In what promises to be an eye-opener for many doctors and patients who routinely depend on cholesterol testing, a new study has found that the standard formula used for decades to calculate low-density lipoprotein (LDL) cholesterol levels is often inaccurate. Of most concern, the researchers say, is their finding that the widely used formula underestimates LDL where accuracy matters most — in the range considered desirable for high-risk patients.