CSI Severity Classification Tiers
The Comprehensive Severity Index (CSI®) may be thought of as
a multi-tiered classification system that stratifies signs and symptoms of
disease for patients in multiple health care settings; successive tiers reflect
increased specificity.
The more than 2,100 CSI criteria are objective
clinical findings (not treatments) such as vital signs, laboratory values,
radiology findings, and physical findings derived from examination of multiple
body systems. Examples of physical
findings are: heart sounds, edema, pulse characteristics, dyspnea, adventitious
breath sounds, cyanosis, hematemesis, vomiting, dysuria, seizures, mental status,
sensation, and wound characteristics.
Some of CSI criteria apply to specific age groups only, e.g., neonates
or pediatrics. Other criteria are
applicable to all ages.
TIER 2 –
Association of signs and symptoms with each ICD-9-CM diagnostic code
The ICD-9-CM coding system contains over 19,000
diagnostic codes, which are used in clinical settings to indicate the existence of a disease. CSI aggregates similar ICD-9 codes into
groups and associates specific Tier 1 signs and symptoms with each group. This advances the specificity of CSI from a
generic sign and symptom level (Tier 1) to a disease-specific level (Tier
2). The over 19,000 ICD-9 codes are
grouped into about 2,700 CSI disease groups.
The CSI disease group for pneumonia illustrates the association between ICD-9 code and CSI
signs and symptoms. Criteria associated with the pneumonia ICD-9 codes 480-486
include temperature, pulse, blood pressure, Glasgow coma scale, cyanosis,
chills, sputum/hemoptysis, mental status, dyspnea, rales, breath sounds,
stridor, fremitus, chest x-ray findings, EKG rhythm, arterial blood gasses,
white blood cell counts, and bands.
Some CSI criteria are associated with multiple
disease groupings, of course. However,
some CSI criteria are specific to just a few diseases and thus, are associated
only with their ICD-9 codes. For
example, pulsus paradoxus is relevant to myocarditis, pericarditis,
endocarditis, and aneurysm of the heart, but not to most other diseases.
TIER 3 –
Assignment of weights to the CSI criteria associated with each disease group
In Tier 3, all of the CSI criteria associated with a
specific disease are arranged into a severity
matrix. Each severity matrix contains four columns, one each for: normal to
mild symptoms, moderate symptoms, severe symptoms, and catastrophic or
life-threatening symptoms with likelihood of organ failure. The severity matrix
converts a patient's set of signs and symptoms for a given disease into a list of weights––1, 2, 3, or
4––depending on the degree of severity of each sign or symptom for a particular
patient and disease. The CSI logic uses
these weights to produce a severity score for each of a patient’s diseases.
For example, some of the severity pneumonia criteria
are weighted as follows:
·
Sputum:
frank hemoptysis is weighted as 3, purulent sputum is weighted as 2, and white,
thin, or yellow sputum is weighted as 1.
·
Dyspnea:
apnea is weighted as 4, dyspnea at rest is weighted as 3, and dyspnea on
exertion is weighted as 2.
·
White
blood cell counts are weighted according to their value: ³ 100 K is weighted as 4, 20.0-99.9 K is
weighted as 3, 11.1-20.0 K is weighted as 2, and £11.0 K is weighted as 1.
TIER 4 –
Combine disease-specific severity scores for each of a patient’s diseases to
obtain an overall patient severity score
In Tier 4 CSI combines the severity scores obtained
in Tier 3 for each separate disease to produce an overall patient severity
score. This overall severity score is
presented on a categorical scale of 1 to 4, as well as on a continuous scale
with non-negative integer values that are not subject to any preset maximum
limit. Higher numbers mean that
patients are more severely ill.
The Tier 4 algorithms combine the severity scores
for all of a patient’s diseases using disease-specific rules that reflect the interaction
of the diagnoses. CSI's logic takes
into account the interactions of the
diseases that are present, their severity
scores, and the clinical
relationships of the diseases, along with the patient's age and the setting
of care.