Accuracy and precision of HDL cholesterol measurements using an office chemistry analyzer

Journal of Family Practice, April, 1991 by Patrick J. Fahey, John A. Lott, Georgia M. Peet, Lawrence E. Crowley

Background. A physician can obtain a patient's complete lipoprotein profile at the time of the office visit including assays of the total serum cholesterol, high-density lipoprotein cholesterol (HDL-C), and fasting triglyceride concentrations, and then calculate the low-density lipoprotein cholesterol (LDL-C). Until recently, this was not possible. Instruments are currently available that provide reliable rapid total serum cholesterol and fasting triglyceride measurements.

Methods. This study evaluated the accuracy and precision of a recently developed analytical method for the rapid measurement of HDL-C (Seralyzer Cholesterol System) as compared with a reference clinical laboratory method (Kodak Ektachem 700 XR). Blood specimens were taken from 90 participants and were analyzed in duplicate for HDL-C concentrations and total cholesterol using the Seralyzer and a standard Ektachem 700 XR.

Results. Nearly all (98.9%) of the initial Seralyzer HDL-C measures were within [ or -] 0.08 mmol/L ([ or -] 3 mg/dL) of the duplicate Seralyzer values. Most (98.3%) of the Seralyzer HDL-C results were within [ or -]0.16 mmol/L ([ or -]6 mg/dL) of the Kodak HDL-C values.

Conclusions. The Seralyzer HDL-C test provides a reliable and accurate measure of the HDL-C concentrtaion.

Key words. Lipoproteins, HDL cholesterol; diagnosis; laboratory. J Fam pract 1991; 32;382-386.

The National Cholesterol Education Program (NCEP) was inaugarated in 1985 by the National Heart, Lung, and Blood Institute of the National Institutes of Health in response, at least in part, to the findings of several major epidemiological and clinical studies that presented strong evidence of a causal link between high serum cholesterol concentrations and coronary artery disease. [1-5] three major classes of lipoprotein-bound cholesterol play a part in the development of coronary artery disease. There is a direct relationship between low-density lipoprotein cholesterol (LDL-C) and the risk of developing coronary artery disease, and an inverse relationship between high-density lipoprotein cholesterol (HDL-C) and the risk of developing coronary artery disease. [1,4-6] In addition to these causal relationships, the Lipid Research Clinics Coronary Primary Prevention Trial [7,8] recently provided evidence that lowering the LDL-C also lowers the incidence of coronary artery disease. The drug cholestyramine and moderate cholesterol-lowering diet reduced both the level of serum LDL-C concentration and the incidence of coronary artery disease.

Since the inception of the NCEP, great progress has been made in the detection, evaluation, and treatment of hypercholesterolemia. The 1988 NCEP report suggested two approaches to lower blood-cholesterol concentrations. [9] The patient-based approach seeks to identify high-risk persons in need of intensive intervention efforts. NCEP recommended that all adults over 20 years of age have their total serum cholesterol measured at least every 5 years and that those with borderline-high (5.17 to 6.18 mmol/L, or 200 to 239 mg/dL) or high ([is greater than or equal to]6.20 mmol/L, or [is greater than or equal to]240 mg/dL) serum cholesterol levels have their cholesterol level measured more often. Persons with a high serum cholesterol level or individuals with borderline-high serum cholesterol levels and two other risk factors for developing coronary artery disease, such as hypertension and smoking, are advised to have a lipoprotein analysis done to provide a more precise estimate of their degree of risk. Such an analysis provides the fasting concentrations of total cholesterol, high-density lipoprotein cholesterol, and total triglycerides. Using this information, the LDL-C can be calculated in mmol/L (ie, SI units): [9]

LDL-C = total cholesterol - HDL-C

-fasting triglyceride/2.18

This can also be calculated in mg/dL:

LDL-C = total cholesterol - HDL-C

- fasting triglyceride/5

The above equation is valid for triglycerides up to 4.52 mmol/L (400 mg/dL). The NCEP considers a low level of HDL-C (<0.92 mmol/L, or <35 mg/dL) to be a risk factor for coronary artery disease.

The total serum cholesterol concentration is a good initial measure for identifying high-risk individuals. Currently there are ast, accurate in-office tests available that can determine the total serum cholesterol and allow the physician to make some decisions about further testing and treatment while the patient is still in the office. Until recently, fast, accurate, in-office tests for LDL-C or HDL-C concentrations have not been available. If the total serum cholesterol, HDL-C, and fasting triglyceride concentrations are all determined at the time of the office visit, the LDL-C concentration can also be calculated at that time using the above equation. With this information in hand, the physician can counsel the patient concerning his or her cholesterol profile at the time of the office visit and make arrangements for follow-up confirming tests if they are warranted. This rapid feedback avoids the problems physicians encounter when they attempt to contact patients with their final recommendations at a later date. A rapid in-office test for determining total cholesterol and HDL-C concentrations provides this immediate feedback.