This document details the methodology for the Acute Kidney Injury Requiring New Inpatient Dialysis measure and should be reviewed along with the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List file, which contains the medical codes used in constructing the measure.
Episode-based cost measures represent the cost to Medicare for the items and services provided to a patient during an episode of care (“episode”). In all supplemental documentation, “cost” generally means the standardized Medicare allowed amount, and claims data from Medicare Parts A and B are used to construct the episode-based cost measures.
The Acute Kidney Injury Requiring New Inpatient Dialysis episode-based cost measure evaluates a clinician’s risk-adjusted cost to Medicare for beneficiaries who receive their first inpatient dialysis service for acute kidney injury during the performance period. The cost measure score is the clinician’s risk-adjusted cost for the episode group averaged across all episodes attributed to the clinician. This procedural measure includes costs of services that are clinically related to the attributed clinician’s role in managing care during each episode from the clinical event that opens, or “triggers,” the episode through 30 days after the trigger.
The annual expenditure of hospital-based AKI exceeds $10 billion, and each year there is approximately 600,000 cases of AKI. In 2015, 4.3 percent of Medicare beneficiaries experienced a hospitalization complicated by AKI. More specifically, over a nine-year span, over 1.09 million hospitalizations involved AKI requiring dialysis (AKI-D). Spending for hospitalizations with AKI-D showed an increase of $42,077 in hospitalization costs and an increase in length of stay by 11.5 days. The Acute Kidney Injury Requiring New Inpatient Dialysis episode-based cost measure was recommended for development by an expert clinician committee—the Renal Disease Management Clinical Subcommittee—because of its high impact in terms of patient population and Medicare spending, and the opportunity for incentivizing cost-effective, high-quality clinical care in this area. Based on the initial recommendations from the Clinical Subcommittee, the subsequent measure-specific workgroup provided extensive, detailed input on this measure.
The cost measure numerator is the sum of the ratio of observed to expected payment-standardized cost to Medicare for all Acute Kidney Injury Requiring New Inpatient Dialysis episodes attributed to a clinician. This sum is then multiplied by the national average observed episode cost to generate a dollar figure.
The cost measure denominator is the total number of episodes from the Acute Kidney Injury Requiring New Inpatient Dialysis episode group attributed to a clinician.
The Acute Kidney Injury Requiring New Inpatient Dialysis cost measure uses the following data sources:
- Medicare Parts A and B claims data from the Common Working File (CWF)
- Enrollment Data Base (EDB)
- Long Term Care Minimum Data Set (LTC MDS)
Methodologically, the Acute Kidney Injury Requiring New Inpatient Dialysis cost measure can be triggered based on claims data from the following settings: acute inpatient (IP) hospitals.
The cohort for this cost measure consists of patients who are Medicare beneficiaries enrolled in Medicare fee-for-service and who receive their first inpatient dialysis service for acute kidney injury that triggers an Acute Kidney Injury Requiring New Inpatient Dialysis episode.
The cohort for this cost measure is also further refined by the definition of the episode group and measure-specific exclusions (see Appendix A).
There are two overarching processes in calculating episode-based cost measure scores: episode construction (Steps 1-3) and measure calculation (Steps 4-6). This section provides a brief one-page summary of these processes for the Acute Kidney Injury Requiring New Inpatient Dialysis cost measure, and Appendix A describes the processes in detail.
- Trigger and define an episode: Episodes are defined by billing codes that open, or “trigger,” an episode. The episode window starts 90 days before the trigger and ends 30 days after the trigger. To enable meaningful clinical comparisons, episodes are placed into more granular, mutually exclusive sub-groups based on clinical criteria. Some episodes may also be excluded based on other information available at the time of the trigger.
- Attribute the episode to a clinician: For this procedural episode group, an attributed clinician is any clinician who bills a trigger code for the episode group on the day of the procedure for outpatient procedures or during the inpatient stay for inpatient procedures.
- Assign costs to the episode and calculate the episode observed cost: Clinically related services occurring during the episode window are assigned to the episode. The cost of the assigned services is summed to determine each episode’s standardized observed cost.
- Exclude episodes: Exclusions remove unique groups of patients from cost measure calculation in cases where it may be impractical and unfair to compare the costs of caring for these patients to the costs of caring for the cohort at large.
- Calculate expected costs for risk adjustment: Risk adjustment aims to isolate variation in clinician costs to only the costs that clinicians can reasonably influence (e.g., accounting for beneficiary age, comorbidities and other factors). A regression analysis is run using the risk adjustment variables as covariates to estimate the expected cost of each episode. Then, statistical techniques are applied to reduce the effect of extreme outliers on measure scores.
- Calculate the measure score: For each episode, the ratio of standardized total observed cost (from step 3) to risk-adjusted expected cost (from step 5) is calculated and averaged across all of a clinician or clinician group’s attributed episodes to obtain the average episode cost ratio. The average episode cost ratio is multiplied by the national average observed episode cost to generate a dollar figure for the cost measure score.
