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Dr. Paul Grayburn provides a brief review on CAC score interpretation in the NEJM.  He presents the case scenario of a patient whose score increased from 39 to 119 over a 5-year period.

Grayburn toes the party line on the subject:  “limited value.”

As usual, he presents risk assessment as if it is a totally objective variable.  This is at odds with his statement that CAC scoring “is useful in encouraging medical compliance.”  The patient in question, whom Grayburn considered to be at low risk, became anxious about the increased score despite being on rosuvastatin for the prior 3 years.  Someone then made the decision to do a treadmill test, quadruple the statin dose (his baseline LDL was 86), and add aspirin even though there are “no prospective randomized, controlled trials demonstrating that an abnormal CAC score influences treatment decisions.”

Another puzzle in this editorial is Grayburn’s comment about the MESA score, which combines CAC results and clinical variables:

Interestingly, had this patient’s total cholesterol level been only 10 mg per deciliter higher, his MESA risk score would have increased from 12% to 20% with a CAC score of 119 — a disparity that highlights the need to consider CAC scores only in the context of other clinical risk factors, particularly cholesterol levels and blood pressure.

By combining the CAC score with Framingham, the MESA score projects clinical risk as a function of “arterial age.”  When CAC scores are even mildly elevated (such as 119), the Framingham risk estimate jumps dramatically.

But as Rayburn mentions earlier in the editorial, “According to the guidelines, CAC scoring was not needed, because this man’s predicted coronary event rate was low.”  Yet his Framingham risk would also have been low if the total cholesterol was 10 points higher (the Framingham score is not nearly as sensitive as the MESA score to changes  total cholesterol levels).  The benefit of calcium scans is precisely to identify patients who would otherwise fall under the radar.

CAC score will and should influence behavior.  The decision to order a calcium scan should be left to the doctor and the patient.

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