The association of urine osmolality with decreased kidney function and/or albuminuria in the United States

Clinical Assessment of Fluid Status in Adults With Acute Kidney Injury: A Scoping Review

BACKGROUND

Acute kidney injury refers to sudden, potentially reversible, reduction in kidney function. Hypovolaemia is commonly the major risk factor. When acute kidney injury is established, fluid can accumulate leading to fluid overload. Undertaking a rigorous fluid assessment is vital in the management of a patient in hospital with acute kidney injury, as insufficient or excessive fluid can lead to increased morbidity and mortality.

OBJECTIVES

The aim of this scoping review is to identify which clinical assessments are useful when undertaking fluid assessment in a patient with acute kidney injury, and to identify signs and symptoms of fluid overload or dehydration in patients in hospital with acute kidney injury.

DESIGN

The JBI methodology for scoping reviews was followed and reported using the PRISMA-ScR checklist. PubMed, CINAHL Plus and SCOPUS were searched for research papers relating to the signs and symptoms or fluid assessments in patients with acute kidney injury.

RESULTS

Fifteen research papers were identified with four key areas being: Fluid balance/urine output and weight; early warning scores; clinical signs and symptoms; holistic assessment. The primary studies included in this scoping review have shown that hypovolaemia may be indicated by low blood pressure, orthostatic hypotension, low Mean Arterial Pressure, elevated heart rate, prolonged capillary refill time on the sternum (> 4.5 s) and subjectively reported cold peripheries. With clinical symptoms including dry mouth, increased thirst and dry skin. Accurate documentation of urine output and fluid balance is crucial in determining fluid status.

CONCLUSION

The assessment of fluid should be holistic and include history taking, diagnosis, blood tests and associated clinical signs and symptoms.

The role of the clinical laboratory in diagnosing hyponatremia disorders

In clinical medicine, hyponatremia is highly prevalent and frequently misdiagnosed, leading to substantial mismanagement and iatrogenic morbidity. Its differential diagnosis includes numerous diseases with diverse etiologies, making accurate assessment challenging. Despite extensive literature and guidelines on hyponatremia, most patients do not receive adequate evaluation due to the limitations of diagnostic algorithms, which rely on low-value clinical signs and are unable to identify concurrent conditions. In this review, we examine the range of laboratory tests available for hyponatremia assessment. Understanding renal mechanisms of solute and water exchange (e.g., fractional excretion) is essential for selecting appropriate tests and interpreting their diagnostic value. Additionally, detailed electrolyte and acid-base assessments remain critical for establishing a definitive diagnosis. We comprehensively discuss the selection of laboratory tests for specific differential diagnoses of hyponatremia. Importantly, in cases of acute hyponatremia, rapid correction should take precedence over a complete diagnostic workup. Ultimately, a thorough understanding of laboratory evaluation is crucial for accurately diagnosing hyponatremia. This paper critically reviews the available literature and explores relevant diseases in the context of associated laboratory parameters.

Disentangling the phenotypic patterns of hypertension and chronic hypotension

OBJECTIVE

2017 blood pressure (BP) categories focus on cardiac risk. We hypothesize that studying the balance between mechanisms that increase or decrease BP across the medical phenome will lead to new insights. We devised a classifier that uses BP measures to assign individuals to mutually exclusive categories centered in the upper (Htn), lower (Hotn) and middle (Naf) zones of the BP spectrum; and examined the epidemiologic and phenotypic patterns of these BP-categories.

METHODS

We classified a cohort of 832,560 deidentified electronic health records by BP-category; compared the frequency of BP-categories and four subtypes of Htn and Hotn by sex and age-decade; visualized the distributions of systolic, diastolic, mean arterial and pulse pressures stratified by BP-category; and ran Phenome-wide Association Studies (PheWAS) for Htn and Hotn. We paired knowledgebases for hypertension and hypotension and computed aggregate knowledgebase status (KB-status) indicating known associations. We assessed alignment of PheWAS results with KB-status for phecodes in the knowledgebase, and paired PheWAS correlations with KB-status to surface phenotypic patterns.

RESULTS

BP-categories represent distinct distributions within the multimodal distributions of systolic and diastolic pressure. They are centered in the upper, lower, and middle zones of mean arterial pressure and provide a different signal than pulse pressure. For phecodes in the knowledgebase, 85% of positive correlations align with KB-status. Phenotypic patterns for Htn and Hotn overlap for several phecodes and are separate for others. Our analysis suggests five candidates for hypothesis testing research, two where the prevalence of the association with Htn or Hotn may be under appreciated, three where mechanisms that increase and decrease blood pressure may be affecting one another's expression.

CONCLUSION

PairedPheWAS methods may open a phenome-wide path to disentangling hypertension and chronic hypotension. Our classifier provides a starting point for assigning individuals to BP-categories representing the upper, lower, and middle zones of the BP spectrum. 4.7 % of individuals matching 2017 BP categories for normal, elevated BP or isolated hypertension, have diastolic pressure < 60. Research is needed to fine-tune the classifier, provide external validation, evaluate the clinical significance of diastolic pressure < 60, and test the candidate hypotheses.

Is mild dehydration a risk for progression of childhood chronic kidney disease?

