When Laboratory Testing Turns Against Us - PowerPoint Presentation

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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

A

ntibody (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)

F

ree

T

hyroxine

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 Antibody10% 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 antibodyThey can create both false positive and false negative results

Human Anti-Mouse Antibodies

“Sandwich” Assay True

P

ositive

False Positive

F

rom

I

nterfering 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

H

eterophile

A

ntibody 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?