STUDY SUMMARY
There’s no difference between fasting and nonfasting LDL
Doran et al1 used data from the NHANES III survey to compare the prognostic value of fasting versus nonfasting LDL for all-cause mortality and cardiovascular mortality. NHANES III is a nationally representative cross-sectional survey that was conducted from 1988 to 1994.13 Doran et al1 included 16,161 US adults ages 18 and older for whom data on fasting time were available. Participants for whom LDL calculations were not possible (due to missing HDL, TC, or triglyceride levels) were excluded. Those with triglycerides ≥ 400 mg/dL were excluded from the primary analysis.
Participants were stratified based on fasting status (≥ 8 hours or < 8 hours) and followed for a mean of 14 years. To control for possible confounders, the researchers used propensity score matching to identify 4,299 pairs of fasting and nonfasting individuals with similar cardiovascular risk factors, including race, smoking history, prior cardiovascular disease, cholesterol medication use, diabetes, elevated TC, low HDL, hypertension, enlarged waist circumference, and low socioeconomic status. After matching, the baseline characteristics of the fasting and nonfasting groups were similar.
The primary outcome was all-cause mortality, and the secondary outcome was cardiovascular mortality. The prognostic value of fasting and nonfasting LDL for these outcomes was evaluated as the area under the receiver operator characteristic (ROC) curve using the Hosmer-Lemeshow C-statistic.14 (In this case, similar C-statistics indicate that the tests have similar prognostic values.*) Kaplan-Meier curves were used to assess survival. The association of LDL with mortality, after adjustment for potential confounders, was evaluated using Cox proportional hazard models. The groups were divided into tertiles based on LDL levels (< 100 mg/dL, 100-130 mg/dL, and > 130 mg/dL).
As expected, compared to individuals in the first LDL tertile (< 100 mg/dL), those with a higher LDL had an increased risk for all-cause mortality (hazard ratios [HR], 1.61 for the second tertile and 2.10 for the third tertile). The prognostic value of fasting versus nonfasting status for predicting all-cause mortality was similar, as suggested by the C-statistics (0.59 vs 0.58; P = .73).
The risk for cardiovascular mortality also increased with increasing LDL tertiles. As was the case with all-cause mortality, the prognostic value of fasting versus nonfasting status was similar for predicting cardiovascular mortality as observed by similar C-statistics (0.64 vs 0.63; P = .49). In addition, fasting versus nonfasting C-statistics were similar for both diabetic and nondiabetic patients.
WHAT’S NEW
Results suggest fasting may no longer be necessary
While obtaining a fasting lipid panel is recommended by multiple guidelines and has become traditional practice, the need for fasting originated primarily out of concern for the effect of postprandial triglycerides on calculating LDL. This is the first study that compared the prognostic value of fasting and nonfasting LDL levels for predicting mortality; it demonstrated that they are essentially the same.
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