When Laboratory Testing Turns Against Us:Human Anti-Mouse Antibody (HAMA) Interference with TSH and PTH Assays

Sadaf A. Farooqi, MD

Disclosure

No conflict of interest for the authors– Sadaf Farooqi, MD– Justin Moore, MD– Rami Mortada, MD– No financial incentives are involved in this

presentation

Introduction

• Heterophile antibodies, like Human Anti-Mouse Antibody (HAMA) can lead to falsely elevated levels of TSH and PTH• This occurs in specific “sandwich”

immunoassays, leading to expensive investigations and unnecessary treatments

Case Presentation

Case 1 24 yr. old with Hashimoto’s disease♀

Wide fluctuation in her TSH levels (76 to 276 mU/L) normal 0.5-5.0mU/L

Multiple escalations of her thyroid hormone dosage lead to a hospitalization for tachycardia

HAMA - 600ng/ml Levothyroxine replacement was reduced to a weight-based

dose (~1.6 mcg/kg/day) Free Thyroxine level was used for subsequent dose

adjustment

Case 2• 78 yr. old with CKD presented with secondary ♀

hyperparathyroidism and widely labile PTH levels over one year (60-899 pg/ml; normal 10-65 pg/ml)

• Serum Calcium and vitamin D levels unremarkable• Negative extensive evaluation, including a negative Sestamibi scan• HAMA titer 800ng/ml• Placed on activated vitamin D commensurate with her level of

renal function• Subsequently felt well and no further workup or management was

undertaken

Human Anti-Mouse Antibodies

Most commonly encountered Heterophile Antibody

10% of the population may have HAMA which can interfere with immunoassays results

Hetrophile Antibodies

HETROPHILE ANTIBODY

Monoclonal Antibodies

• HAMA have broad reactivity with antibodies of other animal species which are often source of assays antibody

• They can create both false positive and false negative results

Human Anti-Mouse Antibodies

“Sandwich” Assay True Positive

False Positive From Interfering

Heterophile Antibody

NO ANYLATE

CAPTURE ANTIBODY

HETEROHILEANTIBODY

LABEL ANTIBODY

Other Tests Affected By Heterophile Antibodies

• Tumor markers: CA 19-9, CEA, AFP• PSA• Troponin I• HCG• Hepatitis • Drug levels

Neutralizing The Effect Of HAMA Strategies

• Repeat test with different assay• HAMA/Heterophile blocking reagents• Serial dilutions• Nonspecific antibody-blocking tubes• Some commercial kits detect HAMA-positive

patient samples

What Should A Clinician Do?

• Consider Heterophile Antibody interference if there is a discrepancy between clinical presentation and laboratory values

• Clinicians should be aware of this type of interference in routine immunoassays

• Document exposure to drugs and screen patients

What Clinical Labs Should Do?

• Identify samples-dilution, blocking studies• HAMA assays• Encourage manufactures to make more

effective blockers• Communicate with physicians the limitations

of methodology

References

Baskin HJ, Cobin RH, Duick DS, et al. AACE thyroid guidelines. Endocr Pract 2002;8:457-69.

Sapin R, Agin A, Gasser F. Misleading high thyrotropin results obtained with a two-site immunometric assay involving a chimeric antibody. Clin Chem 2004;50:946-8. Baskin H J, Cobin R H, Duick D S. et al AACE thyroid guidelines. Endocr Pract 2002. 8457–469.469.

Hollowell J G, Staehling N W, Flanders W D. et al Serum TSH, T4 and thyroid antibodies in the United States population(1988–1994): National Health and Examination Survey (NHANES 3). J Clin Endocrinol Metab 2002. 87489–499.499.

Cooper D S. Clinical practice: subclinical hypothyroidism. N Engl J Med 2001. 345260–265.265.

Questions?