From the Guidelines
Normal lab values are standardized ranges that indicate healthy functioning of various body systems, and according to the most recent study 1, common normal values include liver function tests with ALT levels of 29 to 33 IU/L for men and 19 to 25 IU/L for women. These reference ranges vary slightly between laboratories due to differences in testing methods and equipment calibration. Common normal values also include:
- Complete blood count parameters (hemoglobin 12-16 g/dL for women, 13.5-17.5 g/dL for men; white blood cells 4,500-11,000/μL)
- Basic metabolic panel values (sodium 135-145 mEq/L, potassium 3.5-5.0 mEq/L, glucose 70-99 mg/dL fasting)
- Kidney function markers (creatinine 0.6-1.2 mg/dL for men, 0.5-1.1 mg/dL for women)
- Lipid panel (total cholesterol <200 mg/dL, LDL <100 mg/dL, HDL >40 mg/dL for men, >50 mg/dL for women)
- Thyroid function tests (TSH 0.4-4.0 mIU/L) It's essential to note that laboratory test values may differ substantially between testing facilities and among populations, as highlighted in the study 1, which found significant racial/ethnic differences in distribution for many laboratory tests. Additionally, the study 1 emphasizes the importance of laboratories establishing their own reference ranges to ensure accuracy and reliability. Values slightly outside these ranges don't necessarily indicate illness, as individual variation exists, but significant deviations warrant further investigation.
From the Research
Normal Lab Values
Normal lab values, also known as reference ranges, are the standard values used to interpret laboratory test results. These values are typically established by testing a large number of healthy individuals and determining the average range of values for a particular test.
Establishment of Normal Values
The process of establishing normal values involves testing at least 120 healthy individuals in a given age-group, gender, ethnicity, and testing method 2. The central 95% of the values is usually adopted as the normal range, which means that 5% of healthy individuals will have abnormal laboratory results by definition.
Factors Affecting Laboratory Test Results
Several factors can affect laboratory test results, including:
- Variations in testing methods at different laboratories
- Age, gender, and ethnicity
- Seasonality
- Random variations
- Cultural, biological, physiological, and behavioral diversity in the population sampled to determine normality 3
Examples of Normal Lab Values
Some examples of normal lab values include:
- Complete Blood Count (CBC) components, such as white blood cell count, hemoglobin, and platelet count 4
- Liver function tests, such as alanine transaminase (ALT) and aspartate transaminase (AST) 5, 6
- Chest X-ray results, which are typically used to screen for occult metastatic disease in cancer patients 5, 6
Clinical Significance of Laboratory Test Results
The clinical significance of laboratory test results can be affected by various factors, including the patient's medical history, symptoms, and physical examination findings. It is essential to consider these factors when interpreting laboratory test results and to communicate the results to patients in a clear and concise manner 2.