The interpretation of any clinical laboratory test is done by comparing the patient’s results to the test’s reference intervals. For example, the reference interval for white blood cells (WBC) in human adults is 4,500 - 11,000 cells/microliter. Estimation of this reference interval is done by testing:​

Correct option is A

Reference intervals for clinical laboratory tests are established using statistical analysis of a large population of healthy individuals. The reference range typically represents the central 95% of values, meaning that 2.5% of the lowest and 2.5% of the highest values are excluded.

• The reference interval is calculated by measuring the biomarker (e.g., WBC count) in a large number of healthy individuals, ensuring it reflects normal physiological levels.
• The 95% reference interval corresponds to the range between the 2.5th percentile and the 97.5th percentile.
• This range helps clinicians determine if a patient’s test result falls within the expected normal variation or indicates a potential abnormality requiring further investigation.

Let’s evaluate the given options:

• Option 1 (Correct): A large number of healthy adults are used, and the range is estimated between the 2.5th and 97.5th percentiles, which correctly represents a 95% reference interval.
• Option 2 (Incorrect): The 5th to 95th percentile range represents a 90% reference interval, not the commonly used 95% reference interval.
• Option 3 (Incorrect): Uses a random selection of adults, which may include unhealthy individuals, potentially skewing the reference values.
• Option 4 (Incorrect): The -1.64 to +1.64 standard deviation range represents a 90% confidence interval, which is different from the 95% reference interval used in clinical testing.

Thus, Option 1 is the correct answer.

Information Booster:

1. Definition of Reference Interval: A range of values within which 95% of healthy individuals fall, typically between 2.5th and 97.5th percentiles.
2. Clinical Importance: Reference intervals help clinicians distinguish between normal and abnormal test results.
3. Exclusion of Outliers: The top 2.5% and bottom 2.5% of values are removed to account for natural biological variations.
4. Population Considerations: Reference intervals are established based on age, sex, ethnicity, and other demographic factors.
5. Common Use in Lab Medicine: Blood tests like WBC count, hemoglobin levels, and cholesterol levels use 95% reference intervals.
6. Statistical Basis: A Gaussian (normal) distribution assumption is used, but some tests may require non-parametric methods.
7. Difference from Confidence Interval: A confidence interval estimates where the true mean of a population lies, whereas a reference interval describes the normal range for healthy individuals.