Measure Specifications Quick Reference
This page provides a quick, at-a-glance reference for the Acute Kidney Injury Requiring New Inpatient Dialysis episode-based cost measure specifications. More details on each component can be found in Appendix A, and the full list of codes and logic used to define each component can be found within the Measure Codes List file.
|Episode Window: During what time period are costs measured?|
|Pre-Trigger Window: 0 days||Post-Trigger Window: 30 days|
|Triggers: Patients receiving what medical care are included in the measure?|
|Service Assignment: Which clinically related costs are included in the measure?|
Assigned services generally fall within the following clinical themes:
|Risk Adjustors: Which risk factors are accounted for in the risk adjustment model?||Exclusions: Which populations are excluded from measure calculation?|
Appendix A. Detailed Measure Methodology
This section contains the technical details for the two overarching processes in calculating episode-based cost measure scores in more detail: Sections A.1 through A.3 describe episode construction and Sections A.4 through A.6 describe measure calculation.
Trigger and Define an Episode
Acute Kidney Injury Requiring New Inpatient Dialysis episodes are defined by Current Procedural Terminology / Healthcare Common Procedure Coding System (CPT/HCPCS) codes on Part B Physician/Supplier (Carrier) claims that open, or trigger, an episode. For the codes and logic relevant to this section please see the “Triggers” and “Triggers_Details” tabs of the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List.
The steps for defining an episode for the Acute Kidney Injury Requiring New Inpatient Dialysis episode group are as follows:
- Identify Part B Physician/Supplier claim lines with positive standardized payment that have a trigger code. A trigger code is either (i) a procedure code for dialysis during an IP stay, or (ii) a relevant IP E&M service code billed by a nephrologist during an IP stay.
- Identify the first IP stay that is concurrent to the expense date for the trigger Part B Physician/Supplier claim line.
- Trigger an episode if all the following conditions are met for an identified Part B Physician/Supplier claim line:
- It was billed by a clinician of a specialty that is eligible for MIPS for trigger codes related to (i).
- It was billed by a nephrologist, for trigger codes related to (ii).
- It does not have a post-operative modifier code.
- It is the highest cost claim line across all claim lines identified in the above bullets and that have any Acute Kidney Injury Requiring New Inpatient Dialysis trigger code billed for the beneficiary on that day. If multiple Part B Physician/Supplier claim lines with a trigger code occur on different days within a concurrent IP stay, an episode will be triggered by the claim line with the earliest expense date during the IP stay.
- Establish the episode window as follows:
- Establish the episode trigger date as the expense date of the trigger claim line identified in the “Trigger an episode” bullet above.
- Establish the episode start date as the episode trigger date.
- Establish the episode end date as 30 days after the episode trigger date.
Attribute Episodes to a Clinician
Once an episode has been triggered and defined, it is attributed to one or more clinicians of a specialty that is eligible for MIPS. Clinicians are identified by Taxpayer Identification Number (TIN) and National Provider Identifier (NPI) pairs (TIN-NPI), and clinician groups are identified by TIN. Only clinicians of a specialty that is eligible for MIPS or clinician groups where the triggering clinician is of a specialty that is eligible for MIPS are attributed episodes. For codes relevant to this section, please see the “Attribution” tab of the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List.
The steps for attributing an Acute Kidney Injury Requiring New Inpatient Dialysis episode are as follows:
- Identify claim lines with positive standardized payment for any trigger codes that occur during the IP stay, if the triggering procedure occurs during an IP stay with a relevant DRG, otherwise identify claim lines with positive standardized payment for any trigger codes that occur on the trigger day.
- Designate a TIN-NPI as a main clinician if the following conditions are met:
- No assistant modifier code is found on one or more claim lines billed by the clinician.
- No exclusion modifier code is found on the same claim line.
- Designate a TIN-NPI as an assistant clinician if the following conditions are met:
- The TIN-NPI was not designated as a main clinician.
- An assistant modifier code is found.
- No exclusion modifier code is found.
- Attribute an episode to any TIN-NPI designated as a main or assistant clinician.
- Attribute episodes to the TIN by aggregating all episodes attributed to NPIs that bill to that TIN. If the same episode is attributed to more than one NPI within a TIN, the episode is attributed only once to that TIN.
Future attribution rules may benefit from the implementation of patient relationship categories and codes. As required by section 101(f) of MACRA, CMS will consider how to incorporate the patient relationship categories into episode-based cost measurement methodology as clinicians and billing experts gain experience with them.
