Structural Equation Modelling to Identify Psychometric Determinants of Medication Adherence in a Survey of Kidney Dialysis Patients

Purpose

Medication non-adherence in dialysis patients is associated with increased mortality and higher healthcare costs. We assessed whether medication adherence is influenced by specific psychometric constructs measuring beliefs about the necessity for medication and concerns about them. We also tested whether medication knowledge, health literacy, and illness perceptions influenced this relationship.

Patients and Methods

This study is based on data from a cross-sectional in-person questionnaire, administered to a random sample of all adult dialysis patients at a teaching hospital. The main outcome was self-assessed medication adherence (8-Item Morisky Medication Adherence Scale). The predictors were: concerns about medications and necessity for medication (Beliefs About Medication Questionnaire); health literacy; medication knowledge (Medication Knowledge Evaluation Tool); cognitive, emotional, and comprehensibility Illness perceptions (Brief Illness Perception Questionnaire). Path analysis was performed using structural equations in both covariance and variance-based models.

Results

Necessity for medication increased (standardized path coefficient [β] 0.30 [95% CI 0.05, 0.54]) and concerns about medication decreased (standardized β -0.33 [-0.57, -0.09]) medication adherence, explaining most of the variance in outcome (r2=0.95). Medication knowledge and cognitive illness perceptions had no effects on medication adherence, either directly or indirectly. Higher health literacy, greater illness comprehension, and a more positive emotional view of their illness had medium-to-large sized effects in increasing medication adherence. These were indirect rather and direct effects mediated by decreases in concerns about medications (standardized β respectively -0.40 [-0.63,-0.16], -0.60 [-0.85, -0.34], -0.33 [-0.52, -0.13]).

Conclusion

Interventions that reduce patients' concerns about their medications are likely to improve adherence, rather than interventions that increase patients' perceived necessity for medication. Improving patients' general health literacy and facilitating a better understanding and more positive perception of the illness can probably achieve this. Our study is potentially limited by a lack of generalizability outside of the population and setting in which it was conducted.

In Primary Aldosteronism Acute Potassium Chloride Supplementation Suppresses Abundance and Phosphorylation of the Sodium-Chloride Cotransporter

Background

Elevated abundance of sodium-chloride cotransporter (NCC) and phosphorylated NCC (pNCC) are potential markers of primary aldosteronism (PA), but these effects may be driven by hypokalemia.

Methods

We measured plasma potassium in patients with PA. If potassium was <4.0 mmol/L, patients were given sufficient oral potassium chloride (KCl) over 24 hours to achieve as close to 4.0 mmol/L as possible. Clinical chemistries were assessed, and urinary extracellular vesicles (uEVs) were examined to investigate effects on NCC.

Results

Among 21 patients with PA who received a median total dose of 6.0 g (2.4-16.8 g) of KCl, increases were observed in plasma potassium (from 3.4 to 4.0 mmol/L; P<0.001), aldosterone (from 305 to 558 pmol/L; P=0.01), and renin (from 1.2 to 2.5 mIU/L; P<0.001), whereas decreases were detected in uEV levels of NCC (median fold change_(post/basal) [FC]=0.71 [0.09-1.99]; P=0.02), pT60-NCC (FC=0.84 [0.06-1.66]; P=0.05), and pT55/60-NCC (FC=0.67 [0.08-2.42]; P=0.02). By contrast, in 10 patients with PA who did not receive KCl, there were no apparent changes in plasma potassium, NCC abundance, and phosphorylation status, but increases were observed in plasma aldosterone (from 178 to 418 pmol/L; P=0.006) and renin (from 2.0 to 3.0 mU/L; P=0.009). Plasma potassium correlated inversely with uEV levels of NCC (R ²=0.11; P=0.01), pT60-NCC (R ²=0.11; P=0.01), and pT55/60-NCC (R ²=0.11; P=0.01).

