CurrentBlue Cross Blue Shield - WisconsinPolicy N/A

Lung Allocation Score (LAS) calculation guide

Explains how the Lung Allocation Score is computed for lung transplant candidates, describing inputs, stepwise calculation, and parameter tables used to prioritize candidates based on waitlist urgency and expected first-year post-transplant survival.

Policy Summary

PayerBlue Cross Blue Shield - Wisconsin

PolicyLung Allocation Score (LAS) calculation guide

Policy CodePolicy N/A

Change TypeInformational — no coverage or authorization changes in excerpt

Effective DateN/A

Next Review DateN/A

Key ActionProvide complete candidate clinical variables and required survival-table inputs so the LAS can be computed accurately.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

0–100Final LAS range

-730 to 365Raw score range

Jul 1, 2020Parameter tables date

337.97Example PT (days)

345.04Example WLi (days)

Trek Health ingests and normalizes Transparency in Coverage data and payer policy updates to give provider organizations a clear view of how commercial reimbursement behaves across markets, payers, and services. Our platform transforms raw payer disclosures into structured intelligence that supports contract evaluation, payer negotiations, and service line strategy. By combining market benchmarks with ongoing policy visibility, Trek helps teams identify variability, risk, and opportunity in commercial reimbursement. The result is faster insight, stronger negotiating positions, and more informed financial decisions.

LAS calculation steps (example)

Calculation steps and example values for LAS computation

Step 4: Calculate post-transplant survival measure: Compute post-transplant survival measure by calculating STX,i(t) at each timepoint using the baseline post-transplant survival probabilities (STX,0(t)) from Appendix 2 and the candidate-specific exponentiated linear predictor; then sum these values across the first post-transplant year to obtain PTi (∑STX = PT).

See Appendix 2 for baseline STX,0(t) values; compute STX,i(t) = STX,0(t) ^ (exponent multiplier) as shown in the worked example for Candidate Z.

Step 5: Calculate raw allocation score: Calculate the raw allocation score for candidate i as Raw scorei = PTi - 2 * WLi (where PTi is the summed post‑transplant survival measure and WLi is the summed waiting‑list survival measure).

Example given: PTi = 337.9676 and WLi = 345.0430 yielding Raw scorei = 337.9676 - 2*345.0430 = -352.1184.

Step 6: Normalize raw allocation score: Normalize the raw allocation score to obtain the final Lung Allocation Score (LAS) on a 0–100 scale using the referenced normalization formula.

Normalization formula is referenced in the document but the explicit formula text is not decoded in the excerpt; the normalization step converts the raw score to the 0–100 LAS scale.

The provided excerpt does not state any explicit coverage exclusions. It is a technical appendix focused on the method for computing the Lung Allocation Score (LAS), parameter estimates, and baseline survival probabilities; it cautions that the rounded values shown are for explanatory purposes and that the full, high-precision parameters and survival tables are maintained in the referenced policy documents (Policy 10.1.F and 10.5).

The normalization step (conversion of the raw allocation score to the 0–100 LAS) is referenced but the explicit normalization formula is not shown in this excerpt. The appendix notes that rounded parameters are for explanation only and that the precise parameter and survival values used in the official algorithm are available in the main policy documents.

Clinical Inputs & Coding-related Parameters

inv-04: Six-minute walk distance — model term and post-transplant parameter (0.0005*(1200 - distance), feet)

Model term (post-transplant)α for six-minute walk distance = 0.0005*(1200 - six-minute walk distance) — distance in feet

Variable measuredSix-minute walk distance obtained while candidate receives supplemental oxygen to maintain ≥88% saturation

UnitsFeet (used directly in α formula)

Usage noteα term applied in exponentiated linear predictor to adjust baseline post-transplant survival at each day

inv-05: Raw score range and normalization (raw -730 to 365; LAS = 100*(Raw + 730)/1095)

Raw score rangeRaw allocation score ranges from -730 to 365

Normalization formulaLAS = 100*(Raw score + 730)/1095

Post-normalization rangeFinal LAS ranges 0–100

inv-06: Six-minute walk distance influence — beta and alpha coefficient usage examples

Waiting-list β exampleβ for six-minute walk distance in waiting-list model = -0.0845 per 100 ft (β * six-minute walk/100)

Post-transplant α exampleα for six-minute walk distance in post-transplant model = 0.0005*(1200 - six-minute walk distance)

How coefficients are usedCompute exponent as sum(αj*Yj); exponentiate and apply to baseline survival at each time point (STX,0(t) * e^{sum}).

inv-07: Example numeric threshold used in raw score formula (Raw scorei = PTi - 2*WLi)

Raw score formula example componentRaw scorei = PTi - 2*WLi (multiplication factor 2 applied to WLi)

