Introduction
Fasting prior to blood collection has been a common practice in clinical laboratories to reduce preanalytical variability, which can influence the accuracy and interpretation of routine laboratory test results. However, it remains unclear whether differences in fasting duration before testing are clinically significant across a broad spectrum of common laboratory analytes. This retrospective study investigates the association between fasting duration and routine laboratory test outcomes, aiming to clarify which analytes are truly impacted by fasting time and whether these differences exceed established analytical performance standards.
Background
Preanalytical variables, including fasting state, can affect the concentrations of various substances measured in blood tests. Laboratories often recommend fasting for at least 8 hours before sample collection to reduce such variability, especially for glucose and lipid profiles. However, uniform fasting requirements may not be necessary for all tests, potentially prolonging patient discomfort and delaying diagnosis or treatment. Evaluating the clinical relevance of fasting duration on test results is essential for optimizing laboratory protocols and patient care.
Study Design and Methods
This single-center, retrospective cross-sectional study utilized data collected from February 2021 to December 2023 at a 670-bed secondary-care university hospital in Seoul, Republic of Korea. All blood samples were obtained from adult outpatient visits (individuals aged 18 years and older) at the hospital’s central phlebotomy unit. Each patient’s fasting duration was recorded based on the time elapsed between their last meal and the blood draw. Fasting times were categorized into three groups: less than 8 hours, 8 to 12 hours, and more than 12 hours.
To assess differences attributable to fasting duration, adjusted mean values across fasting groups were estimated using linear mixed-effects models with patient-level random intercepts, adjusting for age, sex, and clinical department. Additionally, paired within-person analyses were conducted for patients tested multiple times to reduce confounding from interpatient variability. Analytical performance specifications (APS) established by the European Federation of Clinical Chemistry and Laboratory Medicine were used as benchmarks to determine whether observed differences were clinically meaningful. Postprandial trends within the subgroup fasting less than 8 hours were also evaluated at 30-minute intervals.
Results
The study included 9,755,547 laboratory test results from 101,148 patients, covering 372 distinct test items. Initial between-group comparisons identified 27 analytes exhibiting differences exceeding the APS threshold. However, paired within-person analyses confirmed only 10 of these as truly significant, indicating that many differences were likely due to confounding factors.
The analytes significantly higher in patients with less than 8 hours fasting were glucose (10.8% increase), triglycerides (20.1%), γ-glutamyl transferase (GGT) (14.8%), and lipase (36.4%). No analyte showed APS-exceeding differences when comparing the 8 to 12 hours fasting group to the more than 12 hours group.
Within the less than 8 hours fasting subgroup, a progressive decrease in glucose and lactate concentrations was observed with longer fasting intervals, demonstrating statistically significant postprandial trends. In contrast, lipid concentrations did not show significant linear changes.
Discussion
This comprehensive analysis reveals that fasting duration notably affects only a few routine laboratory analytes beyond analytical variability thresholds—namely glucose, triglycerides, GGT, and lipase. These results affirm the clinical rationale behind fasting before glucose and lipid testing but challenge the necessity for uniform fasting periods for all tests.
The lack of significant differences between 8 to 12 hours and more than 12 hours fasting suggests extended fasting beyond 8 hours does not provide additional benefit for routine testing accuracy. The within-person paired analysis approach strengthened these findings by reducing confounders inherent in cross-sectional data, emphasizing the importance of individualized data interpretation.
Practically, these findings support revising laboratory fasting policies to be analyte-specific rather than universally applied, enhancing patient convenience without compromising test accuracy. For example, flexible fasting recommendations could be implemented for tests not affected by fasting duration, while maintaining stricter fasting for glucose and lipid measurements.
Limitations
The study’s retrospective design and reliance on documented fasting durations may introduce reporting inaccuracies. Additionally, the single-center setting in Korea may limit generalizability to other populations with different dietary habits or metabolic profiles. Future prospective, multicenter studies could validate and expand these findings.
Conclusions
Fasting duration before blood collection is associated with clinically relevant differences in only a limited number of routine laboratory analytes, chiefly glucose, triglycerides, γ-glutamyl transferase, and lipase. Differences between 8 to 12 hours and more than 12 hours fasting are not clinically significant. These data provide evidence to support developing analyte-specific fasting protocols rather than enforcing a uniform fasting requirement for all tests, potentially improving patient experience and laboratory efficiency.
Implications for Clinical Practice
Clinicians and laboratory professionals should consider these findings when advising patients about fasting before blood tests. Tailoring fasting instructions based on the specific tests ordered can help optimize test validity while reducing unnecessary fasting periods. This patient-centered approach aligns with current movements toward personalized medicine and improved patient compliance.