Conclusions

Acute oral KCl loading replenished plasma potassium in patients with PA and suppressed NCC abundance and phosphorylation, despite a significant rise in plasma aldosterone. This supports the view that potassium supplementation in humans with PA overrides the aldosterone stimulatory effect on NCC. The increased plasma aldosterone in patients with PA without KCl supplementation may be due to aldosterone response to posture challenge.

Acute Intravenous NaCl and Volume Expansion Reduces Sodium-Chloride Cotransporter Abundance and Phosphorylation in Urinary Extracellular Vesicles

Background

Sodium chloride (NaCl) loading and volume expansion suppress the renin-angiotensin-aldosterone system to reduce renal tubular reabsorption of NaCl and water, but effects on the sodium-chloride cotransporter (NCC) and relevant renal transmembrane proteins that are responsible for this modulation in humans are less well investigated.

Methods

We used urinary extracellular vesicles (uEVs) as an indirect readout to assess renal transmembrane proteins involved in NaCl and water homeostasis in 44 patients with hypertension who had repeatedly raised aldosterone/renin ratios undergoing infusion of 2 L of 0.9% saline over 4 hours.

Results

When measured by mass spectrometry in 13 patients, significant decreases were observed in NCC (median fold change [FC]=0.70); pendrin (FC=0.84); AQP2 (FC=0.62); and uEV markers, including ALIX (FC=0.65) and TSG101 (FC=0.66). Immunoblotting reproduced the reduction in NCC (FC=0.54), AQP2 (FC=0.42), ALIX (FC=0.52), and TSG101 (FC=0.55) in the remaining 31 patients, and demonstrated a significant decrease in phosphorylated NCC (pNCC; FC=0.49). However, after correction for ALIX, the reductions in NCC (FC=0.90) and pNCC (FC=1.00) were no longer apparent, whereas the significant decrease in AQP2 persisted (FC=0.62).

Conclusion

We conclude that (1) decreases in NCC and pNCC, induced by acute NaCl loading and volume expansion, may be due to diluted post-test urines; (2) the lack of change of NCC and pNCC when corrected for ALIX, despite a fall in plasma aldosterone, may be due to the lack of change in plasma K⁺; and (3) the decrease in AQP2 may be due to a decrease in vasopressin in response to volume expansion.

Using human urinary extracellular vesicles to study physiological and pathophysiological states and regulation of the sodium chloride cotransporter

The thiazide-sensitive sodium chloride cotransporter (NCC), expressed in the renal distal convoluted tubule, plays a major role in Na⁺, Cl^- and K⁺ homeostasis and blood pressure as exemplified by the symptoms of patients with non-functional NCC and Gitelman syndrome. NCC activity is modulated by a variety of hormones, but is also influenced by the extracellular K⁺ concentration. The putative "renal-K⁺ switch" mechanism is a relatively cohesive model that links dietary K⁺ intake to NCC activity, and may offer new targets for blood pressure control. However, a remaining hurdle for full acceptance of this model is the lack of human data to confirm molecular findings from animal models. Extracellular vesicles (EVs) have attracted attention from the scientific community due to their potential roles in intercellular communication, disease pathogenesis, drug delivery and as possible reservoirs of biomarkers. Urinary EVs (uEVs) are an excellent sample source for the study of physiology and pathology of renal, urothelial and prostate tissues, but the diverse origins of uEVs and their dynamic molecular composition present both methodological and data interpretation challenges. This review provides a brief overview of the state-of-the-art, challenges and knowledge gaps in current uEV-based analyses, with a focus on the application of uEVs to study the "renal-K⁺ switch" and NCC regulation. We also provide recommendations regarding biospecimen handling, processing and reporting requirements to improve experimental reproducibility and interoperability towards the realisation of the potential of uEV-derived biomarkers in hypertension and clinical practice.

Haemodialysis withdrawal in Australia and New Zealand: a binational registry study

BACKGROUND

Withdrawal from dialysis is an increasingly common cause of death in patients with end-stage kidney disease (ESKD). As most published reports of dialysis withdrawal have been outside the Oceania region, the aims of this study were to determine the frequency, temporal pattern and predictors of dialysis withdrawal in Australian and New Zealand patients receiving chronic haemodialysis.

