Concept: Risk of Chronic Kidney Disease (CKD) Progression to End Stage Kidney Disease (ESKD) - Heat Map

Introduction

This concept describes the methods developed to measure the risk of chronic kidney disease (CKD) progression to end stage kidney disease (ESKD) as it was used in the Care of Manitobans Living with Chronic Kidney Disease deliverable by Chartier et al. (2015). This includes the age groups applied, the data sources used, the code values and conditions identifying the ranges employed in the measurements, and additional conditions / restrictions that are applied. A "heat map", originally developed by the Kidney Disease Improving Global Outcomes (KDIGO) work group (2013) and adapted for use in our research, is described and illustrates the risk of progression to ESKD. A link to the adapted "heat map" used in the deliverable is also provided.

Technical Definition of Risk of Progression

The technical definition for the risk of chronic kidney disease (CKD) progression to end stage kidney disease (ESKD) as described in Chartier et al. (2015) is as follows:


• Age Groups:
  
  • Children: 0-17 years old
    
  • Adults: 18 years and older
  
  
• Data Sources:
  
  • Diagnostic Services Manitoba (DSM) - now named Shared Health Diagnostic Services (SHDS) - Chemistry Data
  
  
• Code Values and Conditions: - The prognosis of CKD in Manitoba residents was evaluated based on the latest available laboratory results in the period April 1 2006 – March 31 2012. The following categories for albuminuria and estimated glomerular filtration rate (eGFR) were used to define increasing levels of kidney failure risk:

  Persistent Albuminuria Categories
  

  • A1 (normal to mildly increased): ACR <3 mg/mmol or PCR <15 mg/mmol
    
  • A2 (moderately increased): ACR 3-30 mg/mmol or PCR 15-50 mg/mmol
    
  • A3 (severely increased): ACR >30 mg/mmol or PCR >50 mg/mmol
    
    NOTE:
    
    • ACR = Albumin-Creatinine Ratio (ACR)
      
    • PCR = Protein-Creatinine Ratio (PCR)

  
  eGFR categories
  

  • G1 (normal or high): eGFR values >=90
    
  • G2 (mildly decreased): eGFR values within 60-89
    
  • G3a (mildly to moderately decreased): eGFR values within 45-59
    
  • G3b (moderately to severely decreased): eGFR values within 30-44
    
  • G4 (severely decreased): eGFR values within 15-29
    
  • G5 (kidney failure): eGFR values <15
    
    Note: The G1 and G2 categories in adults were combined to produce a category for normal eGFR of >= 60.

The Heat Map - Mapping Categories of Risk

To determine the likelihood of progression to ESKD, we adapted a "heat map" (a colour-coded classification table) developed in January 2013 by the Kidney Disease Improving Global Outcomes (KDIGO) Work Group (Kidney Disease Improving Global Outcomes (KDIGO), 2013). This new approach for prognosis of CKD was built on the recognition that albuminuria is an important marker of kidney function and risk of progression to ESKD, and it uses both albuminuria categories and eGFR to identify four levels of risk:


• green: lowest risk (eGFR and albuminuria are normal or mildly abnormal)
  
• yellow: moderately increased risk
  
• orange: high risk
  
• red: the highest risk of all.

We modified this table by adding three additional categories to represent people with CKD who have an incomplete set of laboratory tests (one of the two laboratory tests, providing some indications of risk level) or who do not have any laboratory tests (unknown risk level). These additional categories included:


• light purple: likely at lower risk
  
• dark purple: likely at higher risk, and
  
• white: unknown risk.

In the event that only one of albuminuria or eGFR could be categorized, those who also met the administrative definition for CKD were assigned the following risk categories:


• Low Risk: Albuminuria A1 or A2, or eGFR G1, G2 or G3a.
  
• High Risk: Albuminuria A3 or eGFR G3b, G4 or G5.

Those who met the administrative definition of CKD with no laboratory data to provide information about severity of risk were assigned to the Unknown Risk category.

We combined all of these categories into three overall risk levels: low risk (green, yellow, and light purple), high risk (orange, red, and dark purple) and unknown risk (white). The low risk group includes people who might be in earlier stages of CKD, and the high risk group includes people who might be in later stages of CKD. We were not able to determine how advanced the disease is in people in the unknown risk group (white) because of lack of laboratory data and thus have no information about the impairment of kidney function.

For more information on how the heat map was developed for this project, and a table illustrating the modified categories, see the section titled Risk of progression to ESKD in the deliverable.