Is an Insulin-like Growth Factor-1 (IGF-1) level of 80 considered low for a 60-year-old female with an Adrenocorticotropic Hormone (ACTH) level of 91, cortisol level of 20.5, a normal Dexamethasone (Dex) suppression test, and normal prolactin levels?

Evaluation of IGF-1 Level of 80 in a 60-Year-Old Female

An IGF-1 level of 80 in a 60-year-old female is likely below the age-adjusted reference range and warrants further evaluation for potential growth hormone deficiency, especially in the context of normal ACTH, cortisol, and prolactin levels.

Interpretation of the Laboratory Values

IGF-1 Assessment

• IGF-1 levels naturally decline with age, but a value of 80 in a 60-year-old female is likely at the lower end or below the age-adjusted normal range 1
• Low IGF-1 requires comparison to age-specific and sex-specific reference ranges for proper interpretation 2
• IGF-1 is a reliable marker for growth hormone status, with low levels suggesting potential growth hormone deficiency 3

Context of Other Laboratory Values

• Normal ACTH (91) and cortisol (20.5) with normal dexamethasone suppression test suggest intact hypothalamic-pituitary-adrenal axis function
• Normal prolactin levels rule out prolactinoma, which could otherwise affect pituitary function 2
• These findings together suggest a selective abnormality in the GH-IGF-1 axis rather than global pituitary dysfunction

Potential Causes of Low IGF-1

Growth Hormone Deficiency

• Primary consideration in patients with low IGF-1 levels, especially in the context of normal other pituitary hormones 4
• In adults over 40 years, IGF-1 values exceeding 15 nmol/l virtually exclude growth hormone deficiency, but values below this threshold warrant further investigation 3

Non-Functioning Pituitary Adenoma

• May cause local compression of normal pituitary tissue, leading to decreased GH production while other hormones remain normal 1, 5
• Can present with isolated GH deficiency before affecting other pituitary hormones

Confounding Factors

• Several conditions can cause falsely low IGF-1 values:
  • Severe hypothyroidism (should be ruled out)
  • Malnutrition or low energy availability 2
  • Severe infection
  • Oral estrogen therapy 2, 1
  • Liver disease 6

Recommended Evaluation

Initial Assessment

1. Confirm IGF-1 level with repeat measurement using the same assay
2. Complete pituitary hormone assessment:
   • TSH and free T4 to rule out hypothyroidism
   • FSH and LH to assess gonadal axis
   • Comprehensive metabolic panel to assess liver and kidney function

Specialized Testing

1. GH stimulation testing (insulin tolerance test or GHRH-arginine test) to confirm GH deficiency 1
2. Pituitary MRI to evaluate for potential microadenoma or other structural abnormalities

Clinical Implications

Health Consequences of Low IGF-1

• Decreased muscle mass and strength
• Increased adiposity
• Reduced bone mineral density (particularly concerning in a 60-year-old female) 2
• Impaired quality of life
• Altered lipid metabolism 1

Potential Pitfalls

• Misinterpreting IGF-1 levels without proper age-adjusted reference ranges
• Overlooking confounding factors that can lower IGF-1 independently of GH status
• Focusing only on one hormone axis without comprehensive pituitary evaluation
• Assuming normal ACTH/cortisol excludes all pituitary pathology 1

Management Considerations

If GH deficiency is confirmed:

• Consider GH replacement therapy based on clinical presentation and severity of deficiency
• Regular monitoring of IGF-1 levels to guide therapy
• Bone density assessment given increased osteoporosis risk
• Regular follow-up imaging if structural pituitary abnormality is identified

This patient's laboratory profile suggests a potential isolated GH deficiency that requires further specialized endocrinological evaluation to confirm the diagnosis and determine appropriate management.