METHODS

This study included all people with ESKD in Australia and New Zealand who commenced chronic haemodialysis between 1 January 1997 and 31 December 2016, using data from the Australia and New Zealand Dialysis and Transplant (ANZDATA) Registry. Competing risk regression models were used to identify predictors of dialysis withdrawal mortality, using non-withdrawal cause of death as the competing risk event.

RESULTS

Among 40 447 people receiving chronic haemodialysis (median age 62 years, 61% male, 9% Indigenous), dialysis withdrawal mortality rates increased from 1.02 per 100 patient-years (11% of all deaths) during the period 1997-2000 to 2.20 per 100 patient-years (32% of all deaths) during 2013-16 (P < 0.001). Variables that were significantly associated with a higher likelihood of haemodialysis withdrawal were older age {≥70 years subdistribution hazard ratio [SHR] 1.77 [95% confidence interval (CI) 1.66-1.89]; reference 60-70 years}, female sex [SHR 1.14 (95% CI 1.09-1.21)], white race [Asian SHR 0.56 (95% CI 0.49-0.65), Aboriginal and Torres Strait Islander SHR 0.83 (95% CI 0.74-0.93), Pacific Islander SHR 0.47 (95% CI 0.39-0.68), reference white race], coronary artery disease [SHR 1.18 (95% CI 1.11-1.25)], cerebrovascular disease [SHR 1.15 (95% CI 1.08-1.23)], chronic lung disease [SHR 1.13 (95% CI 1.06-1.21)] and more recent era [2013-16 SHR 3.96 (95% CI 3.56-4.48); reference 1997-2000].

CONCLUSIONS

Death due to haemodialysis withdrawal has become increasingly common in Australia and New Zealand over time. Predictors of haemodialysis withdrawal include older age, female sex, white race and haemodialysis commencement in a more recent era.

Large uremic toxins: an unsolved problem in end-stage kidney disease

Patients with end-stage kidney disease (ESKD) on maintenance hemodialysis are subject to a high burden of inflammation and cardiovascular disease, driven at least in part by retention of uremic solutes. Existing dialysis technologies using high-flux membranes offer limited clearance of solutes >15 kDa. New approaches to improve the removal of large uremic toxins include the novel medium cut-off dialysis membranes with pores larger than those in high-flux membranes. These new membranes provide the potential to improve the clearance of large middle molecules up to 50 kDa. In this review, we discuss 18 uremic toxins with molecular weights between 15 and 60 kDa that are retained in ESKD, for which there is evidence of a link to inflammation and/or cardiovascular disease. These include inflammatory proteins, cytokines, adipokines and other signaling proteins. Improved clearance of this group of difficult to remove molecules has the potential to lead to improved outcomes in dialysis patients by reducing the burden of cardiovascular disease, which now needs to be assessed in robust clinical trials.

Outcomes and practice patterns with hemodiafiltration in Shanghai: a longitudinal cohort study

BACKGROUND

Globally, there is increased clinical interest and uptake of hemodiafiltration (HDF) for increased removal of uremic toxins. To date, there has been no epidemiological analysis of HDF in China. We present HDF practice patterns and associated mortality risk in Shanghai.

METHODS

This is an observational, prospectively collected, retrospective analysis of 9351 Chinese patients initiating hemodialysis in Shanghai from 2007 to 2014. The primary exposure was hemodialysis sub-modality at inception, classified into hemodiafiltration (HDF) and hemodialysis (HD), with adjustment for concommitant hemoperfusion. The primary outcome was patient mortality. We used Cox proportional hazards regression and Fine and Gray's proportional subhazards regression, with multiple imputation of missing co-variates by the chained equation method, adjusting for demographic and clinical variables.

