Getting to the cause of Chronic Kidney Disease of unknown cause (CKDu): Research protocol and baseline results

This paper outlines a research protocol and baseline results for a prospective multi-regional study in Nicaragua, South India, and Sri Lanka aimed at identifying the environmental and occupational causes—specifically metals, agrochemicals, infections, and heat/dehydration—of the epidemic of Chronic Kidney Disease of unknown cause (CKDu) affecting agricultural communities in low-and-middle-income countries.

The Gist

The Mystery of the Silent Kidney Epidemic

Imagine a group of young, healthy farmers in three different parts of the world—Nicaragua, India, and Sri Lanka. They are working hard in the sun, but their kidneys are quietly failing. This isn't the usual kind of kidney failure caused by diabetes or high blood pressure. It's a strange, silent epidemic affecting people who shouldn't be sick. Doctors call this CKDu (Chronic Kidney Disease of unknown cause).

Think of CKDu like a ghost in the machine. The machine (the kidney) stops working, but the usual warning lights (like high blood sugar or protein in the urine) never turn on until it's too late. By the time the problem is found, the damage is often irreversible, and in many of these poor regions, there is no dialysis or transplant available. This has led to the premature deaths of tens of thousands of young adults.

The Big Question: What is the Killer?

For years, scientists have been playing detective, but they've been looking at the crime scene from different angles.

• In Central America, some suspect the scorching heat and dehydration are the culprits.
• In South Asia, the suspicion falls on heavy metals in the water or pesticides.

The problem is that everyone has been using different magnifying glasses. Some studies looked at sick people and asked them what they did years ago (which is like asking a witness to remember a car crash from memory—details get fuzzy). Others just took a snapshot of kidney function once, which isn't enough to see the slow decline.

The New Plan: A Global Team with One Rulebook

This paper is the instruction manual for a massive new investigation. Instead of guessing, the researchers have set up three long-term "follow-up" teams in Nicaragua, India, and Sri Lanka.

Think of this like planting a garden and watching it grow, rather than just looking at the dead plants at the end of the season.

1. The Participants: They recruited thousands of healthy young adults who don't have kidney disease yet.
2. The Routine: Every year, these people come in for a check-up. They answer detailed questions about their work, their water, and their health. They give blood and urine samples.
3. The Goal: By tracking the same people over several years, the scientists can see exactly when and how their kidney function starts to drop. This helps them figure out what happened before the damage started, rather than just guessing after the fact.

The Four Suspects

The researchers are testing four main theories about what is poisoning these kidneys. They are treating these theories like suspects in a lineup:

1. The Metal Men (Metals & Metalloids): Could there be invisible poisons like arsenic or lead in the water or soil? They will test urine samples to see if these metals are hiding inside the body.
2. The Chemical Sprayers (Agrochemicals): Could the pesticides farmers use be the problem? They will look for traces of these chemicals in the body.
3. The Invisible Invaders (Infections): Could a bug or virus (like a specific type of bacteria or virus common in hot climates) be attacking the kidneys? They will check the blood for signs of past infections.
4. The Heat Haze (Heat & Dehydration): Is working in the blistering sun without enough water the main cause? Since there is no "heat test" for the body, they will use a clever mix of questionnaires and weather data to build a "heat map" for every single person, estimating exactly how much heat stress they endured.

The High-Tech Detective Work

To solve this, the team is using some serious science tools:

• The "Time Machine" (Longitudinal Data): Instead of one snapshot, they are making a movie of kidney health over time. This is crucial because kidney function can bounce up and down day-to-day. They need to see the trend to find the real cause.
• The "Fingerprint Scanner" (Genetics & Proteomics): They are looking at the participants' DNA to see if some people are genetically more vulnerable. They are also analyzing proteins in the urine to find a "fingerprint" of the specific damage happening inside the kidney, hoping to find a marker that shows the disease early.
• The "Global Comparison" (Harmonization): The most important part is that all three teams are using the exact same rules and tools. This means if they find a problem in Nicaragua, they can immediately check if that same problem exists in India. If the causes are different, they will find out. If the causes are the same, they will find out that too.

Why This Matters

This paper doesn't claim to have found the answer yet. It's the blueprint for the search.

The researchers admit there are challenges. Keeping people in the study for years is hard, and they can't easily test the soil or water in every single village. But by combining long-term tracking, high-tech lab tests, and a unified approach across three continents, they hope to finally unmask the "ghost" that is killing these young workers.

In short: They are building a global team of detectives, giving them the same magnifying glass, and asking them to watch the same crime unfold over time, so they can finally catch the culprit.

Technical Summary

Based on the provided preprint, here is a detailed technical summary of the research protocol and baseline results for the study on Chronic Kidney Disease of unknown cause (CKDu).

1. Problem Statement

Chronic Kidney Disease of unknown cause (CKDu) is an epidemic primarily affecting agricultural communities in low-and-middle-income countries (LMICs). It is characterized by tubular-interstitial pathology, distinct from CKD caused by diabetes, hypertension, or glomerular nephritis.

