NELA & POSSUM Differences
The NELA Project Team have received queries as to why the NELA Risk number differs from P-Possum.
Below we provide an explanation of some of the greatest contributors to the difference.
These are:
1. ASA score - which is in NELA but not P-POSSUM.
2. Age - is modelled as a continuous variable in NELA and categorical in P-POSSUM and has a sizeable effect in NELA.
3. Gender - is included in NELA (not P-POSSUM).
4. The weight given to operative severity is very large in P-POSSUM, but less so in NELA. The latter only has a small boost in risk for the Major+ category (ie all emergency laparotomies are considered high risk).
5. Serum creatinine is included in NELA, only urea is in P-POSSUM.
6. Haemoglobin is included in P-POSSUM, not NELA.
7. Probably the single biggest reason for the difference is the move away from categorisation of variables (as happens in P-POSSUM) and towards continuous variables in NELA - so a small difference in values will be reflected, whereas P-POSSUM variables must cross a threshold to be noticed.