Assign Costs to an Episode and Calculate Total Observed Episode Cost
Services, and their Medicare costs, are assigned to an episode only when clinically related to the attributed clinician’s role in managing patient care during the episode. Assigned services may include treatment and diagnostic services, ancillary items, services directly related to treatment, and those furnished as a consequence of care (e.g., complications, readmissions, unplanned care, and emergency department visits). Unrelated services are not assigned to the episode. For example, the cost of care for a chronic condition that occurs during the episode but is not related to the clinical management of the patient relative to the inpatient dialysis service for acute kidney injury would not be assigned.
To ensure that only clinically related services are included, services during the episode window are assigned to the episode based on a series of service assignment rules, which are listed in the “Service_Assignment” tab of the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List file.
For the Acute Kidney Injury Requiring New Inpatient Dialysis episode group, only services performed in the following service categories are considered for assignment to the episode costs:
- Emergency Department (ED)
- Outpatient (OP) Facility and Clinician Services
- IP – Medical
- IP – Surgical
In addition to service category, service assignment rules may be modified based on the service category in which the service is performed, as listed above. Service assignment rules may also be defined based on specific (i) service information alone or service information combined with diagnosis information, (ii) prior incidence of service, and/or (iii) the timing of the service, as detailed below.
- Services may be assigned to the episode based on the following service information combinations:
- High level service code alone
- High level service code combined with first three digits of the International Classification of Diseases – Tenth Revision diagnosis code (3-digit ICD-10 diagnosis code)
- High level service code combined with full ICD-10 diagnosis code
- High level service code combined with more specific service code
- High level service code combined with more specific service code and with 3-digit ICD-10 diagnosis code
- High level service code combined with more specific service code and with full ICD-10 diagnosis code
- Assigned services may be further refined by prior incidence of service or diagnosis:
- Services may be assigned unconditionally (regardless of prior incidence of the service in patient’s recent claims history)
- Services may be assigned if newly occurring
- Services may be assigned in combination with a diagnosis if the service is newly occurring
- Services may be assigned in combination with a diagnosis if the diagnosis is newly occurring
- Services may be assigned in combination with a diagnosis if either the service OR the diagnosis are newly occurring
- Services may be assigned in combination with a diagnosis if both the service AND the diagnosis are newly occurring
- Services as defined by the applicable combinations and incidence options above may be assigned with only specific timing:
- Services may be assigned based on whether or not the service occurs before the trigger (in the pre-trigger window) and/or after the trigger (in the post-trigger window)
- Services may be assigned only if they occur within a particular number of days from the trigger within the episode window, and services may be assigned for a period shorter than the full duration of the episode window
The steps for assigning costs are as follows:
- Identify all services on claims with positive standardized payment that occur within the episode window.
- Assign identified services to the episode based on the types of service assignment rules described above.
- Assign skilled nursing facility (SNF) claims based on the following criteria:
- Identify SNF claims for which both (i) the SNF claim’s qualifying IP stay is the IP stay during which the trigger occurs, if an IP stay is found, and (ii) the SNF claim occurs during the episode window.
- For those identified SNF claims, assign the percentage of the claim amount proportional to the portion of the SNF claim that overlaps with the episode window.
- Assign all claims with trigger codes occurring during the trigger day/stay.
- Assign all physician claims and DME claims occurring during concurrent IP stay.
- Assign all inpatient E&M claims during IP stays in the post-trigger window assigned to episode.
- Sum standardized Medicare allowed amounts for all claims assigned to each episode to obtain the standardized total observed episode cost.
Service Assignment Example
- Clinician A performs surgical treatment for renal or ureteral stones for Patient K. This service triggers a Renal or Ureteral Stone Surgical Treatment episode, which is attributed to Clinician A.
- Clinician B treats the patient for post-operative urinary tract infection (UTI), which is considered a clinically related service, during the episode window.
- Because post-operative treatment for UTI during the episode window is considered to be clinically related to the initial surgical treatment for renal or ureteral stones, the cost of the post-operative treatment for UTI will be assigned to Clinician A’s Renal or Ureteral Stone Surgical Treatment episode.
Before measure calculation, episode exclusions are applied to remove certain episodes from measure score calculation. Certain exclusions are applied across all procedural episode groups, and other exclusions are specific to this measure, based on consideration of the clinical characteristics of a homogenous patient cohort. All measure-specific exclusions are listed in the “Exclusions” and “Exclusions_Details” tabs in the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List file.
The steps for episode exclusion are as follows:
- Exclude episodes from measure calculation if:
- The beneficiary has a primary payer other than Medicare for any time overlapping the episode window or 120-day lookback period prior to the trigger day.
- The beneficiary was not enrolled in Medicare Parts A and B for the entirety of the lookback period plus episode window, or was enrolled in Part C for any part of the lookback plus episode window.
- No main clinician is attributed the episode.
- The beneficiary’s date of birth is missing.
- The beneficiary’s death date occurred before the episode ended.
- The episode trigger claim was not performed in an ambulatory/office-based care, IP hospital, OP hospital, or ASC setting based on its place of service.
