Real Pregnancy or Uncontrolled Hypothyroidism?

Christie G. Turin1,MD; Anisha Gupta1, MD; Susan Samson1,2, MD; Mandeep Bajaj1,2, MBBS

Baylor College of Medicine, Houston, TX 1; CHI-St. Luke’s Episcopal Health System, Houston, TX2

Outline

1. Objectives 2. Case presentation3. History of TSH 4. TSH structure5. TSH assay6. β-hCG & TSH assay cross reactivity7. Pregnancy and hypothyroidism8. Conclusions

Objectives

Objectives

• To illustrate a case of a young woman of reproductive age with typical

hypothyroid symptoms and a false home and in-hospital pregnancy

test

• To present the history of the development of the TSH assay and how it

has changed over time

• To differentiate TSH from other structurally-similar hormones

• To demonstrate a case of false positive pregnancy tests due to cross-

reactivity of hCG with TSH on modern IMCA assays

• To recognize the presence of other non-hCG substances that could

affect the hCG level

Case Presentation

Case Presentation

History of Present Illness

• 27-year-old woman originally from Turkey with history of hypothyroidism presented with progressive fatigue, cold intolerance, constipation, and weight gain, shortness of breath.

• Reported a positive home pregnancy test with a delayed menstrual cycle (LMP 7 weeks ago)

Past Medical History• Hypothyroidism since 2009

Past Surgical History• Denies previous surgical history

Social History• Denies tobacco, alcohol, or illicit

drugs use

Physical Exam

T: 98.5°F HR: 56 bpm BP: 113/71mmHg RR:18 SpO2: 100%

General appearance: resting, in no acute distress

Neck: no thyromegaly, no JVD, no LAD

Cardiovascular: bradycardic, regular rhythm, no murmurs

Respiratory: CTAB, no rales

Gastrointestinal: soft, non-tender, non-distended, BS +

Pelvic: no vaginal bleeding

Extremities: no lower extremities edema

Neurological: AAOx4, no focal deficits

Laboratory

Endovaginal Ultrasound

•No intrauterine gestational sac

Labs and Imaging

• TSH 80.59 uIU/mL

• Free T4: 0.67 ng/dL

• hCG 262 mIU/mL

Follow up

• Patient was started on IV levothyroxine

•Repeat hCG 194mIU/mL, continued to downtrend

•No signs of vaginal bleeding

•Discharged to home on oral levothyroxine 300 mcg daily (5mcg/kg/day). Down-titrated to 200 mcg (2.8 mcg/kg/day)

• TSH improved to 0.6uIU/mL, hCG undetectable

• Patient resumed a normal menstrual cycle with normalization of thyroid function

History of TSH

History of TSH

• 1926: Eduard Uhlenhuth from the University of Maryland, first to demonstrate that the anterior lobe of the pituitary gland secreted a thyroid stimulator1

• 1970s: Determination of primary structure of TSH2

• 1994: Elucidation of the crystal structure of the closely related human chorionic gonadotropin (hCG) 3

1.Uhlenhuth E. Br J Exp Biol . 1927; 5:1–5. 2. Magner JA . Endocr Rev. 1990; 11:354–385. 3. Lapthorn AJ. Nature. 1994; 369:455–461.

TSH Structure

TSH Structure

• 28-kD to 30-kD glycoprotein synthesized by thyrotrophic basophils in the adenohypophysis

• Composed of two non-covalently linked subunits: α and β

• α chain is shared by hCG, LH, FSH

• Biological specificity of each glycoprotein hormone is conferred by the β chain

Szkudlinski. Physiol Rev. 2002 Apr;82(2):473-502.

TSH and hCG

•Both glycoproteins have a common α-subunit and there is a 38% sequence identity between the hCG β-subunit and TSH β-subunit.1

Szkudlinski. Physiol Rev. 2002 Apr;82(2):473-502.

TSH Assay

TSH Assay

• 1965: radioimmunoassay (RIA) of hTSH. Detection limit of ~1mIU/L1,2

• 1984: immunoradiometric assay (IMA) with better sensitivity and short incubation times3. Uses a combination of monoclonal antibodies targeting different TSH epitope(s) in a “sandwich” format. Detection limit as low as 0.3-0.4mIU/L

• 1990s: Third-generation of TSH IMAs, achieving sensitivity of 0.01mIU/L

1. Utiger RD . J Clinc Invest. 1965; 44: 1277-1286 2. Ridgeway EC. Mayo Clin Proc. 1988; 63: 1028-1034 3. Seth J. Br Med J (Clin Res Ed). 1984;

289(6455): 1334–1336

Immunoradiometric assay

(IMA): TSH in patient’s

serum is added to tube with

monoclonal TSH-

antibodies. Labeled anti-

TSH antibodies are added,

which are detected after

binding occurs.

