0.005) and apparent diffusion coefficient (p = 0.048) between the injured kidney and contralateral kidney on day 1 post-IRI surgery. Identification of the injured kidney using principal component analysis including most of the imaging parameters demonstrated an area under the curve (AUC) of 0.97. These results point to the utility of multi-parametric MRI in early detection of IRI-induced kidney damage suggesting that the combination of various MRI parameters may be suitable for monitoring the extent of injury in this model.

Has the time come for age-adapted glomerular filtration rate criteria to define chronic kidney disease: how soon is now?

PURPOSE OF REVIEW

The conventional definition of chronic kidney disease (CKD) primarily relies on the identification of albuminuria or a decline in estimated glomerular filtration rate (eGFR). For many years, a straightforward eGFR threshold of <60 ml/min/1.73 m 2 has been widely adopted as the standard for defining CKD. Nonetheless, this criterion fails to consider the natural aging process of the kidney, and this oversight may affect the accurate diagnosis of kidney disease particularly at the extremes of age.

RECENT FINDINGS

The fixed eGFR threshold of <60 ml/min/1.73 m 2 for defining CKD misses crucial opportunities for risk prevention. Studies have revealed that the eGFR threshold at which the risks for adverse long-term health outcomes such as mortality, cardiovascular events, and kidney failure begin to rise varies substantially by age. Specifically, this threshold is lower for the elderly and higher for young adults. Consequently, this results in the over-diagnosis of kidney disease in the elderly and the under-diagnosis of kidney disease in young adults.

SUMMARY

To address these limitations of the current CKD definition, we discuss a number of proposed age-adapted eGFR criteria and weigh their pros and cons against the current, simple, and universally accepted approach.

Functional and histologic imaging of urinary bladder wall after exposure to psychological stress and protamine sulfate

To quantify the urinary bladder wall T1 relaxation time (T1) before and after the instillation contrast mixture in rats previously subjected to water avoidance stress (WAS) and/or acute exposure to protamine sulfate (PS). Female Wistar rats were randomized to receive either sham (control) or 1 h of WAS for ten consecutive days before the evaluation of nocturnal urination pattern in metabolic cages. T1 mapping of urinary bladder wall at 9.4 T was performed pre- and post- instillation of 4 mM Gadobutrol in a mixture with 5 mM Ferumoxytol. Subsequently, either T1 mapping was repeated after brief intravesical PS exposure or the animals were sacrificed for histology and analyzing the mucosal levels of mRNA. Compared to the control group, WAS exposure decreased the single void urine volume and shortened the post-contrast T1 relaxation time of mucosa- used to compute relatively higher ingress of instilled Gadobutrol. Compromised permeability in WAS group was corroborated by the urothelial denudation, edema and ZO-1 downregulation. PS exposure doubled the baseline ingress of Gadobutrol in both groups. These findings confirm that psychological stress compromises the paracellular permeability of bladder mucosa and its non-invasive assay with MRI was validated by PS exposure.

Technetium-99m-MAG3 and technetium-99m-DTPA: Renal clearance measured by the constant infusion technique - Old news?

BACKGROUND

Accurate, precise and straightforward methods for measuring glomerular filtration rate (GFR) and/or renal plasma flow (RPF) are still in demand today. The time-consuming constant infusion technique (CIT) is the gold standard and preferred for research, whereas the simple, but less precise, single injection technique (SIT) is used in clinical settings. This study investigated the use of ^99m Tc-DTPA and ^99m Tc-MAG₃ by CIT as a measure of renal function. We developed and evaluated a model to balance the primer dose and infusion rate in an attempt to obtain plasma steady state as quickly as possible.

METHODS

14 healthy subjects received ^99m Tc-DTPA and 6 hypertensive patients received ^99m Tc-MAG₃ in a standardized protocol. All participants had an eGFR above 60 ml/min and none had fluid retention. An intravenous primer injection of the relevant tracer was followed by a sustained infusion over 4.5 h with the same radiopharmaceutical. Blood and urine samples were collected at fixed intervals.

RESULTS

^99m Tc-DTPA clearance reached steady state after 210 min (plasma clearance 78 ± 18 ml/min, urine clearance 110 ± 28 ml/min), whereas ^99m Tc-MAG₃  clearance achieved steady state after 150 min (plasma clearance 212 ± 56 ml/min, urine clearance 233 ± 59 ml/min).

CONCLUSION

Constant infusion technique with fixed primer and infusion rate using ^99m Tc-MAG₃ is feasible for research purposes. The longer time for reaching plasma steady state using ^99m Tc-DTPA makes CIT with this tracer less optimal. If the primer/sustained balance can be optimized, for example using a priori SIT information, ^99m Tc-DTPA as tracer for CIT may also be feasible.

