Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (989 page)

   Interpretation

Increased In

   Normal pregnancy

   Recent termination of pregnancy

   Gestational trophoblastic disease

   Choriocarcinoma and some germ cell tumors

   Hydatiform mole

Decreased In

   Threatened abortion; microabortion

   Ectopic pregnancy

   Limitations

   False elevations (phantom hCG) may occur with patients who have human antianimal or heterophilic antibodies.

   Patients who have been exposed to animal antigens, either in the environment or as part of treatment or an imaging procedure, may have circulating antianimal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.

HUMAN LEUKOCYTE ANTIGEN (HLA) TESTING
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   Introduction

   The human leukocyte antigen (HLA) system, located on the short arm of chromosome 6 at position 6p21.3, is the major histocompatibility complex (MHC) in humans containing a cluster of genes related to immune system. The classical HLA spans 3.6 Mb and is subdivided into three regions: class I, class II, and class III. Each region contains numerous gene loci, including expressed genes, transcripts, and pseudogenes. Many HLA loci are among the most polymorphic genes within the human genome.