RESULTS

Overall, patients in the cohort were younger, with a more males, and with a lower body mass index when compared to corresponding non-Asian cohorts. Mortality rate was low although it doubled over the period of observation. HDF utilization increased from 7% of patients in 2007 to 42% of patients in 2014. The majority of patients received HDF once a week. The adjusted hazard ratio of death (95% confidence intervals) for HDF versus HD was 0.85 (0.71-1.03), and corresponding sub-hazard ratio 0.86 (0.71-1.03). There was strong effect modification by age. In those aged 40-60 years, the hazard ratio (95% confidence intervals) was 0.65 (0.45-0.94), and sub-hazard ratio also 0.65 (0.45-0.95).

CONCLUSIONS

Our study has certain limitations resulting from the limited number of co-variates available for modelling, missing data for some co-variates, and the lack of verification of data against source documentation. Notwithstanding, there is evidence of clinical benefit from HDF in China, and potential to improve patient outcomes through the greater removal of middle and larger uremic solutes.

Treatment of primary aldosteronism is associated with a reduction in the severity of obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is known to commonly co-exist with primary aldosteronism (PA), but it is unknown if treatment of PA improves sleep apnoea parameters in these patients. We therefore aimed to determine whether specific medical or surgical treatment of PA improves OSA, as measured by the apnoea-hypopnoea index (AHI). We recruited patients undergoing diagnostic workup for PA if they had symptoms suggestive of OSA. Patients with confirmed PA underwent polysomnography (PSG) at baseline and again at least 3 months after specific treatment for PA. Of 34 patients with PA, 7 (21%) had no evidence of OSA (AHI <5), 9 (26%) had mild (AHI ⩾5 and <15), 8 (24%) moderate (AHI ⩾15 and <30) and 10 (29%) severe OSA (AHI ⩾30). Body mass index tertile, neck circumference and 24 h urinary sodium correlated with the AHI. Twenty patients had repeat PSG performed after treatment for PA (mineralocorticoid receptor antagonists in 13 with bilateral PA and adrenalectomy in 7 with unilateral PA). In this group the median (s.d.) AHI reduced from 22.5 (14.7) to 12.3 (12.1) (P=0.02). Neck circumference reduced with PA treatment (41.6 vs 41.2 cm, P=0.012). OSA is common in patients with primary aldosteronism and may improve with specific therapy for this disease. Aldosterone and sodium-mediated fluid retention in the upper airways and neck region may be a potential mechanism for this relationship.

New Advances in the Diagnostic Workup of Primary Aldosteronism

Primary aldosteronism is an important and common cause of hypertension that carries a high burden of morbidity. Outcomes, however, are excellent if diagnosed and treated appropriately. The diagnostic workup for primary aldosteronism is complex and comprises three steps: (1) screening, (2) confirmatory testing, and (3) subtype differentiation. In this review, we discuss recent advances in the diagnostic workup for primary aldosteronism. The development of accurate mass spectroscopy-based assays for measuring aldosterone will lead to improved confidence in all diagnostic aspects involving measurement of aldosterone, and accurate measurement of angiotensin II may soon advance us beyond the measurement of renin. We now have a greater understanding of hormonal influences on the aldosterone/renin ratio, which are particularly important when screening premenopausal women or those taking estrogen-containing preparations. Confirmatory testing is important, but there are limitations to the commonly used methods that have recently become more apparent, with new approaches offering a way forward. Adrenal venous sampling (AVS) is a challenging procedure but is important for deciding on treatment options. Success rates may be improved by the use of Synacthen stimulation and of rapid intraprocedural measurement of cortisol. Better understanding of AVS interpretation criteria allows improved prognostication and aids treatment decisions. The use of labeled metomidate positron emission tomography computed tomography scanning may also offer an alternative to AVS in some units. Although the diagnostic approach to patients with primary aldosteronism remains a complex multistep process in which attention to detail is important, recent advances will improve patient care and outcomes.

Does ACTH improve the diagnostic performance of adrenal vein sampling for subtyping primary aldosteronism?

