Lung Allocation Score (LAS) calculation guide
Customize your policy alerts
Sign up for all Blue Cross Blue Shield - Wisconsin policy alerts
Know when Blue Cross Blue Shield - Wisconsin releases new policies or updates existing guidance.
Monitor payer policy activity
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.
No material clinical or coverage changes in this revision.
LAS Calculation & Coverage Context
LAS calculation steps (example)
Calculation steps and example values for LAS computation
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.
Example given: PTi = 337.9676 and WLi = 345.0430 yielding Raw scorei = 337.9676 - 2*345.0430 = -352.1184.
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
Provider Responsibilities & Authorization Notes
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.
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.
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.
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
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:
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).
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
Appendix 1 provides WL survival probabilities for multiple indexed rows and days (sample entries include times at day 61, 122, 183, 244, 305, etc.).
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
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.
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.
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.
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.
Transplant Center Notes
Contact transplant center for precise LAS for listed candidates
Center‑level instructions for obtaining a precise LAS for candidates currently listed are not provided in this excerpt; the document advises contacting the transplant center for exact scores.
Post-Transplant Survival Modeling Inputs
OpenPayer is powered by Trek Health's payer performance platform. Trek continuously ingests, validates, and normalizes Transparency in Coverage data alongside payer policies and other commercial payer data to create a structured payer intelligence foundation. OpenPayer uses this foundation to deliver personalized search results, dynamically generated policy pages, and tailored policy monitoring based on each user's payers, specialties, billing codes, and areas of interest. The same intelligence powers broader payer performance workflows, including reimbursement benchmarking, contract evaluation, payer negotiations, and financial decision-making.