Worked numeric exampleExample: PTi = 337.9676, WLi = 345.0430 → Raw scorei = 337.9676 - 2*345.0430 = -352.1184

InterpretationThe factor 2 weights waiting-list urgency twice when computing raw allocation score

inv-08: Time (days) points referenced for survival tables (examples: 61, 122, 183, 244, 305, 366)

Example day points in survival tablesDays explicitly listed include 61, 122, 183, 244, 305, 366 (and many intermediate days)

Table granularityAppendix provides baseline TX survival probabilities by day up to ~364 days

Use in calculationSTX,0(t) values at these day points are applied when computing daily post-transplant survival and summing to PTi

Provider Responsibilities & Authorization Notes

Prior Authorization

Prior Authorization Not Specified

Prior authorization for lung transplant: This source excerpt does not specify payer prior authorization requirements for lung transplant. Clinicians should verify Blue Cross Blue Shield - Wisconsin prior authorization rules separately; the guide focuses on LAS calculation and not on coverage or authorization.

No payer prior authorization rules are stated in the excerpt.
Contact transplant center or payer for precise authorization requirements.

Note

Authorization Guidance Absent

Prior authorization (general): The document is a technical calculation guide and does not include operational prior authorization or denial triggers. Providers must not assume authorization guidance from this appendix.

This appendix contains calculation steps and baseline survival tables, not payer rules.
Any authorization determinations must come from the member's Blue Cross Blue Shield - Wisconsin policy or the transplant center's administrative processes.

Documentation Required

Data Completeness Required for LAS Calculation

Provider action — data completeness for LAS calculation: To compute an accurate Lung Allocation Score providers must supply complete, accurate clinical variables used in the LAS algorithm (examples: age, diagnosis, labs such as creatinine and bilirubin, BMI, hemodynamics, functional measures, oxygen requirement, pCO2, six-minute walk distance). Missing values may be substituted with defaults (normal or least-beneficial) which can materially change the LAS.

Ensure collection and documentation of: age, diagnosis, height/weight (for BMI), creatinine, bilirubin (+ change), cardiac index, CVP, continuous mechanical ventilation status, diabetes status, FVC% predicted, functional status, oxygen flow at rest, pCO2 (+ change), PA systolic pressure, six-minute walk distance.
If characteristics are missing the algorithm uses default values (either normal or least-beneficial) — document any substituted values.
Incomplete or incorrect data can prevent correct LAS computation and affect priority.

Note

Appendix Focus — Calculations and Baseline Survival Only

Appendix content summary — no step therapy or authorization rules: This appendix provides stepwise computational instructions for LAS and baseline post-transplant survival probabilities at specified days; it does not contain step therapy rules, utilization management criteria, or explicit coverage/denial triggers.

Contains calculation steps (steps 1–6) and baseline post-transplant survival probability tables (Appendix 2).
No step therapy, quantity limits, or payer denial criteria are present in this appendix.
Providers should use the baseline survival values and parameter estimates when computing LAS but refer to payer policy for coverage decisions.

Purpose & Overview of LAS

The Lung Allocation Score (LAS) is designed to prioritize lung transplant candidates by combining two components: a measure of waitlist urgency (expected survival on the waiting list over the next year) and a measure of expected post‑transplant survival during the first year. The scoring method computes candidate‑specific survival probabilities from parameter estimates and baseline survival curves, converts those into area‑under‑curve measures (WLi for waiting list and PTi for post‑transplant), forms a raw allocation score (for example, Raw scorei = PTi − 2*WLi in the worked example), and then normalizes that raw score to produce the final LAS used for prioritization.

Key Terms

inv-26: Waitlist urgency definition

DefinitionWaitlist urgency (WLi) = area under the waiting-list survival probability curve during the next year (number of days expected alive on the waiting list over 1 year)

RangeTheoretical range approximately 0 to 365 days

Calculation methodComputed as daily sum (rectangles width = 1 day, height = SWL,i(t)) using baseline WL survival adjusted by candidate characteristics

inv-27: Post-transplant survival definition

DefinitionPost-transplant survival (PTi) = area under the post-transplant survival probability curve during the first post-transplant year (sum of STX,i(t) across days)

RangeTheoretical range approximately 0 to 365 days

ComputationCompute STX,i(t) by exponentiating sum of α*Y and applying to baseline STX,0(t) at each day, then sum daily probabilities to obtain PTi

inv-28: WLi / PTi — definitions and units (days)

WLi (waiting-list measure)Area under waiting-list survival curve over 1 year, expressed in days alive expected during next year

PTi (post-transplant measure)Area under post-transplant survival curve over first post-transplant year, expressed in days

