Severity Modifier Tables: PROMIS® and Neuro-QoL

Assigning a G-code severity modifier (level of impairment) to a patient relies on clinical judgment. The tables below can inform decision-making by providing detailed information about PROMIS and Neuro-QoL score ranges associated with individual G-code severity modifiers.

Note: A higher PROMIS or Neuro-QoL T-score represents more of the concept being measured. For negatively-worded concepts like fatigue or pain interference, a T-score of 60 is one standard deviation worse than average. By comparison, a fatigue T-score of 40 is one standard deviation better than average. The reverse is true for positively worded concepts like physical function (i.e., higher scores indicate better function).

The tables below provide detailed information about PROMIS and Neuro-QoL score ranges associated with individual G-code severity modifiers.

Severity Modifier

% Impaired, Limited, or Restricted

PROMIS Physical Function v2.0 T-scores* PROMIS Upper Extremity Function v2.0 T-scores**
CH 0% 60.0 or higher 55.0 or higher
CI 1% to 19% 50.0 – 59.9 50.0 – 54.9
CJ 20% to 39% 45.0 – 49.9 40.0 – 49.9
CK 40% to 59% 40.1 – 44.9 35.1 – 39.9
CL 60% to 79% 35.1 – 40.0 30.1 – 35.0
CM 80% to 99% 20.1 – 35.0 20.1 – 30.0
CN 100% 20.0 or lower 20.0 or lower

Note: Higher PROMIS Scores = Better Physical Function

Severity Modifier

% Impaired, Limited, or Restricted

Neuro-QoL Lower Extremity Function - Mobility v1.0 T-scores Neuro-QoL Upper Extremity Function - Fine Motor, ADL v1.0 T-scores
CH 0% 62.4 and higher 57.0 and higher
CI 1% to 19% 51.0 – 62.3 50.1 – 56.9
CJ 20% to 39% 45.2 – 50.9 41.3 – 50.0
CK 40% to 59% 40.6 – 45.1 36.6 – 41.2
CL 60% to 79% 35.9 – 40.5 31.7 – 36.5
CM 80% to 99% 14.0 – 35.8 11.5 – 31.6
CN 100% 13.9 and lower 11.4 and lower

Note: Higher PROMIS Scores = Better Physical Function

Severity Modifier

% Impaired, Limited, or Restricted

PROMIS Pain Interference v1.1 T-scores* PROMIS Fatigue v1.0 T-scores**
CH 0% 40.0 or lower
30.0 or lower
CI 1% to 19% 40.1 – 50.0 30.1 – 45.0
CJ 20% to 39% 50.1 – 55.0 45.1 – 55.0
CK 40% to 59% 55.1 – 62.4 55.1 – 62.4
CL 60% to 79% 62.5 – 69.9 62.5 – 69.9
CM 80% to 99% 70.0 – 79.9 70.0 – 79.9
CN 100% 80.0 or higher 80.0 or higher

Note: Higher PROMIS Scores = More Pain Interference or Fatigue

Distributional methods were used to map Neuro-QoL and PROMIS T-scores to G-code modifiers. Distributional methods recognize that the possible range of test scores do not reflect the scores people actually receive. They also prevent complications that occur when score ranges vary based on the version of a test that is administered (e.g., a 4-item short form vs. a computer adaptive test).

Neuro-QoL Mapping Methods
Neuro-QoL scores were mapped to G-code modifiers using percentiles based on data obtained from the adult general population. For example, on Neuro-QoL Upper Extremity Function - Fine Motor, ADL measures, 20% of people (20th percentile) in the general population received a score of 31.7. Because lower scores on this measure indicate more impairment, a score less than 31.7 is associated with modifier CM (11.5 – 31.6) or CN (11.4 or lower), indicating more than 80% impaired.

PROMIS Mapping Methods
The distributional approach used for PROMIS reviewed the range of possible T-scores on an exemplar form. For PROMIS, this was the computer adaptive test. Then, that range of possible scores was divided into groups for each G-code severity modifier based on the theoretical distribution of scores and other information known about the measure. For example, a T-score of 50 on PROMIS Physical Function means that approximately half of people in the general population do better than it, and half do worse. This does not indicate 50% impairment, but it also does not indicate 0% impairment. Using clinical judgement and knowing some information about the range of possible measure scores, a PROMIS Physical Function T-score of 50 reflects approximately 1% to 19% of impairment and should therefore be associated with a CI modifier.

Other Mapping Methods
Another method is sometimes used for self-report measures that have a score range of 0-100. The percent impairment is set to match the score. For example, the Neck Disability Index generates scores ranging from 0 to 100. A score of 50, for example, is then associated with CK (the modifier used for 40% to 59% impaired, limited, or restricted). As PROMIS and Neuro-QoL utilize T-scores, in which the mean of the referenced group (usually the general population) is set to be 50, their possible score range is not necessarily fixed to be 0 to 100. Therefore, this method is not suitable to the PROMIS and Neuro-QoL measures.

With all of these approaches, a clinician must use all available evidence to choose the most appropriate G-code severity modifier. Scores from multiple tests can provide evidence for one or more different modifiers. Thus, anchoring final decisions clinically using all information about a patient is the most important final step in identifying the correct G-code severity modifier.