OBJECTIVE

Adrenal vein sampling (AVS) is used for determining treatment options for primary aldosteronism (PA), but is a difficult procedure. Adrenocorticotropic hormone (ACTH) infusion or bolus has been reported to improve AVS success rates by increasing cortisol secretion, but effects on lateralization are controversial. We therefore assessed the effects of ACTH in regard to AVS success and lateralization in our unit, after a change in protocol to ACTH-stimulated AVS.

SETTING

AVS was performed after overnight recumbency in patients with PA confirmed by fludrocortisone suppression testing. Bilateral sequential sampling was performed before and after an intravenous bolus of 250 mcg of ACTH. Lateralization was defined as an aldosterone/cortisol ratio in one adrenal vein at least twice peripheral, combined with a contralateral adrenal ratio no higher than peripheral (contralateral suppression).

RESULTS

In 47 AVS procedures, the median adrenal/peripheral cortisol gradient increased on the left (11·6 vs 18·2 μg/100 ml, P < 0·001) and right (15·6 vs 31·5 μg/100 ml, P < 0·001) after ACTH. A total of 34 of 47 studies were diagnostic pre-ACTH (six failing because of low aldosterone levels bilaterally and seven failing to cannulate one or both sides) vs 44 of 47 (P = 0·011) studies diagnostic post-ACTH (failure to cannulate one or both sides in 3). Concordance between diagnostic studies pre- and post-ACTH was 91%, but two bilateral cases became unilateral after ACTH and one unilateral case before ACTH was bilateral afterwards.

CONCLUSIONS

ACTH improved cortisol gradients and aldosterone secretion, resulting in a reduction in the proportion of nondiagnostic studies. There was a low proportion of discordance between pre- and post-ACTH diagnoses, the significance of which is unclear.

In Primary Aldosteronism, Mineralocorticoids Influence Exosomal Sodium-Chloride Cotransporter Abundance

Distal tubular sodium retention is a potent driver of hypertension, and the thiazide-sensitive sodium-chloride cotransporter (NCC) has a key role in this process. In humans, factors regulating NCC are unclear, but in animal models, aldosterone is a potent regulator, possibly via effects on plasma potassium. We studied the effects of the mineralocorticoid fludrocortisone on the abundance of NCC and its phosphorylated form (pNCC) as well as WNK lysine deficient protein kinase 4 (WNK4) and STE20/SPS1-related, proline alanine-rich kinase (SPAK) in human urinary exosomes. We isolated exosomes from daily urine samples in 25 patients undergoing fludrocortisone suppression testing (100 μg every 6 hours for 4 days) to diagnose or exclude primary aldosteronism. Over the course of the test, NCC levels increased 3.68-fold (P<0.01) and pNCC levels increased 2.73-fold (P<0.01) relative to baseline. The ratio of pNCC/NCC dropped by 48% (P<0.01). The abundance of WNK4 increased 3.23-fold (P<0.01), but SPAK abundance did not change significantly (P=0.14). Plasma potassium concentration strongly and negatively correlated with pNCC, NCC, and WNK4 abundance (P<0.001 for all). This study shows that, in humans, mineralocorticoid administration is associated with a rapid increase in abundance of NCC and pNCC, possibly via the WNK pathway. These effects may be driven by changes in plasma potassium.

Feasibility study of colestipol as an oral phosphate binder in hemodialysis patients

BACKGROUND

Currently available calcium- and aluminium-based phosphate binders are dose limited because of potential toxicity, and newer proprietary phosphate binders are expensive. We examined phosphate-binding effects of the bile acid sequestrant colestipol, a non-proprietary drug that is in the same class as sevelamer.

METHODS

The trial was an 8 week prospective feasibility study in stable hemodialysis patients using colestipol as the only phosphate binder, preceded and followed by a washout phase of all other phosphate binders. The primary study endpoint was weekly measurements of serum phosphate. Secondary endpoints were serum calcium, lipids and coagulation status. Analyses used random effects mixed models.