TSH Assay

Picture obtained from: Stanley. Essentials of Immunology & Serology

TSH Assay

• Different non-isotopic signals • Immunoenzymometric assays (IEMA) used enzyme

• Immunofluorometric assays (IFMA) used fluorophors

• Immunochemiluminometric assays (ICMA) used chemiluminescent molecules

• Immunobioluminometric assays (IBMA) used bioluminescent signal molecules

• Current TSH assays are automated ICMAs, achieving a functional sensitivity ≤0.01 mIU/L. Currently considered standard of care

Hay ID. Clin Chem 1991; 37:2002 - 2008

TSH – hCG Cross Reactivity

hCG assay

1966: Midgley described the first radioimmunoassay forhCG – however, it didn’t differentiate between hCG andLH

1972: Vaitukaitis, Braunstein, and Ross developed aspecific radioimmunoassay which specifically measuredβ-subunit of hCG

Vaitukaitis JL. Am J Obstet Gynecol. 1972 Jul 15;113(6):751-8.

TSH and hCG Cross Reactivity

β-hCG assay has a mean analytical specificity of <10% cross reactivity with TSH

** Cross reactivity was calculated as % interference (β-hCG supplemented with 100 mIU/L TSH)**

More information available in: http://www.ilexmedical.com/files/PDF/TotalBhCG_ARC.pdf

Other causes of false hCG elevation

Interference by other non-hCG substances:1, 2

• Heterophilic antibodies

• Nonspecific protein binding

• hCG-like substances

• Trophoblastic or non-trophoblastic neoplasms

Boscato LM. Clin Chem 1988;34:27-33.

Hussa RO. Obstet Gynecol 1985;65:211-9.

Pregnancy and Hypothyroidism

Pregnancy and Hypothyroidism

•Women with hypothyroidism have decreased fertility: difficulties conceiving, increased risk of abortion.

• Increased risk of maternal complications: gestational hypertension, anemia, abuptio placenta and postpartum hemorrhage.

• Increased risk of neonatal complications: preterm birth, low birth weight, respiratory distress

Abalovich M. Thyroid. 2002;12:63-66

Pregnancy and Subclinical hypothyroidism

• Two parallel, randomized, placebo-controlled trials including women with subclinical hypothyroidism or hypothyroxinemia

• Subclinical hypothyroidism: 97 vs 94 IQ score (p: 071)

• Hypothyroxinemia: 94 vs 91 IQ score (p: 0.30)

• No significant effect on neurodevelopmental outcomes in children whose mothers had received thyroxine treatment.

N Engl J Med. 2017 Mar 2;376(9):815-825

Conclusions

Conclusions

1. A low quantitative β-hCG without evidence of pregnancy could be explained by the cross reactivity that this test has with the TSH assay (which may occur when TSH level is above 100 mIU/L).

2. A downtrending β-hCG level was noted as the hypothyroidism was treated, consistent with a false-positive pregnancy test.

3. Levothyroxine therapy in early stages of pregnancy in patients with hypothyroidism is imperative to multiple maternal and neonatal complications.

References

References 1. Uhlenhuth E, et al. The anterior lobe of the hypophysis as a control mechanism of the function of the thyroid gland. Br J Exp Biol . 1927; 5:1–5

2. Magner JA , et al. Thyroid-stimulating hormone: biosynthesis, cell biology, and bioactivity. Endocr Rev. 1990; 11:354–385.

3. Lapthorn AJ, et al. Crystal structure of human chorionic gonadotropin. Nature. 1994; 369:455–461.

4. Szkudlinski, et al. Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships. Physiol Rev. 2002 Apr;82(2):473-502.

5. Utiger RD, et al. Radioimmunoassay of human plasma rhyrotropin. J Clinc Invest. 1965; 44: 1277-1286

6. Ridgeway EC , et al. Thyrotropin radioimmunoassays: Birth, life, and demise. Mayo Clin Proc. 1988; 63: 1028-1034

7. Seth J. A sensitive immunoradiometric assay for serum thyroid stimulating hormone: a replacement for the thyrotrophin releasing hormone test? Br Med J (Clin Res Ed). 1984 Nov 17; 289(6455): 1334–1336

8. Casey BM, et al. Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy. N Engl J Med. 2017 Mar 2;376(9):815-825.

9. Hay ID, et al. American Thyroid Association Assessment of Current Free Thyroid Hormone and Thyrotropin Measurements and Guidelines for Future Clinical Assays. Clin Chem 1991; 37:2002 – 2008

10. Vaitukaitis JL, et al. A radioimmunoassay which specifically measures human chorionic gonadotropin in the presence of human luteinizing hormone. Am J Obstet Gynecol. 1972 Jul 15;113(6):751-8.

11. Total β-hCG.Available at: http://www.ilexmedical.com/files/PDF/TotalBhCG_ARC.pdf

12. Boscato LM, et al. Heterophilic Antibodies: A Problem for All Immunoassays. Clin Chem 1988;34:27-33.

13. Hussa RO, Rinke ML, Schweitzer PG. Discordant Human Chorionic Gonadotropin Results: Causes and Solutions. ObstetGynecol 1985;65:211-9.

14. Abalovich M, et al. Overt and subclinical hypothyroidism complicating pregnancy. Thyroid. 2002;12:63-66

Thank you