Interpreting Abnormal Lab Values in a 99-Year-Old Female Patient
When interpreting laboratory values in a 99-year-old female patient, it is essential to recognize that many standard reference ranges are not appropriate for the elderly population, and what appears "abnormal" may actually represent normal physiological changes associated with advanced age.
Age-Related Changes in Laboratory Values
Common Age-Related Laboratory Alterations
- Serum alkaline phosphatase: May be elevated up to 2.5 times the normal range in healthy elderly individuals 1
- Fasting blood glucose: May be elevated up to 135-150 mg/dL without indicating pathology 1
- Postprandial glucose: May increase by approximately 10 mg/dL per decade of age 1
- Erythrocyte sedimentation rate (ESR): May be elevated up to 40 mm/hr in healthy elderly 1
- Hemoglobin: Lower acceptable levels are 11.0 g/dL in women and 11.5 g/dL in men 1
- BUN: May be elevated up to 28-35 mg/dL without indicating disease 1
- Creatinine: Normal serum creatinine may mask significantly decreased creatinine clearance 1, 2
Renal Function Assessment
- Creatinine clearance decreases by approximately 10 mL/min/1.73 m² per decade after age 40 3
- Normal serum creatinine values may exist despite markedly decreased renal function 1
- Consider using age-adjusted formulas when calculating GFR in very elderly patients
Interpreting Specific Laboratory Categories
Liver Function Tests
- Liver transaminases may be abnormal in certain metabolic disorders 3
- Minor elevations in liver enzymes should be interpreted cautiously, as they may not represent significant pathology in the elderly 2
Glucose Metabolism
- Glucose tolerance decreases with age
- Fasting glucose increases by 30-40 mg/dL per decade after age 40 3
- Higher glucose thresholds should be considered before diagnosing diabetes in the very elderly
Hematologic Parameters
- Anemia should not be dismissed as "normal aging" - lowest acceptable hemoglobin is 11.0 g/dL in women 1
- Platelet count decreases by approximately 20,000/mcL between the sixth and eighth decades 3
Approach to Abnormal Laboratory Values
Step 1: Consider Pre-analytical Variables
- Medication effects (particularly in polypharmacy situations common in elderly)
- Timing of sample collection (diurnal variations)
- Patient positioning and hydration status
- Fasting status
Step 2: Evaluate Clinical Context
- Compare with previous values when available
- Consider the patient's clinical presentation and symptoms
- Evaluate the magnitude of abnormality
Step 3: Consider Repeat Testing
- For unexpected results without clinical correlation, consider repeating the test
- Be aware of intraindividual biological variation 2
Step 4: Interpret in Context of Age-Specific Changes
- Use age-appropriate reference ranges when available
- Consider physiological changes of aging before pursuing extensive workup
Pitfalls to Avoid
Overreaction to minor abnormalities: Do not initiate extensive workups for minor deviations that may represent normal aging 2
Underdiagnosis: Do not dismiss all abnormal values as "just aging" - some may represent true pathology requiring intervention 4
Overtreatment: Treating laboratory "abnormalities" that represent normal aging may be harmful 5
Failure to consider medication effects: Many elderly patients take multiple medications that can affect laboratory values
Using standard reference ranges: Traditional reference ranges are often established using younger populations and may not apply to the very elderly 6
By understanding the physiological changes that occur with advanced age and their impact on laboratory values, clinicians can avoid unnecessary testing, inappropriate diagnoses, and potentially harmful treatments in elderly patients.