How do you check growth hormone levels in a 17-year-old?

How to Check Growth Hormone Levels in a 17-Year-Old

Growth hormone (GH) levels in a 17-year-old should be assessed primarily through serum IGF-1 measurement matched to Tanner stage, sex, and age, combined with clinical growth parameters, rather than direct GH testing, as standard GH suppression tests are unreliable in adolescents. 1

Initial Clinical Assessment

Start by evaluating growth parameters and pubertal development:

• Plot current height, height velocity over the past 6-12 months, and calculate mid-parental target height to determine if growth concerns are present 1
• Document Tanner stage to assess pubertal development, as this is essential for contextualizing GH dynamics and interpreting biochemical results 2
• Obtain left wrist radiograph to assess bone age and determine remaining growth potential (whether epiphyses remain open) 2, 1

Biochemical Testing

The primary biochemical assessment involves:

• Measure serum IGF-1 level and compare to local Tanner stage-matched, sex-matched, and age-matched reference ranges 2, 1
• Measure thyroid function (TSH and free T3 or free T4) to exclude hypothyroidism, which can falsely lower IGF-1 and independently cause growth failure 2, 1

Critical Interpretation Caveats for IGF-1

IGF-1 results require careful interpretation in adolescents:

• Marginal or mild IGF-1 elevation during mid-puberty (Tanner stage 2-3) needs cautious interpretation, as this is the peak growth spurt period 2
• IGF-1 may be falsely low with concurrent severe hypothyroidism, malnutrition, or severe infection 2, 1, 3
• IGF-1 may be falsely elevated with poorly controlled diabetes mellitus, hepatic/renal failure, or in girls taking oral estrogens 2, 1, 3
• Inter-assay variability is significant, so use local laboratory reference ranges 2, 1

Why Direct GH Testing Is Problematic in Adolescents

Standard GH suppression testing (oral glucose tolerance test) is unreliable in this age group:

• Approximately 30% of normally growing tall adolescents fail to suppress GH below 1 μg/L after glucose load despite being completely normal 2, 1, 3
• GH suppression is sex and pubertal stage-specific in adolescents, with highest levels in mid-puberty (Tanner stage 2-3), particularly in girls 2, 3
• The adult cutoff of <1 μg/L cannot be reliably applied to adolescents undergoing normal pubertal development 2, 1

When GH Suppression Testing May Be Considered

If GH excess (not deficiency) is suspected based on clinical features:

• Administer oral glucose load (1.75 g/kg, maximum 75g or 2.35 g/kg, maximum 100g) 3
• Measure GH at baseline and multiple time points after glucose administration 3
• Failure to suppress GH must be interpreted alongside clinical features and IGF-1 levels, not in isolation 2, 3

Practical Algorithm for a 17-Year-Old

Follow this sequence:

1. Measure height, calculate height velocity, assess Tanner stage, and calculate mid-parental target height 1
2. Order serum IGF-1 (with Tanner stage-matched reference ranges) and thyroid function tests (TSH, free T4) 2, 1
3. Obtain left wrist radiograph for bone age 2, 1
4. Interpret IGF-1 in context of Tanner stage, clinical growth pattern, and potential confounders 2, 1
5. If IGF-1 is low and growth velocity is decreased, consider GH deficiency and refer to pediatric endocrinology for provocative GH stimulation testing 1
6. If IGF-1 is elevated with accelerated growth, consider GH excess and potentially perform glucose suppression testing 2, 3

Additional Metabolic Screening

Before considering any GH-related intervention, assess:

• Serum creatinine, electrolytes, bicarbonate, calcium, phosphorus, alkaline phosphatase, albumin, fasting glucose, and hemoglobin A1c to exclude other causes of growth disturbance 2
• Parathyroid hormone and 25-OH vitamin D if chronic kidney disease or metabolic bone disease is suspected 2

Common Pitfalls to Avoid

Do not rely on random GH levels, as GH is secreted in a pulsatile fashion and random measurements are meaningless 1

Do not use IGFBP-3 in patients with chronic kidney disease, as low-molecular-mass fragments accumulate and cause falsely elevated results 2

Do not interpret biochemical results without considering clinical context, including growth velocity, pubertal stage, and bone age 2, 1