From the Guidelines
For a 50-year-old female, a normal IGF-1 level is typically considered to be between 87-238 ng/mL, and a normal Z-score for IGF-1 should be between -2.0 and +2.0, as indicated by recent clinical guidelines 1.
Normal IGF-1 Levels and Z-Scores
The normal range for IGF-1 levels can vary slightly depending on the specific laboratory reference ranges. IGF-1 is an important hormone that mediates many of growth hormone's effects and plays a role in cell growth and metabolism.
- IGF-1 levels naturally decline with age, which is why age-specific reference ranges are used for interpretation.
- If your IGF-1 level falls outside the normal range, it's essential to discuss this with your healthcare provider as it could indicate conditions such as growth hormone deficiency (if low) or excess (if high).
Factors Affecting IGF-1 Levels
Other factors that can affect IGF-1 levels include:
- Nutritional status
- Liver function
- Kidney disease
- Certain medications These factors should be considered when interpreting IGF-1 results, as they can influence the accuracy of the diagnosis 1.
Clinical Interpretation
A diagnosis of GH excess is supported by an elevated serum IGF1 level in relation to the age-adjusted, sex-adjusted, and Tanner stage-matched normal range, as stated in recent guidelines 1.
- Elevated Tanner stage-matched and age-adjusted circulating serum IGF1 concentration is a reliable marker for GH excess.
- However, marginal or mild elevation in adolescence, during the peak growth spurt, needs cautious interpretation. It is crucial to interpret biochemical results within a clinical assessment of phenotype that includes height velocity, pubertal stage, and bone age, as suggested by recent studies 1.
From the Research
Normal IGF1 Levels and Z Score for a 50-Year-Old Female
- The normal level of IGF1 for a 50-year-old female is not explicitly stated in the provided studies, but it is mentioned that IGF1 levels decrease with age 2.
- The upper limit of normal (ULN) for IGF1 in middle-aged and elderly individuals is lower than historical reference ranges, making it more demanding to achieve IGF1 < 1× ULN 2.
- A study found that elevated IGF1 levels, alone, are sufficient to establish a diagnosis of acromegaly in the majority of clinically suspected cases, with a median standard deviation score (SDS) of +9.52 in patients with acromegaly 3.
- However, the SDS values for IGF1 in patients without acromegaly were -1.46 and -1.22, respectively, in two control groups 3.
- Another study found that 24% of postoperative patients with acromegaly had intermittent or persistent discordant values, with high IGF1 and normal GH levels 4.
- The study also found that the mean elevated IGF1 in the discordant population was 1.25 × ULN ± 0.17, with a range of 1.01-1.6 × ULN 4.
Z Score for IGF1
- The z score for IGF1 is not explicitly stated in the provided studies, but it is mentioned that IGF1 levels can be expressed as a standard deviation score (SDS) 3.
- The SDS is calculated by subtracting the mean IGF1 level for a given age and sex from the patient's IGF1 level, and then dividing by the standard deviation of the IGF1 levels for that age and sex 3.
- A study found that patients with acromegaly had a median SDS of +9.52, while patients without acromegaly had SDS values of -1.46 and -1.22, respectively, in two control groups 3.