• Impact: It leads to premature death among young adults (18–38 years) in affected regions, with tens to hundreds of thousands of deaths estimated over the last two decades.
• Current Knowledge Gap: While CKDu is confirmed in Central America (Nicaragua) and South Asia (India, Sri Lanka), the etiology remains unknown. Hypotheses vary by region:
  • Central America: Heat stress, dehydration, and agrochemicals.
  • South Asia: Heavy metals in water and pesticides.
• Methodological Limitations: Previous research relied heavily on cross-sectional surveys and retrospective data, which suffer from reverse causation, recall bias, and an inability to distinguish initiating causes from exacerbating factors. Furthermore, single eGFR measurements are insufficient for early detection due to biological variability, and renal biopsies often occur too late to identify the initiating exposure.

2. Methodology

The study establishes a multi-center, prospective cohort design across three endemic regions: Nicaragua, South India (Andhra Pradesh), and Sri Lanka (Anuradhapura). The core strategy involves tracking within-person changes in kidney function over time using standardized protocols.

Study Design & Cohorts

• Participants: Healthy men and women (ages 18–60) without pre-existing CKD, diabetes, or hypertension.
• Follow-up: Minimum of four years with annual visits.
• Retention: High retention rates reported (e.g., Nicaragua ~86%, Sri Lanka ~96-98%).
• Data Collection:
  • Clinical: Height, weight, blood pressure (digital sphygmomanometer), and serum creatinine (measured locally and re-quantified centrally using IDMS-traceable reference methods).
  • Primary Outcome: Trajectory of estimated Glomerular Filtration Rate (eGFR) over time, calculated using the CKD-EPI equation.
  • Questionnaires: Standardized instruments capturing demographics, occupational history, hydration patterns, medication use, and specific environmental exposures.

Exposure Assessment (Workstreams)

The study targets four primary hypothesized causes using direct biological measurement and modeling:

1. Metals and Metalloids: Urine analysis via Inductively-Coupled Plasma – Mass Spectrometry (ICP-MS) for arsenic, cadmium, lead, mercury, etc.
2. Agrochemicals: Analysis of unmodified chemicals (e.g., glyphosate) and metabolites (e.g., pyrethroids) in urine using LC-MS/MS.
3. Infections: Serological testing (ELISA) for IgG antibodies against nephrotropic pathogens (Hantaviruses, Leptospira spp.) and metagenomic analysis.
4. Heat/Dehydration: Construction of a Heat-Exposure-Matrix combining self-reported time-activity diaries, symptom questionnaires, and high-resolution climate data (ERA-5 reanalysis) to estimate chronic heat stress.

Molecular & Genetic Analysis

• Genomics: Genome-wide association studies (GWAS) using Illumina Global Screening Array-24 to identify genetic risk loci and gene-environment interactions.
• Proteomics: Discovery proteomics of urine samples to identify early biomarkers, addressing the lack of albuminuria in early CKDu stages.

3. Key Contributions

• Harmonized Multi-Regional Protocol: This is the first study to apply identical, rigorous prospective protocols across geographically distinct endemic regions (Central America and South Asia), allowing for direct comparison of exposure-outcome relationships.
• Shift to Longitudinal Trajectories: Moving away from single-point prevalence to within-individual eGFR decline, which offers higher sensitivity for detecting early disease in populations with normal baseline renal function.
• Comprehensive Exposure Biomonitoring: The integration of direct biological measurements (metals, agrochemicals, pathogens) with environmental modeling (heat stress) addresses the lack of biomarker data in previous CKDu research.
• Bioresource Creation: Establishment of a centralized biobank (urine and blood) from three well-characterized cohorts to facilitate future hypothesis testing.

4. Results (Baseline and Protocol Status)

Note: As this is a protocol paper with baseline results, it reports on study establishment and recruitment rather than final causal conclusions.

• Recruitment Success:
  • Nicaragua: Established in 11 communities; recruited ~700+ participants across three phases (2014–2021) with high retention.
  • Sri Lanka: Recruited 729 participants in 2018 from high-prevalence areas; follow-up rates exceeded 96% over three years.
  • India: Baseline survey of 1,637 residents in Prakasam district; identified 206 eligible cohort participants from high-prevalence villages.
• Feasibility: The study demonstrates that high-quality, standardized data collection and biospecimen storage are feasible in resource-limited settings, with successful implementation of IDMS-standardized creatinine measurement and mobile data collection (ODK).
• Preliminary Findings: The paper notes that previous biopsies in these regions consistently show interstitial fibrosis and tubular atrophy but fail to identify a specific toxin, reinforcing the need for the longitudinal exposure tracking proposed here.

5. Significance

• Causal Inference: By addressing temporality (exposure preceding decline) and controlling for confounders through longitudinal design, this study aims to definitively identify the primary etiological drivers of CKDu, distinguishing them from factors that merely accelerate progression.
• Public Health Intervention: Identifying the specific cause (e.g., a specific metal, pesticide, or heat threshold) is critical for developing targeted preventive interventions in LMICs where renal replacement therapy is scarce.
• Global Health Impact: If a common cause is identified across regions, it could lead to global policy changes regarding agricultural practices and water safety. If causes differ, it allows for region-specific mitigation strategies.
• Methodological Advancement: The protocol sets a new standard for nephro-epidemiology in LMICs, demonstrating how to overcome challenges like lack of routine health data and limited access to advanced diagnostics through community-based prospective research.

Limitations Noted:

• Lack of longitudinal environmental sampling (soil/water) in India and Sri Lanka (only Nicaragua collected these initially), limiting direct correlation between environmental and biological toxicant levels.
• Potential selection bias due to loss to follow-up in economically vulnerable populations, though current retention rates are high.