Point-of-Care Testing in Chronic Kidney Disease of Non-Traditional Origin: Considerations for Clinical, Epidemiological, and Health Surveillance Research and Practice.

Purpose: As the prevalence of chronic kidney disease of non-traditional origin (CKDnt) rises in low-resource settings, there is a need for reliable point-of-care creatinine testing. The purpose of this analysis was to assess the accuracy of two commonly used point-of-care creatinine devices, the i-STAT handheld (Abbott, Princeton, NJ, USA) and the StatSensor Creatinine (Nova Biomedical, Waltham, MA, USA) in comparison to venipuncture serum creatinine measures. The affordability, sensitivity, specificity, ease of use, and other considerations for each device are also presented. Methods: Three paired data sets were compared. We collected 213 paired i-STAT and venipuncture samples from a community study in Nicaragua in 2015-2016. We also collected 267 paired StatSensor Creatinine and venipuncture samples, including 158 from a community setting in Nicaragua in 2014-2015 and 109 from a Guatemala sugarcane worker cohort in 2017-2018. Pearson correlation coefficients, Bland-Altman plots, and no intercept linear regression models were used to assess agreement between point-of-care devices and blood samples. Results: The i-STAT performed the most accurately, overestimating creatinine by 0.07 mg/dL (95% CI: 0.02, 0.12) with no evidence of proportional bias. The StatSensor Creatinine performed well at low levels of creatinine (Mean (SD): 0.87 (0.19)). Due to proportional bias, the StatSensor Creatinine performed worse in the Nicaragua community setting where creatinine values ranged from 0.31 to 7.04 mg/dL. Discussion: Both devices provide acceptable sensitivity and specificity. Although adequate for routine surveillance, StatSensor Creatinine is less accurate as the values of measured creatinine increase, a consideration when using the point-of-care device for screening individuals at risk for CKDnt. Research, clinical, and screening objectives, cost, ease of use, and background prevalence of disease must all be carefully considered when selecting a point-of-care creatinine device. Conclusion: POC testing can be more accessible in resource-limited settings. The selection of the appropriate device will depend on the use-case.

Prevalence and Risk Factors for CKD Among Brickmaking Workers in La Paz Centro, Nicaragua.

RATIONALE & OBJECTIVE: In Central America, there is a high prevalence of chronic kidney disease (CKD) of nontraditional etiology often observed among agricultural workers. Few studies have assessed CKD prevalence among workers in nonagricultural occupations, which was the objective of this investigation. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: Male and female workers (n = 224) employed by artisanal brickmaking facilities in La Paz Centro, Nicaragua. PREDICTORS: Age, sex, education, smoking status, body mass index, alcohol consumption, water consumption, first-degree relative(s) with CKD, years worked, hours worked per week, job category, study visit (baseline and follow-up), and self-reported hypertension and diabetes. OUTCOMES: CKD defined as estimated glomerular filtration rate (eGFR) < 60mL/min/1.73m2 at 2 time points 4 months apart and CKD stage. ANALYTICAL APPROACH: A linear mixed-effects model with an unstructured covariance matrix was used to evaluate the association between demographics, occupational risk factors, and eGFR at baseline. The interaction between risk factors and time with change in eGFR was also evaluated. Multivariable logistic regression models were used to evaluate predictors of CKD. RESULTS: The CKD prevalence was 12.1% (n = 27), 100% of cases were male, 30% had stage 5 CKD (eGFR < 15mL/min/1.73m2), and 22% were younger than 35 years. Proportions of participants with eGFRs < 60mL/min/1.73m2 at baseline and follow-up were 13.8% and 15.2%, respectively. Linear regression analysis demonstrated significant predictors of lower kidney function at baseline including oven work, older age, lack of education, and having an immediate family member with CKD. Predictors of CKD identified using logistic regression analysis included oven work and lack of education. LIMITATIONS: Crude job classification measures, loss to follow-up, self-reported exposures. CONCLUSIONS: The prevalence of CKD is high in this population of brick workers, suggesting that the epidemic of CKD affecting Mesoamerica is not limited to agricultural workers. These results are consistent with the hypothesis that occupational heat exposure is a risk factor for kidney disease in this region.

Acute Kidney Injury in Sugarcane Workers at Risk for Mesoamerican Nephropathy.

