What is Risk scoring ?

Risk scoring is an instrument to assess both the relative risk as well as the absolute risk of developing Cardio-vascular disease and mortality in an individual. As told earlier, co-existence of multiple risk factors magnifies the risk of CAD in an exponential manner. This has given rise to the concept of comprehensive Cardio-vascular risk or total risk score, quantifying an individual's overall risk of developing CVD because of the confluence of risk factors. In risk scoring the weight age given to different risk factors are summed up to get the final score which in turn indicates the probability of the disease. There are different methods of risk scoring - some use mathematical model, some use charts and some use computer programmes. The risk factor variables used in calculation also differ among the various methods. However all of them give some idea about the relative and the absolute risk and help in taking a decision about the preventive measures and drug treatment.

Relative risk is the ratio of the likelihood of CAD developing in persons with and without a given risk factor or at a given intensity of a risk factor. Absolute risk is the probability of developing CAD in a finite period, e.g., within the next ten years. In a sense, relative risk reflects the rate at which a person is accruing absolute risk. Serum cholesterol data provide a good example of the difference between relative and absolute risk. A young person with high serum cholesterol level carries a low absolute risk for CAD but has a high relative risk compared with another young with a low serum cholesterol level. The hy percholesteroleinic young adult is unlikely to develop CAD in the next ten years, but his or her chances of having premature CAD in the long-term (e.g. before age 65) are high.
Long-term follow-up data from Framingham confirm this concept: cholesterol levels measured in young adulthood are inversely associated with life expectancy. Results from other studies also support the concept that a high relative risk in young adulthood is transformed into a high absolute risk in the long run. The goal for reducing elevated serum cholesterol in young adults thus is to retard atherogenesis throliglaout life, not to prevent myocardial infarction in the next decade. This is justifies efforts to detect elevated serum cholesterol in young audits advising lifestyle modification. There is a misconception on the part of some investigators t.hat absolute risk for CAD can be almost fully reversed by aggressive clothes raspy initiated after atherosclerosis has become advanced. Certainly redaction of serum cholesterol levels in patients with advanced atherosclerceticd disease does substantially reduce morbidity and mortality from CAD but the persistently high rate of coronary events even in those patients who receive cholesterol-lowering drugs reveals that risk cannot be fully reversed.

Risk scoling is essential for planning the line of management of a patient. The Framinghain risk scoring was the first such method - which took six variables to predict the 10 and 20 year risk of CAD. Framinghain risk scorch furnish two ways to estimate relative is one compares a given individual's estimated risk with the absolute risk of an individual at low risk, i.e., a person who is largely without risk factors. The other compares a given individual's estimated risk with the risk of an average person of the same age and sex. The latter ratio is commonly used, although it tends to underestimate the preventable component of coronary risk. A better way to assess the full potential for risk reduction, when introduced relatively early in life, is to compare estimated absolute risk with truly low risk. Total excess risk for an individual patient can be estimated by subtracting that person's absolute risk from the absolute risk of a person of the same age and sex who is at low risk. Absolute risk assessment charts are now included with many guidelines to enable clinicians (and their patients) rapidly to measure a patient's absolute risk of coronary heart disease or Cardio-vascular disease. The current Joint British chat and New Zealand chart are similar in concept, both having been strongly influenced by the 1994 Joint European societies' charts. Both incorporate the same age categories and risk factors, with blood pressure and the total cholesterol: high density lipoprotein cholesterolratio presented as continuous variables. While the New Zealand chat assesses five year risk of all Cardio-vascular disease in eight discrete categories, the Joint British chart assesses ten year risk of coronary heart disease in three risk bands. As well as risk, the New Zealand charts enable one to estimate the five year benefit of treatment, expressed as events prevented per I00 patients treated and as the number of patients needing treatment (NNT) for five years to prevent one event. The Sheffield tables, which were specifically designed to target lipid lowering therapy to patients at high absolute risk, simplify treatment decisioils by using a truncated risk factor set and by enabling estimation of risk above specified treatment cut off 1evel.s. Blood pressure levels are dichotomised, and only the most recent version of the tables include high density lipoprotein cholesterol. Like the Joint British charts, the Sheffield tables estimate the ten year risk of coronary heart disease.

All the risk charts mentioned above used risk prediction equations derived from the Framingham heart study. The Framingham risk score is widely used but it has certain limitations. Framingham equations can predict coronary risk with reasonable accuracy in white men and women in the Europe and USA. However, little is known about the charts' predictive validity in high risk groups such as South Asians, Polynesians, or African Americans. One must understand that the ethnic variations in the risk factor effect will influence the calculated risk in different ethnic groups. For the Indians, the cut-off point for cholesterol level, weight, waist hip ratio generally underestimate the risk of CAD and the threshold need to be lowered for risk estimation.

Most of the risk scoring algorithms focus on 5 year or 10 year absolute risks for coronary artery disease, and the underlying assumption is that intensity of prevention efforts should match the absolute risk of developing CAD. The emphasis on estimating the short time risk is because of various considerations including the benefit of identifying those patients who will gain most from drug therapy and also concern about cost-effectiveness and safety. While short-term risk assessment is helpful in a high-risk individual, it is also essential to identify the long time risk because even a single elevated risk factor can lead Lo significant risks for CVD in future years, In addition, clustering of even modestly elevated risk factors in young individuals has little effect on short-term risk, but can elevate longer-term risks for CVD substantially. It is therefore also important to estimate the long-term and lifetime risk for CVD.