Children with chronic kidney disease (CKD) can have an inherent vulnerability to dehydration. Younger children are unable to freely access water, and CKD aetiology and stage can associate with reduced kidney concentrating capacity, which can also impact risk. This article aims to review the risk factors and consequences of mild dehydration and underhydration in CKD, with a particular focus on evidence for risk of CKD progression. We discuss that assessment of dehydration in the CKD population is more challenging than in the healthy population, thus complicating the definition of adequate hydration and clinical research in this field. We review pathophysiologic studies that suggest mild dehydration and underhydration may cause hyperfiltration injury and impact renal function, with arginine vasopressin as a key mediator. Randomised controlled trials in adults have not shown an impact of improved hydration in CKD outcomes, but more vulnerable populations with baseline low fluid intake or poor kidney concentrating capacity need to be studied. There is little published data on the frequency of dehydration, and risk of complications, acute or chronic, in children with CKD. Despite conflicting evidence and the need for more research, we propose that paediatric CKD management should routinely include an assessment of individual dehydration risk along with a treatment plan, and we provide a framework that could be used in outpatient settings.

Excess microtubule and F-actin formation mediates shortening and loss of primary cilia in response to a hyperosmotic milieu

The primary cilium is a small organelle protruding from the cell surface that receives signals from the extracellular milieu. Although dozens of studies have reported that several genetic factors can impair the structure of primary cilia, evidence for environmental stimuli affecting primary cilia structures is limited. Here, we investigated an extracellular stress that affected primary cilia morphology and its underlying mechanisms. Hyperosmotic shock induced reversible shortening and disassembly of the primary cilia of murine intramedullary collecting duct cells. The shortening of primary cilia caused by hyperosmotic shock followed delocalization of the pericentriolar material (PCM). Excessive microtubule and F-actin formation in the cytoplasm coincided with the hyperosmotic shock-induced changes to primary cilia and the PCM. Treatment with a microtubule-disrupting agent, nocodazole, partially prevented the hyperosmotic shock-induced disassembly of primary cilia and almost completely prevented delocalization of the PCM. An actin polymerization inhibitor, latrunculin A, also partially prevented the hyperosmotic shock-induced shortening and disassembly of primary cilia and almost completely prevented delocalization of the PCM. We demonstrate that hyperosmotic shock induces reversible morphological changes in primary cilia and the PCM in a manner dependent on excessive formation of microtubule and F-actin.

Detection of low urine output by measuring urinary biomarkers

BACKGROUND

Urine output < 1 L per 24 h is a clinical warning sign that requires attention from hospital staff, who should determine whether the low flow is due to low habitual intake of water or disease-induced dehydration. The incidence of this condition is unclear.

METHODS

A cohort of 20 healthy volunteers (mean age 42 years, range 23-62 years) recorded their food and water intakes daily for 8 days. They also collected and measured all urine and delivered first morning urine samples for analysis of osmolality and creatinine. Optimal cutoffs for these biomarkers to indicate urine output of < 1 L or 15 mL/kg during the preceding 24 h were applied with and without correction for age to cross-sectional data from 1,316 subjects in various clinical settings, including healthy volunteers, preoperative patients, patients seeking acute care at a hospital, and patients receiving institutional geriatric care.

RESULTS

The urine output amounted to < 1 L during 22 of the 159 evaluable study days and was indicated by urine osmolality > 760 mosmol/kg or urine creatinine > 13 mmol/L, which had sensitivity and specificity of approximately 80%. Days with urine output < 1 L were associated with significantly less intake of both water (-41%) and calories (-22%) compared to other days. Application of age-corrected biomarker cutoffs to the 1,316 subjects showed a stronger dependency of low urine output on age than the clinical setting, occurring in 44% of the 72 participants aged 15-30 years and 18% of the 62 patients aged 90-104 years.

CONCLUSION

Biomarkers measured in morning urine of young and middle-aged volunteers indicated urine output of < 1 L with good precision, but the cutoffs should be validated in older age groups to yield reliable results.

TRIAL REGISTRATIONS

ISRCTN12215472 at http://www.isrctn.com ; NCT01458678 at ClinicalTrials.gov, and ChiCTR-TNRC-14,004,479 at the chictr.org/en.

Concentrated urine, low urine flow, and postoperative elevation of plasma creatinine: A retrospective analysis of pooled data

Elevations of plasma creatinine are common after major surgery, but their pathophysiology is poorly understood. To identify possible contributing mechanisms, we pooled data from eight prospective studies performed in four different countries to study circumstances during which elevation of plasma creatinine occurs. We included 642 patients undergoing mixed major surgeries, mostly open gastrointestinal. Plasma and urinary creatinine and a composite index for renal fluid conservation (Fluid Retention Index, FRI) were measured just before surgery and on the first postoperative morning. Urine flow was measured during the surgery. The results show that patients with a postoperative increase in plasma creatinine by >25% had a high urinary creatinine concentration (11.0±5.9 vs. 8.3±5.6 mmol/L; P< 0001) and higher FRI value (3.2±1.0 vs. 2.9±1.1; P< 0.04) already before surgery was initiated. Progressive increase of plasma creatinine was associated with a gradually lower urine flow and larger blood loss during the surgery (Kruskal-Wallis test, P< 0.001). The patients with an elevation > 25% also showed higher creatinine and a higher FRI value on the first postoperative morning (P< 0.001). Elevations to > 50% of baseline were associated with slightly lower mean arterial pressure (73 ± 10 vs. 80 ± 12 mmHg; P< 0.005). We conclude that elevation of plasma creatinine in the perioperative period was associated with low urine flow and greater blood loss during surgery and with concentrated urine both before and after the surgery. Renal water conservation-related mechanisms seem to contribute to the development of increased plasma creatinine after surgery.