Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1037 page)

   IAA testing must be performed before insulin therapy is initiated.

   Children at onset of type 1 DM are more commonly IAA positive than adults. Up to 80% of new–onset type 1 DM patients before the age of 5 years have IAA compared with only approximately 30% for adults.

JANUS KINASE-2 (JAK2) DNA MUTATION ASSAY
*

   Definition

   The
V617F
mutation in the
JAK-2
gene is associated with myeloproliferative disorders (MPDs). This mutation was found in more than 80% (up to 97%) of patients with polycythemia vera, in approximately 50% of patients with idiopathic myelofibrosis (IMF), 30–50% of patients with essential thrombocythemia (ET), and also in other rare MPDs.

   
Normal values:
an individual is negative for the
JAK-2
gene mutation when the frequency of wild-type and mutant alleles is 100% and 0%, respectively.

   Use

   Suspected polycythemia vera (PV; OMIM# 263300), idiopathic myelofibrosis (IMF; OMIM# 254450), or essential thrombocythemia (ET)

   Limitations

   The results of a genetic test may be affected by DNA rearrangements, blood transfusion, bone marrow transplantation, or rare sequence variations.

   Genetic causes of MPDs, other than the
V617F
mutation, will not be detected.

KLEIHAUER-BETKE TEST
^†

   Definition

   The Kleihauer-Betke test was developed to quantify fetal RBCs in maternal blood in order to determine the amount of Rh immune globulin that needs to be administered.

   The test is performed by treating maternal red cells on a thin slide smear with acid and then counterstaining the slide. Fetal hemoglobin is resistant to acid treatment so maternal cells will appear as “ghosts” while fetal cells will be pink.