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Reference limits of serum TSH and free T4 are significantly influenced by race and age in an urban outpatient medical practice.

Abstract

OBJECTIVE

The suitability of TSH reference limits derived from national databases to outpatient practices has not been established. We aimed to determine whether race and age influence the distribution of TSH and free T4 (fT4).

DESIGN

A cross-sectional study of an urban outpatient medical practice.

PARTICIPANTS

Patients (n = 22,116) without clinical evidence of thyroid disease or use of thyroid-specific medications.

MEASUREMENTS

Comparison of TSH and fT4 distributions in specific racial and age groups including blacks, whites and Hispanics.

RESULTS

TSH was distributed at higher concentrations, without skew, in whites compared to blacks (median, 1.54 mIU/l vs. 1.18 mIU/l, P < 0.001) and in old (>80 years old) compared to young (20-29 years old) (median, 1.61 mIU/l vs. 1.13 mIU/l, P < 0.001). In all patients, blacks and whites, 3%, 8% and 5%, respectively, of those aged > 80 years were misclassified as having high TSH compared to those aged 20-29 years (P < 0.001). Using TSH limits from national databases resulted in significant misclassification of patients with raised or lowered TSH. Mean fT4 was significantly lower in blacks than whites (17.5 +/- 4.38 pmol/l vs. 18.3 +/- 3.99 pmol/l, P < 0.001), did not differ between young and old, but decreased progressively (average 7%) as TSH increased to > 4.5 mIU/l.

CONCLUSIONS

Reference limits for TSH differ between races and with age. Use of race- and age-specific reference limits decreases misclassification of patients with lowered or raised TSH in an urban practice. The unique fT4:TSH relationships of blacks and whites may be genetically determined. The implications of the small decrement in fT4 as TSH increases remain to be explored.

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  • Publisher Full Text
  • Authors+Show Affiliations

    ,

    Department of Medicine, Montefiore Medical Center and Albert Einstein College of Medicine, Bronx, NY 10467, USA. lboucai@montefiore.org

    Source

    Clinical endocrinology 70:5 2009 May pg 788-93

    MeSH

    Adolescent
    Adult
    African Americans
    Age Factors
    Aged
    Aged, 80 and over
    Child
    Child, Preschool
    Cross-Sectional Studies
    European Continental Ancestry Group
    Female
    Hispanic Americans
    Humans
    Hypothyroidism
    Infant
    Infant, Newborn
    Male
    Middle Aged
    New York City
    Nutrition Surveys
    Reference Values
    Thyrotropin
    Thyroxine
    Young Adult

    Pub Type(s)

    Comparative Study
    Journal Article

    Language

    eng

    PubMed ID

    18727705

    Citation

    Boucai, Laura, and Martin I. Surks. "Reference Limits of Serum TSH and Free T4 Are Significantly Influenced By Race and Age in an Urban Outpatient Medical Practice." Clinical Endocrinology, vol. 70, no. 5, 2009, pp. 788-93.
    Boucai L, Surks MI. Reference limits of serum TSH and free T4 are significantly influenced by race and age in an urban outpatient medical practice. Clin Endocrinol (Oxf). 2009;70(5):788-93.
    Boucai, L., & Surks, M. I. (2009). Reference limits of serum TSH and free T4 are significantly influenced by race and age in an urban outpatient medical practice. Clinical Endocrinology, 70(5), pp. 788-93. doi:10.1111/j.1365-2265.2008.03390.x.
    Boucai L, Surks MI. Reference Limits of Serum TSH and Free T4 Are Significantly Influenced By Race and Age in an Urban Outpatient Medical Practice. Clin Endocrinol (Oxf). 2009;70(5):788-93. PubMed PMID: 18727705.
    * Article titles in AMA citation format should be in sentence-case
    TY - JOUR T1 - Reference limits of serum TSH and free T4 are significantly influenced by race and age in an urban outpatient medical practice. AU - Boucai,Laura, AU - Surks,Martin I, Y1 - 2008/08/25/ PY - 2008/8/30/pubmed PY - 2009/7/31/medline PY - 2008/8/30/entrez SP - 788 EP - 93 JF - Clinical endocrinology JO - Clin. Endocrinol. (Oxf) VL - 70 IS - 5 N2 - OBJECTIVE: The suitability of TSH reference limits derived from national databases to outpatient practices has not been established. We aimed to determine whether race and age influence the distribution of TSH and free T4 (fT4). DESIGN: A cross-sectional study of an urban outpatient medical practice. PARTICIPANTS: Patients (n = 22,116) without clinical evidence of thyroid disease or use of thyroid-specific medications. MEASUREMENTS: Comparison of TSH and fT4 distributions in specific racial and age groups including blacks, whites and Hispanics. RESULTS: TSH was distributed at higher concentrations, without skew, in whites compared to blacks (median, 1.54 mIU/l vs. 1.18 mIU/l, P < 0.001) and in old (>80 years old) compared to young (20-29 years old) (median, 1.61 mIU/l vs. 1.13 mIU/l, P < 0.001). In all patients, blacks and whites, 3%, 8% and 5%, respectively, of those aged > 80 years were misclassified as having high TSH compared to those aged 20-29 years (P < 0.001). Using TSH limits from national databases resulted in significant misclassification of patients with raised or lowered TSH. Mean fT4 was significantly lower in blacks than whites (17.5 +/- 4.38 pmol/l vs. 18.3 +/- 3.99 pmol/l, P < 0.001), did not differ between young and old, but decreased progressively (average 7%) as TSH increased to > 4.5 mIU/l. CONCLUSIONS: Reference limits for TSH differ between races and with age. Use of race- and age-specific reference limits decreases misclassification of patients with lowered or raised TSH in an urban practice. The unique fT4:TSH relationships of blacks and whites may be genetically determined. The implications of the small decrement in fT4 as TSH increases remain to be explored. SN - 1365-2265 UR - https://www.unboundmedicine.com/medline/citation/18727705/Reference_limits_of_serum_TSH_and_free_T4_are_significantly_influenced_by_race_and_age_in_an_urban_outpatient_medical_practice_ L2 - https://doi.org/10.1111/j.1365-2265.2008.03390.x DB - PRIME DP - Unbound Medicine ER -