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Identifying patients with hypercholesterolemia. More than one blood sample is needed
M Speechley1, S McNair, A Leffley
1Department of Physical Therapy, Faculty of Applied Health Sciences, University of Western Ontario, London.
Insights
Diagnosing hypercholesterolemia requires two total cholesterol (TC) blood samples for accuracy. A single TC test has a high misclassification rate, leading to unreliable diagnoses and treatment decisions.
Area of Science:
- Clinical Chemistry
- Preventive Cardiology
- Family Medicine
Background:
- Hypercholesterolemia is a significant risk factor for cardiovascular disease.
- Accurate diagnosis is crucial for timely intervention and management.
- Current diagnostic practices may rely on single measurements, potentially leading to misclassification.
Purpose of the Study:
- To compare the diagnostic accuracy of using one versus two blood samples for hypercholesterolemia.
- To evaluate the reliability of single total cholesterol (TC) measurements in classifying cholesterol risk categories.
Main Methods:
- A test-retest substudy within a randomized control trial involving 142 patients with moderate hypercholesterolemia.
- Two blood samples for TC level determination were collected from each participant at different times.
- Classification into normal, moderate, or high cholesterol risk categories was based on single and average TC values.
Main Results:
- The overall misclassification rate using a single TC level was 22.5%, with a high false-positive rate of 50% for those initially in the high-risk category.
- The false-negative rate was 3.5%.
- Misclassification rates were not significantly influenced by patient demographics, clinical factors, or fasting status.
Conclusions:
- Single total cholesterol measurements are unreliable for diagnosing hypercholesterolemia.
- Family physicians should utilize the average of two cholesterol readings, taken 1-8 weeks apart, for diagnostic and treatment decisions.
Objective:
To compare the use of one and two blood samples for diagnosing hypercholesterolemia
Design:
A test-retest substudy conducted as part of a randomized control trial designed to compare the effectiveness of different counseling strategies for lowering serum cholesterol, dietary fat, and dietary cholesterol in patients with moderate hypercholesterolemia.
Setting:
Thirty urban family practices.
Participants:
One hundred forty-two patients provided two blood samples for total cholesterol (TC) level determination at two different times (test results were being used as an eligibility criterion for enrollment in the main trial).
Main Outcome Measures:
Number of subjects correctly classified to cholesterol risk category (normal < 6.2 mmol/L; moderate 6.2 to 6.9 mmol/L; high > 6.9 mmol/L) on the basis of one TC value and on the average of two TC values.
Results:
Overall misclassification rate on initial TC level was 22.5%. Overall false-positive rate was 19.0%, but false-positive rate for those initially assigned to the high category was 50%. Overall false-negative rate was 3.5%. Misclassification rates did not differ statistically on the basis of age, sex, blood pressure, smoking status, family history of coronary heart disease, presence of diabetes, obesity, the laboratory used, or whether the patient had fasted before giving blood.
Conclusions:
Single TC levels are too unreliable for diagnostic purposes, even if the subjects fast before testing. Family physicians should base their treatment decisions on the average of two cholesterol readings taken at different times 1 to 8 weeks apart.