UnitsBoth WLi and PTi are measured in days (width of rectangles = 1 day) and range 0–365

inv-29: Raw allocation score — composite numeric value range and role

What it isRaw allocation score is a composite numeric value combining post-transplant benefit and waiting-list urgency (Raw scorei = PTi - 2*WLi)

Pre-normalization rangeRanges from -730 to 365

RoleServes as the basis for normalization to the Lung Allocation Score (LAS) 0–100

inv-30: Lung Allocation Score (LAS) — normalized 0–100 calculation

DefinitionLung Allocation Score (LAS) is the normalized final allocation score scaled to 0–100

Normalization formulaLAS = 100*(Raw scorei + 730)/1095

Scale endpointsRaw score -730 maps to LAS 0; raw score 365 maps to LAS 100

inv-31: Raw allocation score formula (Raw scorei = PTi - 2*WLi) and normalization to LAS

Raw score formulaRaw scorei = PTi - 2*WLi (applies candidate PTi and WLi measures)

Normalization stepAfter computing Raw scorei, normalize using LAS = 100*(Raw scorei + 730)/1095 to obtain final LAS 0–100

Worked exampleExample raw score: 337.9676 - 2*345.0430 = -352.1184 → then normalized to LAS per formula

inv-32: Baseline post-transplant survival probability at specified time (day indexed)

Baseline TX survivalAppendix 2 provides baseline post-transplant survival probabilities STX,0(t) by day (e.g., STX,0(0)=0.998946)

Use in modelSTX,0(t) values are multiplied by exponentiated linear predictor for candidate to compute STX,i(t) each day

Table coverageProbabilities listed for indexed rows and days up to ~364 days (daily entries in Appendix 2)

Model Inputs & Candidate Scoring Inputs

Inputs for LAS models — candidate clinical variables

Candidate clinical variables used in LAS models (waiting list and post-transplant) as listed in parameter tables:

Characteristic inputs: Age at offer/transplant; diagnosis group and detailed diagnosis flags (groups A–D and specified conditions such as bronchiectasis, Eisenmenger, LAM, obliterative bronchiolitis, pulmonary fibrosis, sarcoidosis with/without elevated PA pressure); bilirubin and bilirubin increase indicator; body mass index (BMI); cardiac index; central venous pressure (CVP); continuous mechanical ventilation status; creatinine and creatinine increase indicators; diabetes status; functional status (ADL assistance); oxygen requirement (L/min) needed to maintain ≥88% saturation; pCO2 and pCO2 increase indicator; pulmonary artery systolic pressure; six-minute walk distance (feet) performed on required supplemental oxygen; FVC % predicted; and other diagnosis-specific variables as specified in Tables 1 and 2.

These characteristics are entered into the waiting‑list and post‑transplant linear predictors using the β and α parameter estimates in Tables 1 and 2.

Inputs for LAS model — example Candidate Z characteristics

Candidate characteristics required for LAS component calculations (example values provided for Candidate Z).

Required clinical candidate inputs: Age at offer/transplant (example: 51 years for Candidate Z); bilirubin (mg/dL) and bilirubin‑increase indicator; height/weight (BMI) (example: BMI 25.0928 for Candidate Z); cardiac index (example: 2 L/min/m2 for Candidate Z); central venous pressure (CVP); continuous mechanical ventilation status; creatinine (mg/dL) and creatinine increase indicators (example: creatinine 1.0 mg/dL for Candidate Z); diabetes status; diagnosis group flags and detailed diagnosis flags (per Tables 1 and 2); FVC % predicted; functional status (example: requires some assistance for Candidate Z); oxygen requirement in L/min at rest to maintain ≥88% saturation (example: 4 L/min for Candidate Z); pCO2 and pCO2 increase indicators (example pCO2 contribution used for Candidate Z); pulmonary artery systolic pressure; and six‑minute walk distance in feet while receiving required supplemental oxygen (example: 800 ft for Candidate Z).

These values are multiplied by the corresponding β (waiting‑list) or α (post‑transplant) coefficients to form the exponent in the survival probability calculations (see worked exponent calculations for Candidate Z).

Inputs for LAS candidate scoring — baseline survival tables

Numerical survival tables used to score candidates

Use baseline WL survival table: Use Appendix 1 baseline waiting‑list (WL) survival probabilities by indexed category and timepoint when calculating SWL,i(t) and summing to obtain WLi (area under the waiting‑list survival curve over 1 year).

Appendix 1 provides WL survival probabilities for multiple indexed rows and days (sample entries include times at day 61, 122, 183, 244, 305, etc.).

Use baseline post-transplant survival table: Use Appendix 2 baseline post‑transplant (TX/STX,0(t)) survival probabilities by indexed category and day to compute STX,i(t) (apply the candidate‑specific exponent) and sum across days to obtain PTi.

