Published: 27 Oct 2024

Establishing normal reference ranges for lab tests helps clinicians interpret whether a patient's results are within expected limits.
These ranges vary based on factors like age, gender, and specific methodologies used by different laboratories. Here's a guide to understanding and specifying lower and higher ranges for common lab tests for adults:

1. Blood Count Tests
White Blood Cell (WBC) Count: 4,500-11,000 cells/mcL
Red Blood Cell (RBC) Count:
Men: 4.7-6.1 million cells/mcL
Women: 4.2-5.4 million cells/mcL
Hemoglobin (Hb):
Men: 13.8-17.2 g/dL
Women: 12.1-15.1 g/dL
Hematocrit (Hct):
Men: 41-50%
Women: 36-44%
Platelet Count: 150,000-450,000/mcL

2. Electrolytes and Minerals
Sodium (Na): 135-145 mEq/L
Potassium (K): 3.5-5.0 mEq/L
Chloride (Cl): 96-106 mEq/L
Calcium (Ca): 8.5-10.5 mg/dL
Magnesium (Mg): 1.7-2.2 mg/dL
Phosphate: 2.5-4.5 mg/dL

3. Renal Function Tests
Blood Urea Nitrogen (BUN): 7-20 mg/dL
Creatinine:
Men: 0.6-1.2 mg/dL
Women: 0.5-1.1 mg/dL
Glomerular Filtration Rate (GFR): 90-120 mL/min (age-dependent, generally decreases with age)

4. Liver Function Tests
Alanine Aminotransferase (ALT): 7-56 U/L
Aspartate Aminotransferase (AST): 10-40 U/L
Alkaline Phosphatase (ALP): 44-147 U/L
Bilirubin: 0.1-1.2 mg/dL
Albumin: 3.5-5.0 g/dL

5. Thyroid Function Tests
Thyroid Stimulating Hormone (TSH): 0.4-4.0 mIU/L
Free T4 (Thyroxine): 0.8-1.8 ng/dL
Free T3 (Triiodothyronine): 2.3-4.1 pg/mL

6. Lipid Panel

Total Cholesterol: Below 200 mg/dL

LDL Cholesterol: Below 100 mg/dL (optimal)

HDL Cholesterol:

Men: Above 40 mg/dL

Women: Above 50 mg/dL

Triglycerides: Below 150 mg/dL

7. Glucose and Diabetes Markers

Fasting Blood Glucose: 70-99 mg/dL (fasting)

Hemoglobin A1c (HbA1c): Below 5.7% (for non-diabetics)

8. Inflammation Markers

C-Reactive Protein (CRP): Below 3.0 mg/L (high-sensitivity CRP can vary based on lab)

Erythrocyte Sedimentation Rate (ESR):

Men: 0-15 mm/hr

Women: 0-20 mm/hr

Tips for Specifying and Interpreting Ranges

Laboratory Reference Variability: Always consult the specific lab's reference ranges because slight variations may occur based on testing methods or local population norms.

Consider Patient Factors: Factors like age, gender, ethnicity, medications, and pre-existing conditions can influence normal ranges.

Adjusting Ranges for Comorbidities: Patients with chronic conditions may have adjusted ranges, especially for renal, liver, and glucose tests.

Clinical Context: A result outside the "normal" range may still be acceptable for some patients based on the clinical context and should be interpreted in conjunction with symptoms and history.

Lab ranges are essential benchmarks, but clinical correlation is crucial for accurate diagnosis and management.