What are the typical laboratory tests for a 27-year-old patient with Down syndrome?

Laboratory Testing for Adults with Down Syndrome

For a 27-year-old new patient with Down syndrome, obtain a complete blood count, comprehensive metabolic panel, thyroid function tests (TSH and free T4), lipid panel, hemoglobin A1c, and celiac screening (tissue transglutaminase IgA with total IgA), as these address the most common and clinically significant comorbidities in this population.

Essential Laboratory Tests

Thyroid Function Testing

• TSH and free T4 should be measured simultaneously to distinguish primary hypothyroidism from central hypothyroidism, which can occur in Down syndrome 1
• Thyroid dysfunction is highly prevalent in adults with Down syndrome, with approximately 28% having abnormal thyroid function 2
• Hypothyroidism is the most common thyroid disorder in this population, with both congenital (1.8%) and compensated hypothyroidism (25.3%) being significantly elevated compared to the general population 2
• Annual thyroid screening is recommended for ongoing surveillance, though some evidence suggests this may be more frequent than necessary in the first two decades of life 3

Hematologic Assessment

• Complete blood count (CBC) is essential given the 20-fold increased risk of leukemia in individuals with Down syndrome 4
• Adults with Down syndrome demonstrate significant differences in hematological parameters compared to control populations 5
• The CBC also screens for anemia and other blood disorders that occur with increased frequency in this population 5

Metabolic and Biochemical Screening

• Comprehensive metabolic panel should be obtained as adults with Down syndrome show significant differences in biochemical parameters compared to controls 5
• Lipid panel and hemoglobin A1c are important given age- and sex-related differences in metabolic parameters in Down syndrome adults 5
• These tests help identify metabolic syndrome, diabetes, and cardiovascular risk factors that may be more prevalent in this population 5

Celiac Disease Screening

• Celiac disease occurs with increased frequency in Down syndrome
• Screen with tissue transglutaminase IgA antibody and total IgA level (to rule out IgA deficiency which would cause false-negative results)

Interpretation Considerations

Thyroid Function Test Interpretation

• TSH values above 6.5 mU/L are considered elevated in the general population 1
• For overt hypothyroidism (TSH >12 mU/L and/or free T4 <9 pmol/L), initiate levothyroxine therapy immediately after ruling out adrenal insufficiency 1
• Isolated TSH elevation (6-10 mU/L range) represents compensated hypothyroidism and may normalize spontaneously in up to 70% of cases 3
• Low TSH with low free T4 indicates central hypothyroidism, requiring evaluation for hypophysitis and morning ACTH/cortisol before starting thyroid replacement 1

Age-Related Considerations

• At 27 years old, this patient is in the age range where life expectancy may reach 60 years in developed countries, making comprehensive baseline laboratory assessment particularly important 5
• Age- and sex-related differences exist in several biochemical and hematological parameters in Down syndrome adults 5

Common Pitfalls to Avoid

• Do not measure TSH alone - always include free T4 to distinguish primary from central hypothyroidism 1
• Do not delay hematologic screening - the significantly elevated leukemia risk requires baseline CBC documentation 4
• Do not assume normal ranges apply - adults with Down syndrome have different baseline values for many parameters compared to the general population 5
• Do not overlook cardiac evaluation - while not a laboratory test, remember that 40% of individuals with Down syndrome have congenital heart disease, and cardiac assessment should accompany laboratory screening 4, 6

Follow-Up Testing Schedule

• Thyroid function tests should be repeated annually for ongoing surveillance 7, 2
• Patients with compensated hypothyroidism (TSH 6-10 mU/L) should be monitored every 3 months 2
• Monitor free T4 every 6-8 weeks during dose adjustments if levothyroxine therapy is initiated, targeting free T4 in the upper half of normal range 1
• Adherence to screening guidelines facilitates early diagnosis, as approximately 19% of patients with Down syndrome receive new thyroid disorder diagnoses when appropriately screened 7