Appendix 2 lists baseline TX survival values across days (examples for index 0: day 0 → 0.998946; day 305 → 0.947360) used in the worked example for Candidate Z.

Operational Requirements to Compute LAS

Documentation Required

Missing values are replaced with specified defaults

When candidate characteristics required for computation are missing, the algorithm uses default values; providers should be aware that defaults are either normal values or the least-beneficial values which affect the LAS.

Default values may be normal (healthy) or least‑beneficial (min/max) depending on the characteristic.

Documentation Required

Reference baseline WL and TX survival tables for computation

The LAS computation requires both baseline waiting‑list survival tables (Appendix 1) and baseline post‑transplant survival tables (Appendix 2); providers must reference these tables to compute WLi and PTi.

Use Appendix 1 WL survival probabilities to compute SWL,i(t) and sum to obtain WLi.
Use Appendix 2 TX survival probabilities to compute STX,i(t) and sum to obtain PTi.

Documentation Required

Both Appendix 1 and Appendix 2 are required inputs

Computation depends on both Appendix 1 (waiting‑list baseline survival) and Appendix 2 (post‑transplant baseline survival) as referenced in the worked example and must be applied when deriving candidate survival measures.

Documentation Required

Compute candidate-specific PT and WL measures before LAS normalization

Compute candidate‑specific post‑transplant (STX,i(t)) and waiting‑list (SWL,i(t)) survival probabilities using the provided parameter estimates and baseline tables, then sum across timepoints to obtain PTi and WLi prior to normalizing the raw score to LAS.

Step 4: compute STX,i(t) at each time point using baseline values and exponentiated linear predictor.
Step 5: sum STX,i(t) to PTi and sum SWL,i(t) to WLi, then compute Raw scorei = PTi - 2*WLi.

Post-Transplant Survival Modeling Inputs

inv-41: Survival probability modeling for first-year post-transplant — STX,i(t) computed from baseline and α coefficients

Model formSTX,i(t) is computed by exponentiating the sum of αj*Yj and applying that factor to baseline STX,0(t) at each day

Computation steps(i) compute sum(α*Y) (ii) exponentiate (iii) apply to baseline survival: STX,i(t) = STX,0(t)^{e^{sum}} (document shows STX,0(t) * e^{sum} formulation for application)

Result usedDaily STX,i(t) values are summed across days to obtain PTi

inv-42: Post-transplant survival estimation for LAS — exponentiated linear predictor with α coefficients and baseline survival

EstimatorPost-transplant survival for LAS is computed by exponentiating the linear predictor (e^{ΣαY}) and applying to baseline STX,0(t) to obtain STX,i(t)

Example numeric exponentExample exponent e^{0.7124} = 2.03888 used to scale baseline post-transplant survival for Candidate Z

ApplicationSTX,i(t) = STX,0(t) * 2.03888 in the worked example, then summed to PTi

inv-43: post-transplant survival input data — appendix provides probabilities; no coverage duration rules in excerpts

Source of input dataAppendix 2 contains baseline post-transplant (TX) survival probabilities by indexed rows and days used as input for LAS calculations

No coverage duration rules in excerptAppendix supplies numerical probabilities; the excerpts do not state payer coverage durations or limits

Provider requirementProviders must use these appendix values when computing STX,i(t) and PTi for LAS

inv-44: Baseline post-transplant survival probabilities (appendix table) — indexed rows and days for use in LAS calculation

Table contentsAppendix 2 lists baseline post-transplant (TX) survival probabilities STX,0(t) for indexed rows and for days (examples: day 0 STX,0=0.998946; day 305 ≈0.947360)

Day coverageProbabilities provided across many day points up to ~364 days; used to compute daily STX,i(t) and sum to PTi

Example entriesSample entries shown: STX,0(0)=0.998946; STX,0(61)=0.978452; STX,0(122)=0.968956; STX,0(183)=0.960075; STX,0(244)=0.953850; STX,0(305)=0.947360

Policy Summary

PayerBlue Cross Blue Shield - Wisconsin

PolicyLung Allocation Score (LAS) calculation guide

Policy CodePolicy N/A

Change TypeInformational — no coverage or authorization changes in excerpt

Effective DateN/A

Next Review DateN/A

Key ActionProvide complete candidate clinical variables and required survival-table inputs so the LAS can be computed accurately.

SourceLink

On This Page

OpenPayer

Lung Allocation Score (LAS) calculation guide

LAS Calculation & Coverage Context

Clinical Inputs & Coding-related Parameters

Provider Responsibilities & Authorization Notes

Purpose & Overview of LAS

Key Terms

Model Inputs & Candidate Scoring Inputs

Operational Requirements to Compute LAS

Transplant Center Notes

Post-Transplant Survival Modeling Inputs