RESULTS

Thirty patients were screened for participation of which 26 met criteria for treatment. At a mean dose of 8.8 g/24 h of colestipol by study end, serum phosphate dropped from 2.24 to 1.96 mmol/L (P < 0.001). Three patients required calcium supplementation. LDL cholesterol dropped from 1.75 to 1.2 mmol/L (P < 0.001). Three patients dropped out because of side effects or intolerance of the required dose.

CONCLUSION

The results support the feasibility of a larger trial to determine the efficacy of colestipol as a phosphate binder and that other non-proprietary anion-exchange resins may also warrant investigation.

Understanding barriers to optimal medication management for those requiring long-term dialysis: rationale and design for an observational study, and a quantitative description of study variables and data

Background

Rates of medication non-adherence in dialysis patients are high, and improving adherence is likely to improve outcomes. Few data are available regarding factors associated with medication adherence in dialysis patients, and these data are needed to inform effective intervention strategies.

Methods/design

This is an observational cross-sectional study of a multi-ethnic dialysis cohort from New Zealand, with the main data collection tool being an interviewer-assisted survey. A total of 100 participants were randomly sampled from a single centre, with selection stratified by ethnicity and dialysis modality (facility versus home). The main outcome measure is self-reported medication adherence using the Morisky 8-Item Medication Adherence Scale (MMAS-8). Study data include demographic, clinical, social and psychometric characteristics, the latter being constructs of health literacy, medication knowledge, beliefs about medications, and illness perceptions. Psychometric constructs were assessed through the following survey instruments; health literacy screening questions, the Medication Knowledge Evaluation Tool (Okuyan et al.), the Beliefs about Medication Questionnaire (Horne et al.), the Brief Illness Perception Questionnaire (Broadbent et al.). Using the study data, reliability analysis for internal consistency is satisfactory for the scales evaluating health literacy, medication knowledge, and beliefs about medications, with Chronbach’s α > 0.7 for all. Reliability analysis indicated poor internal consistency for scales relating to illness perceptions. MMAS-8 and all psychometric scores are normally distributed in the study data.

Discussion

This study will provide important information on the factors involved in medication non-adherence in New Zealand dialysis patients. The resulting knowledge will inform long-term initiatives to reduce medication non-adherence in dialysis patients, and help ensure that they are addressing appropriate and evidence based targets for intervention.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-015-0097-2) contains supplementary material, which is available to authorized users.

Does contralateral suppression at adrenal venous sampling predict outcome following unilateral adrenalectomy for primary aldosteronism? A retrospective study

CONTEXT

In primary aldosteronism (PA), adrenal vein sampling (AVS) distinguishes unilateral and bilateral disease by comparison of aldosterone/cortisol (A/F) ratios. There is controversy about the criteria for interpretation, however, and in particular it is not clear whether contralateral suppression (CS) (defined as A/F(adrenal) ≤ A/F(peripheral) on the unaffected side) is important. We therefore performed a retrospective study to determine whether CS in surgically treated unilateral PA was associated with blood pressure (BP) and biochemical outcomes.

SETTING AND DESIGN

Patients who underwent unilateral adrenalectomy for PA after successful AVS were included if the lateralization index (A/F(dominant):A/F(nondominant)) was ≥ 2. Cases were reviewed at 6 to 24 months follow-up for outcomes with respect to the presence and degree of CS.

RESULTS

Sixty-six of 80 patients had CS. Baseline characteristics were similar. At postoperative follow-up, those with CS had lower systolic BP (SBP) (128 mm Hg vs 144 mm Hg, P = .001), a greater proportion with cure or improvement of hypertension (96% vs 64%, P = .0034), a greater proportion with biochemical cure of PA on fludrocortisone suppression testing (43 of 49 [88%] vs 4 of 9 [44%], P = .002) and were taking a lower median number of antihypertensive medications (0 vs 1.5, P = .0032). In a multivariate model, the degree of CS and preoperative SBP were both significantly correlated with postoperative SBP, but the lateralization index, sex, and age were not.

CONCLUSION

In this study, the presence of CS correlated with good BP and biochemical outcomes from surgery. This finding suggests that CS should be a factor in deciding whether to offer surgery for treatment of PA.