Differential Diagnosis - Symptoms that don't have one clear cause

Laboratory test ranges are critical for interpreting results, as they help to determine if a value is within a normal range or indicates a potential health concern. Here are steps to specify and interpret lower and higher ranges of common lab tests for adults:

1. Understand Reference Ranges

- Reference ranges typically represent the range of values seen in 95% of healthy adults, meaning that 5% of healthy individuals may fall outside of these ranges. These are generally provided by the testing laboratory and may vary slightly between labs due to differences in equipment, techniques, and population samples.

2. Consult Established Guidelines

- Professional health organizations like the American Heart Association (AHA), American Diabetes Association (ADA), and National Institute of Health (NIH) provide recommended ranges for lab tests.

- Use the laboratory's provided reference ranges on the report, as they account for specific methodologies and demographics.

3. Typical Ranges for Common Lab Tests (General Adult Reference)

- Complete Blood Count (CBC)

- White Blood Cells (WBC): 4,500–11,000 cells/mcL

- Red Blood Cells (RBC): 4.5–5.9 million cells/mcL (men), 4.1–5.1 million cells/mcL (women)

- Hemoglobin (Hgb): 13.8–17.2 g/dL (men), 12.1–15.1 g/dL (women)

- Hematocrit (Hct): 40.7–50.3% (men), 36.1–44.3% (women)

- Platelets: 150,000–450,000 cells/mcL

- Basic Metabolic Panel (BMP)

- Sodium: 135–145 mEq/L

- Potassium: 3.5–5.0 mEq/L

- Calcium: 8.5–10.2 mg/dL

- Blood Urea Nitrogen (BUN): 7–20 mg/dL

- Creatinine: 0.6–1.2 mg/dL (may vary slightly by gender and age)

- Liver Function Tests (LFTs)

- Alanine Aminotransferase (ALT): 7–56 U/L

- Aspartate Aminotransferase (AST): 10–40 U/L

- Alkaline Phosphatase (ALP): 44–147 U/L

- Bilirubin (Total): 0.1–1.2 mg/dL

- Lipid Panel

- Total Cholesterol: Less than 200 mg/dL

- LDL (Low-Density Lipoprotein): Less than 100 mg/dL (optimal); 100-129 mg/dL (near optimal)

- HDL (High-Density Lipoprotein): 40 mg/dL or higher (men); 50 mg/dL or higher (women)

- Triglycerides: Less than 150 mg/dL

- Thyroid Function Tests

- Thyroid-Stimulating Hormone (TSH): 0.4–4.0 mIU/L

- Free T4 (Thyroxine): 0.8–1.8 ng/dL

- Blood Glucose Levels

- Fasting Glucose: 70–99 mg/dL (normal), 100–125 mg/dL (prediabetes), 126 mg/dL or higher (diabetes)

- Hemoglobin A1c: Below 5.7% (normal), 5.7–6.4% (prediabetes), 6.5% or higher (diabetes)

4. Consider Age, Gender, and Health Conditions

- Age: For example, older adults may have slightly different ranges for WBC and kidney function markers.

- Gender: Certain ranges, like those for hemoglobin, vary between men and women due to physiological differences.

- Chronic Conditions: Adjustments may be necessary for people with chronic conditions, such as heart or kidney disease.

5. Interpreting Low and High Values

- Low Value: A lab result below the lower limit may indicate a deficiency, poor organ function, or disease.

- High Value: A result above the higher limit may suggest inflammation, infection, or an overactive organ/system.

- Always interpret within context, as one-time abnormal results may not always indicate a serious issue.

6. Use Laboratory-Specific References and Clinical Context

- Confirm with Laboratory: Since testing methods and populations can vary, always refer to the range provided by the testing lab.

- Clinical Symptoms: Reference ranges should always be interpreted alongside the patient’s symptoms and clinical history for accurate assessment.

Reference ranges are helpful but need individualized interpretation by healthcare professionals, as numerous factors influence lab results.