Traditionally, we are taught that laboratory tests have “normal ranges”, such as in haemoglobin or creatinine. However, this concept of “normal”, when applied in cholesterol measurement, often creates confusion amongst some clinicians and certainly in most patients.
An illustrative example would be that a relatively well-informed patient comes to you questioning the recommendation of starting lipid-lowering medications when his LDL, total cholesterol and ratio are only just above the normal limits. “Doctor, why do I need statins, when my cholesterol is almost normal?” What is forgotten is that that patient might be a current smoker, who has poorly controlled Type II diabetes, hypertension and is physically inactive.
Therefore, this brings us to the concept of defining treatment threshold based on overall cardiovascular disease risk, rather than an absolute cholesterol level (or BP level similarly) in isolation.
In primary prevention, lipid-lowering via statins reduces cardiovascular events. The relative risk reduction (RRR) is pretty uniform regardless of the pre-treatment lipid profile. In other words, someone who has an LDL of 4.0 derives a similar RRR from statin therapy as someone who has an LDL of 2.0.
As a result, the absolute benefit of lipid-lowering is defined by the overall risk of the individual patient based on all the cardiovascular risk factors, and not just a baseline pre-treatment lipid level. Treatment threshold, therefore, should be defined by the overall cardiovascular risk, rather than solely on lipid level itself.
In the field of hypertension, the latest ACC/AHA 2017 hypertension guideline also recognises the need to tailor treatment decisions based on overall cardiovascular risk. Please refer to a separate blog article about the latest hypertension guidelines. But in short, there are now two-tier treatment thresholds, based on the 10-year absolute cardiovascular risk: 130/80mmHg if high risk vs. 140/90mmHg otherwise.
Author: Dr Andrew To