Transcript Human Anti-Mouse Antibody

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 AntiMouse 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
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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 weightbased 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
Human Anti-Mouse 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
“Sandwich” Assay True Positive
False Positive From Interfering
Heterophile Antibody
NO ANYLATE
CAPTURE
ANTIBODY
HETEROHILE
ANTIBODY
LABEL
ANTIBODY
Other Tests Affected By
Heterophile Antibodies
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Tumor markers: CA 19-9, CEA, AFP
PSA
Troponin I
HCG
Hepatitis
Drug levels
Neutralizing The Effect Of HAMA
Strategies
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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?