- The IP facility is not a short-term stay acute hospital as defined by subsection (d) when an IP stay concurrent with the trigger is found.
- Apply measure-specific exclusions, which check the beneficiary’s Medicare claims history for certain billing codes (as specified in the Measure Codes List file) that indicate the presence of a particular procedure, condition, or characteristic.
Estimate Expected Costs through Risk Adjustment
Risk adjustment is used to estimate expected episode costs in recognition of the different levels of care beneficiaries may require due to comorbidities, disability, age, and other risk factors. The risk adjustment model includes variables from the CMS Hierarchical Condition Category Version 22 (CMS-HCC V22) 2016 Risk Adjustment Model,16 as well as other standard risk adjustors (e.g., beneficiary age) and variables for clinical factors that may be outside the attributed clinician’s reasonable influence. A full list of risk adjustment variables can be found in the “RA” and “RA_Details” tabs of the Acute Kidney Injury Requiring New Inpatient Dialysis Measure Codes List file.
Steps for defining risk adjustment variables and estimating the risk adjustment model are as follows:
- Define HCC and episode group-specific risk adjustors using service and diagnosis information found on the beneficiary’s Medicare claims history in the 120-day period prior to the episode trigger day (or the timing specified in the “RA_Details” tab of the Measure Codes List file) for certain billing codes that indicate the presence of a procedure, condition, or characteristic.
- Define other risk adjustors that rely upon Medicare beneficiary enrollment and assessment data as follows:
- Identify beneficiaries who are originally “Disabled without end-stage renal disease (ESRD)” or “Disabled with ESRD” using the original reason for joining Medicare field in the Medicare beneficiary enrollment database (EDB).
- Identify beneficiaries with ESRD if their enrollment indicates ESRD coverage, ESRD dialysis, or kidney transplant in the Medicare beneficiary enrollment database in the lookback period.
- Identify beneficiaries who have spent at least 90 days in a long-term care institution without having been discharged to the community for 14 days, based on MDS assessment data.
- Drop risk adjustors that are defined for less than 15 episodes nationally for each sub-group to avoid using very small samples.
- Categorize beneficiaries into age ranges using their date of birth information in the Medicare beneficiary enrollment database. If an age range has a cell count less than 15, collapse this in the next adjacent age range category towards the reference category (65-69).
- Include the MS-DRG of the episode’s trigger IP stay, if an IP stay is found, as a categorical risk adjustor.
- Run an ordinary least squares (OLS) regression model to estimate the relationship between all the risk adjustment variables and the dependent variable, the standardized observed episode cost, to obtain the risk-adjusted expected episode cost. A separate OLS regression is run for each episode sub-group nationally.
- Winsorize expected costs as follows.
- Assign the value of the 0.5th percentile to all expected episode costs below the 0.5th percentile.
- Renormalize values by multiplying each episode’s winsorized expected cost by the sub-group’s average expected cost, and dividing the resultant value by the sub-group’s average winsorized expected cost.
- Exclude episodes with outliers as follows. This step is performed separately for each sub-group.
- Calculate each episode’s residual as the difference between the re-normalized, winsorized expected cost computed above and the observed cost.
- Exclude episodes with residuals below the 1st percentile or above the 99th percentile of the residual distribution.
- Renormalize the resultant expected cost values by multiplying each episode’s winsorized expected costs after excluding outliers by the sub-group’s average standardized observed cost across all episodes originally in the risk adjustment model, and dividing by the sub-group’s average winsorized expected cost after
Calculate Measure Scores
Measure scores are calculated for a TIN or TIN-NPI as follows:
- Calculate the ratio of observed to expected episode cost for each episode attributed to the clinician/clinician group.
- Calculate the average ratio of observed to expected episode cost across the total number of episodes attributed to the clinician/clinician group.
- Multiply the average ratio of observed to expected episode cost by the national average observed episode cost to generate a dollar figure representing risk-adjusted average episode cost.
The clinician-level or clinician group practice-level risk-adjusted cost for any attributed clinician (or clinician group practice) “j” can be represented mathematically as:
|???||is the standardized payment for episode i and attributed clinician (or clinician group practice) j|
|? ??||is the expected standardized payment for episode i and clinician (or clinician group practice) j, as predicted from risk adjustment|
|??||is the number of episodes for clinician (or clinician group practice) j|
|?||is the total number of TIN/TIN-NPI attributed episodes nationally|
|is all episodes i in the set of episodes attributed to clinician (or clinician group practice) j|
A diagram demonstrating a visual depiction of an example measure calculation can be found in Appendix B.
Appendix B. Measure Calculation Example
The diagram below provides an illustrated example of measure calculation, using an example measure where the clinician has only four attributed episodes for demonstration purposes. For more details on measure calculation, please refer to Section A.6.