CKD: A Call for an Age-Adapted Definition

Current criteria for the diagnosis of CKD in adults include persistent signs of kidney damage, such as increased urine albumin-to-creatinine ratio or a GFR below the threshold of 60 ml/min per 1.73 m2 This threshold has important caveats because it does not separate kidney disease from kidney aging, and therefore does not hold for all ages. In an extensive review of the literature, we found that GFR declines with healthy aging without any overt signs of compensation (such as elevated single-nephron GFR) or kidney damage. Older living kidney donors, who are carefully selected based on good health, have a lower predonation GFR compared with younger donors. Furthermore, the results from the large meta-analyses conducted by the CKD Prognosis Consortium and from numerous other studies indicate that the GFR threshold above which the risk of mortality is increased is not consistent across all ages. Among younger persons, mortality is increased at GFR <75 ml/min per 1.73 m2, whereas in elderly people it is increased at levels <45 ml/min per 1.73 m2 Therefore, we suggest that amending the CKD definition to include age-specific thresholds for GFR. The implications of an updated definition are far reaching. Having fewer healthy elderly individuals diagnosed with CKD could help reduce inappropriate care and its associated adverse effects. Global prevalence estimates for CKD would be substantially reduced. Also, using an age-specific threshold for younger persons might lead to earlier identification of CKD onset for such individuals, at a point when progressive kidney damage may still be preventable.

Measuring extracellular volume fraction by MRI: First verification of values given by clinical sequences

Purpose

To verify MR measurements of myocardial extracellular volume fraction (ECV) based on clinically applicable T1‐mapping sequences against ECV measurements by radioisotope tracer in pigs and to relate the results to those obtained in volunteers.

Methods

Between May 2016 and March 2017, 8 volunteers (25 ± 4 years, 3 female) and 8 pigs (4 female) underwent ECV assessment with SASHA, MOLLI5(3b)3, MOLLI5(3s)3, and MOLLI5s(3s)3s. Myocardial ECV was measured independently in pigs using a radioisotope tracer method.

Results

In pigs, ECV in normal myocardium was not different between radioisotope (average ± standard deviation; 19 ± 2%) and SASHA (21 ± 2%; P = 0.086). ECV was higher by MOLLI5(3b)3 (26 ± 2%), MOLLI5(3s)3 (25 ± 2%), and MOLLI5s(3s)3s (25 ± 2%) compared with SASHA or radioisotope (P ≤ 0.001 for all). ECV in volunteers was higher by MOLLI5(3b)3 (26 ± 3%) and MOLLI5(3s)3 (26 ± 3%) than by SASHA (22 ± 3%; P = 0.022 and P = 0.033). No difference was found between MOLLI5s(3s)3s (25 ± 3%) and SASHA (P = 0.225). Native T1 of blood and myocardium as well as postcontrast T1 of myocardium was consistently lower using MOLLI compared with SASHA. ECV increased over time as measured by MOLLI5(3b)3 and MOLLI5(3s)3 for pigs (0.08% and 0.07%/min; P = 0.004 and P = 0.013) and by MOLLI5s(3s)3s for volunteers (0.07%/min; P = 0.032) but did not increase as measured by SASHA.

Conclusion

Clinically available MOLLI and SASHA techniques can be used to accurately estimate ECV in normal myocardium where MOLLI‐sequences show minor overestimation driven by underestimation of postcontrast T1 when compared with SASHA. The timing of imaging after contrast administration affected the measurement of ECV using some variants of the MOLLI sequence.

An electronic technetium-99m-diethylenetriaminepentaacetic acid glomerular filtration rate spreadsheet with novel embedded quality assurance features

Supplemental Digital Content is available in the text.

Background

Critical clinical decisions are made on the basis of the glomerular filtration rate (GFR) measured using technetium-99m-diethylenetriaminepentaacetic acid (DTPA) administration, followed by multiple time-point plasma sampling. As GFR studies rely on few data points and produce a single result, they are prone to technical errors that may remain inconspicuous.

Objective

We describe a data analysis worksheet that provides real-time quality control (QC) indicators and evaluate our initial clinical experience.

Methods

Two hundred and forty-six consecutive GFR studies carried out at our clinics were included. Our protocol used plasma samples at 2, 3, and 4 h after injection of technetium-99m-DTPA. Duplicate plasma samples, background samples, and aliquots of an activity dilution standard were counted. Times were logged for injection and dilution standard preparation, blood sampling, and counting. Data were entered into a custom GFR analysis spreadsheet that flagged QC in real time at warning and error levels, including QC of the expected ratio between dilution standard counts–activity ratio (CARs) measurements, which was newly introduced to our clinic. The prevalence of QC events was analyzed in three phases: baseline, training, and evaluation (n=31, 69, and 146, respectively).

Results

From the baseline and training phases (n=100), CAR reference values were determined for each of two sites. In the absence of the CAR QC indicator, errors were present in 5/31 (16%) examinations, but with QC indication decreased to 7/146 (5%) (P<0.05), suggesting that the real-time QC information guided the technologists to ensure proper standard preparation and sample handling, as intended. Improvements in other QC measures were also noted, resulting in an overall error rate reduction from 23 to 8%.

