Early every year, countless Americans embark on a new fitness regime. They go for a physical and maybe for a blood test to measure cholesterol levels. After a clean bill of health, they might train to run a 10K, a marathon or even an Iron man.

But what if those tests do not provide a complete picture of your health? What if you are on the verge of a heart attack and have no idea?

Before 30, when the human body is at its peak, it can take the strain of being pushed to the limit. As we age, however, cellular changes and the expression of genetic predispositions can dramatically alter our health. Conventional medical tests are too superficial, too limited, and too generic to diagnose all health problems that may be looming.

That’s why people who present as healthy and are in the so-called “normal range” on cholesterol tests have dropped dead of heart attacks, even as they appear fit enough to run marathons.

To get a sense of the complexity involved, look at the results from a recent study on a promising new cholesterol drug, evacetrapib. It was found to lower the “bad” LDL cholesterol in patients by as much as statins do, and doubled “good” HDL cholesterol, giving cardiologists great hope of a new weapon against heart disease. Only it surprised everyone when its use in a human study of 12,0000 patients did not improve users’ heart health at all. In fact, one more person in the study had a heart attack than in a placebo group. The drugmaker, Eli Lilly, stopped the study.

On Sunday, cardiologists and other specialists were able to access the trial data for the first time, and were stunned that the treatment was not effective, despite the changes in the standard cholesterol readings.

Perhaps the researchers shouldn’t have been so surprised. There’s a growing body of pharmacogenetics research to support the fact that individuals metabolize drugs differently. In fact, Crestor, a top-grossing statin, has shown to benefit only one in 20 individuals prescribed the drug.

What a reminder that human physiology is complex, and that the simple “bad” and “good” cholesterol readings do not provide enough depth to truly understand your risks.

The underlying principle is simple: conventional medical tests cannot always reveal underlying problems. We see this regularly in my precision medicine practice, where we often reveal medical conditions that (a) standard health assessments cannot reveal, and/or (b) are far more serious than the chief complaint that brings a client to us.

One such client came in complaining that he could no longer maintain his usual workout pace at the gym. We found that, despite his muscular physique and eight-pack abs, he was pre-diabetic with high cholesterol.

To say that our client was “surprised” is a substantial understatement. A health-conscious surgeon himself whose worst vice was a glass of red wine once a week, his standard cholesterol results had shown optimal levels for the typical markers — total cholesterol, triglycerides, HDL, LDL. In fact, his primary physician had given him a clean bill of health and permission to go out for a celebratory steak dinner.

Yet a more precise blood lipid panel revealed a bill of health that was not entirely “clean.” A lipoprotein subfraction analysis revealed his LDL small and medium particles were dangerously high and that his HDL particles were not the protective type. His fibrinogen antigens showed elevated levels of inflammation, and a mutation in the MTHFR gene compromised his ability to metabolize essential B vitamins, and put him at risk for deep vein thrombosis, blood clots and an early heart attack.

Another client came to my office with vague and non-urgent complaints of low libido and sleeplessness. Our analysis found that despite her lean, relatively cheerful, and attractive presentation, she had osteoporosis, florid diabetes, and was at risk of a heart attack.

The prescriptive medicine practiced by the majority of American doctors has, sadly, major shortcomings. The old-school approach employs standards based on norms that can be meaningless, because — and I cannot stress this more strongly — each individual is unique. Generic testing and superficial metrics are insufficient with respect to many variables which lead to disease: they simply do not delve deep enough to offer meaningful, personalized results.

Ideally, mainstream medicine would detect, predict, and reverse disease before problems are obvious. However, standard medical training doesn’t encourage ferreting out disease before it interferes with the patient’s quality of life. In fact, medical students are trained to wait until symptoms are evident. Extra tests are considered “fishing expeditions” — too costly and ineffective.

Whether this stems from the effort to control costs or the “if it’s not broken, don’t fix it” mentality, the result is a sicker society where too often we receive our diagnosis — a heart attack, stroke, diabetes — in the emergency room. Imagine instead if the ER’s function was dealing with accidents and injuries, rather than preventable, age-related disorders driven in part by lifestyle and genetics. Imagine the cost savings if each of us was as invested in maintaining our health as we are in maintaining our financial portfolios, and actively opposed to accepting that our health declines each time we blow out another birthday candle.

While conventional medicine detects flagrant disease that’s already erupted, precision medicine analyzes an individual’s health at the cellular level, over time, to spot trends and decline. People are unique, and require personalized testing in the context of metabolomics, hormones, personal and family history, lifestyle — sleep, stress, nutrition and exercise — and genomics to attain and sustain peak health for life.

The good news is that last year President Obama embraced personalized medicine with a $215 million initiative to advance research. The sooner America realizes the value of precision medicine, the better — approximately 787,000 people in the United States died from heart disease, stroke and other cardiovascular diseases in 2011, roughly one of every three U.S. deaths. Diseases can, and should, be detected years, even decades before overt symptoms. Yet, that rarely happens, and if by chance, there is evidence, individuals are mostly told that the doctor “will keep an eye on it.”

Under the watchful eye of conventional medicine, your first heart attack can kill you. Individuals like James Gandolfini and Tim Russert, not to mention the hundreds, maybe thousands of lesser known, including allegedly fit marathoners and athletes, fall into that category.

Florence Comite is an MD and Founder of ComiteMD