RATIONALE & OBJECTIVE: Mesoamerican nephropathy (MeN), a form of chronic kidney disease (CKD) of unknown cause in Central America, affects young individuals working in physically strenuous occupations. Repeated episodes of work-related kidney injury may lead to CKD in this setting. We aimed to better understand the burden and natural history of acute kidney injury (AKI) in workers at risk for MeN. STUDY DESIGN: Cross-sectional study of active sugarcane workers, followed by prospective follow-up of individuals with AKI. SETTING & PARTICIPANTS: 326 sugarcane workers with normal preharvest serum creatinine (Scr) values and no history of CKD in an MeN hotspot in Nicaragua near the end of the harvest, and prospective follow-up of workers with AKI. PREDICTOR: AKI during the harvest, as defined by Scr level increase ≥ 0.3mg/dL over baseline to a level ≥ 1.3mg/dL. OUTCOMES: Kidney function trajectory and development of CKD over 12 months. ANALYTICAL APPROACH: Linear regression models were used to analyze the association between job category and kidney function. For workers with AKI, the effect of time on Scr level was evaluated using linear mixed effects. RESULTS: 34 of 326 participants were found to have AKI, with a median late-harvest Scr level of 1.64mg/dL in the AKI group. Workers without AKI had a median Scr level of 0.88mg/dL. AKI was more common among cane cutters compared with other field workers. Participants with AKI had variable degrees of kidney function recovery, with median 6- and 12-month Scr values of 1.25 and 1.27mg/dL, respectively (P < 0.001 for each follow-up value compared to late-harvest Scr). When we compared workers' kidney function before the AKI episode to their kidney function at last follow-up, 10 participants with AKI developed de novo estimated glomerular filtration rate < 60mL/min/1.73m2 and 11 had a >30% decrease in estimated glomerular filtration rate. LIMITATIONS: Follow-up limited to 1 year and some loss to follow-up in the prospective component of the study. Broad definition of AKI that includes both acute and subacute kidney injury. CONCLUSIONS: In a group of sugarcane workers with normal preharvest kidney function, newly decreased kidney function developing during the harvest season was common. Of those with kidney injury, nearly half had established CKD 12 months later.

Characterization of Mesoamerican Nephropathy in a Kidney Failure Hotspot in Nicaragua.

BACKGROUND: Mesoamerican nephropathy (MeN) is a kidney disease of unknown cause that mainly affects working-age men in Central America. Despite being a major cause of morbidity and mortality in this region, its clinical characteristics have not been well defined. STUDY DESIGN: Cross-sectional family-based study. SETTING & PARTICIPANTS: 266 members of 24 families with high chronic kidney disease (CKD) burdens in a MeN hotspot in Northwestern Nicaragua. We compared clinical and biochemical characteristics of affected individuals first with their unaffected relatives and then with NHANES (National Health and Nutrition Examination Survey) participants with CKD in order to reveal identifying features of MeN. PREDICTOR: CKD defined as serum creatinine level ≥ 1.5mg/dL in men and ≥1.4mg/dL in women. OUTCOMES: Clinical and biochemical parameters, including serum sodium, potassium, bicarbonate, calcium, magnesium, phosphorus, and uric acid. RESULTS: Hyperuricemia, in many cases severe, was common among patients with MeN. Uric acid levels in patients with MeN were higher than those in NHANES participants (mean, 9.6 vs 7.4mg/dL for men in each group) despite more frequent use of uric acid-lowering medications in Nicaraguan individuals (71.7% vs 11.2%). In multivariable linear mixed-effects regression analysis, uric acid levels were 2.0mg/dL (95% CI, 1.0-3.0; P<0.001) higher in patients with MeN compared with their NHANES counterparts after adjusting for age, estimated glomerular filtration rate, and uric acid-lowering therapies. In contrast to prior reports, hyponatremia and hypokalemia were not common. LIMITATIONS: CKD defined by single serum creatinine measurement; population likely not representative of full MeN phenotype spectrum across Central America; major differences between MeN and NHANES groups in important characteristics such as age, ancestry, and recruitment method. CONCLUSIONS: Hyperuricemia out of proportion to the degree of decreased kidney function was common among Nicaraguan patients with MeN. Our results suggest that rather than being solely a consequence of CKD, hyperuricemia may play a role in MeN pathogenesis, a hypothesis that deserves further study.

Urine biomarkers of kidney injury among adolescents in Nicaragua, a region affected by an epidemic of chronic kidney disease of unknown aetiology.

BACKGROUND: An epidemic of chronic kidney disease (CKD) of non-traditional aetiology has been recently recognized by health authorities as a public health priority in Central America. Previous studies have identified strenuous manual work, agricultural activities and residence at low altitude as potential risk factors; however, the aetiology remains unknown. Because individuals are frequently diagnosed with CKD in early adulthood, we measured biomarkers of kidney injury among adolescents in different regions of Nicaragua to assess whether kidney damage might be initiated during childhood. METHODS: Participants include 200 adolescents aged 12-18 years with no prior work history from four different schools in Nicaragua. The location of the school served as a proxy for environmental exposures and geographic locations were selected to represent a range of factors that have been associated with CKD in adults (e.g. altitude, primary industry and CKD mortality rates). Questionnaires, urine dipsticks and kidney injury biomarkers [interleukin-18, N-acetyl-d-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL) and albumin-creatinine ratio] were assessed. Biomarker concentrations were compared by school using linear regression models. RESULTS: Protein (3.5%) and glucose (1%) in urine measured by dipstick were rare and did not differ by school. Urine biomarkers of tubular kidney damage, particularly NGAL and NAG, showed higher concentrations in those schools and regions within Nicaragua that were defined a priori as having increased CKD risk. Painful urination was a frequent self-reported symptom. CONCLUSIONS: Although interpretation of these urine biomarkers is limited because of the lack of population reference values, results suggest the possibility of early kidney damage prior to occupational exposures in these adolescents.