Conclusion

Real-time analysis of redundant information as a component of the GFR worksheet ensures quality results, but training of technologists and interpreting physicians is essential for optimal utilization of these QC indicators.

Terminalia arjuna bark extract improves diuresis and attenuates acute hypobaric hypoxia induced cerebral vascular leakage

ETHNOPHARMACOLOGICAL RELEVANCE

Terminalia arjuna (Roxb. ex DC.) Wight & Arn. (T. arjuna) has been widely used in the traditional ayurvedic system of medicine as a cardioprotectant and for acute and chronic renal diseases supporting its ethnopharmacological use.

AIM OF THE STUDY

The present study aimed at evaluating the diuretic action of an alcoholic extract of T. arjuna and its possible use as a prophylactic to prevent vascular leakage during acute mountain sickness at high altitude.

MATERIALS AND METHODS

Rats were exposed to hypobaric hypoxia simulated to an altitude of 27,000 ft. in a decompression chamber for 12h. T. arjuna bark extract was administered at a single dose of 150 mg/kg (p.o.) to male Sprague Dawley rats (200 ± 20 g) 30 min prior to exposure. Total urine volume was measured during exposure to hypobaric hypoxia. The animals were then investigated for cerebral vascular leakage and serum concentration of sodium, potassium, renin, angiotensin-II, aldosterone and atrial natriuretic peptide (ANP).

RESULTS

T. arjuna ameliorated acute hypobaric hypoxia induced decrease in glomerular filtration rate (p<0.5), increased total urine output (p<0.5) and prevented cerebral vascular leakage in hypoxic rats. T. arjuna treated animals also showed decrease in serum levels of renin (p<0.001) and angiotensin-II (p<0.5) as compared to placebo treated animals. Administration of T. arjuna attenuated acute hypobaric hypoxia induced oxidative stress, improved aldosterone levels and altered electrolyte balance in animals through ANP dependent mechanism.

CONCLUSION

Results of the present study indicate towards diuretic potential of hydro-alcoholic extract of T. arjuna bark and provide evidence for its novel application as a prophylactic to attenuate acute hypobaric hypoxia induced cerebral vascular leakage through ANP mediated modulation of renin-angiotensin-aldosterone system.

Elevated baseline glomerular filtration rate (GFR) is independently associated with a more rapid decline in renal function of patients with type 1 diabetes

AIMS

Renal hyperfiltration is observed prior to the development of diabetic kidney disease (DKD) in patients with type 1 diabetes (T1DM); however its significance remains uncertain. Longitudinal data were used to investigate the association between measured baseline glomerular filtration rate (GFR) and renal function decline in patients with T1DM.

METHODS

This study included 142 adult patients with T1DM and ≥2 measurements of glomerular filtration rate (mGFR; determined by diethylene-triamine-penta-acetic acid plasma clearance). Median follow up was 19 years. Patients were stratified by baseline mGFR quartile. The relationship between baseline mGFR and rate of renal function decline was assessed using random-effect generalized least squares regression, adjusted for age, duration of diabetes, HbA1c, blood pressure, renin-angiotensin-aldosterone system inhibitor therapy, LDL and BMI.

RESULTS

The average rates of decline in renal function for the 2nd (baseline mGFR: 96.4-112.6 ml min-(1) 1.73 m-(2)), 3(rd) (baseline mGFR: 112.6-125.5 ml min- (1) 1.73 m-(2)) and 4th quartiles (baseline mGFR >125.5 ml min-(1) 1.73 m-(2)) were significantly faster than the first quartile (baseline mGFR: 60.9-96.4 ml min-(1) 1.73 m-(2)). In further detail, the average rates of decline in the 2nd (rate of decline 1.25 ml min- (1) 1.73 m-(2) per year, 95% CI: 0.97; 1.52, p=0.008), 3rd (rate of decline 1.35 ml min-(1) 1.73 m-(2) per year, 95% CI: 1.08; 1.62, p= 0.001) and 4th quartiles (rate of decline 1.6 ml min-(1) 1.73 m-(2) per year, 95% CI: 1.34, 1.88, <0.0001) were significantly faster when compared to the first quartile (rate of decline 0.67 ml min-(1) 1.73 m-(2) per year, 95% CI: 0.37; 0.96). Sub-analysis of quartile 4 revealed higher HbA1c measurements throughout follow-up in those with rapid mGFR decline (>3.0 ml min(-1)1.73 m(-2)/year).

CONCLUSIONS

In patients with T1DM, higher baseline mGFR is associate ed with more rapid mGFR decline. Patients with high baseline mGFR who developed rapid mGFR decline had higher HbA1c measurements throughout the study. These findings are consistent with the concept that poor glycaemic control over time may be a determining factor for the rapid renal function decline observed in some hyperfiltering patients.