Sorted By Test Name - Mayo Medical Laboratories

RTEP
89507
allergic reactions to insect venom allergens, drugs, or chemical allergens.
Interpretation: Detection of IgE antibodies in serum (Class 1 or greater) indicates an increased
likelihood of allergic disease as opposed to other etiologies and defines the allergens that may be
responsible for eliciting signs and symptoms. The level of IgE antibodies in serum varies directly with the
concentration of IgE antibodies expressed as a class score or kU/L.
Reference Values:
Class IgE kU/L Interpretation
0 Negative
1 0.35-0.69 Equivocal
2 0.70-3.49 Positive
3 3.50-17.4 Positive
4 17.5-49.9 Strongly positive
5 50.0-99.9 Strongly positive
6 > or =100 Strongly positive Reference values
apply to all ages.
Clinical References: Homburger HA: Allergic diseases. In Clinical Diagnosis and Management by
Laboratory Methods. 21st edition. Edited by RA McPherson, MR Pincus. New York, WB Saunders
Company, 2007, Chapter 53, Part VI, pp 961-971
Thymic Emigrants, Recent, CD4 and CD8 T-Cell Evaluation
Clinical Information: Naive T cells are generated in the thymus and exported to peripheral blood to
form the peripheral T-cell repertoire. The complement of recirculating naive T cells remains relatively
constant throughout life, despite constant antigenic stimulation and reduction of thymic output with age.
Recent thymic emigrants (RTEs) refer to those populations of naive T cells that have not diluted their
T-cell receptor excision circles (TREC) levels with cell division. Naive T cells are long-lived in the
periphery and this, combined with new production of RTEs from the thymus, maintains the peripheral
T-cell repertoire. RTEs express high levels of TRECs and undergo expansion and survival in an
antigen-independent manner, but still maintain their preselected T-cell repertoire.(1) In the CD4 T-cell
compartment, it has been shown that naïve CD45RA+ T cells coexpressing CD31 had higher levels of
TRECs compared to those T cells lacking CD31.(2) Similarly, in the CD8 T-cell compartment, it has been
shown that naive CD8+CD45RO-T cells coexpressing CD103 and CD62L had higher levels of TRECs
compared to T cells lacking CD103 and CD62L.(3) The higher levels of TREC indicate a more recent
thymic ontogeny, where the TRECs are not diluted by peripheral cell division. It has been shown that
CD31+CD4+ T cells continue to possess high levels of TREC despite an age-related tenfold reduction
from neonatal to older age.(4) CD4 RTEs (CD31+CD4+CD45RA+) have longer telomeres and higher
telomerase activity, which, along with the increased TREC levels, suggest a population of T cells with
low replicative history.(4) CD31+CD4+ T cells are an appropriate cell population to follow to evaluate
thymic reconstitution in lymphopenic children post-hematopoietic stem cell transplant (HSCT).(4) A
Mayo study showed that the CD31 marker correlates with TREC-enriched T cells across the spectrum of
age and correlates with thymic recovery in adults after autologous stem cell transplantation.(5) CD31+
CD4 RTEs have also been used to evaluate T-cell homeostatic anomalies in patients with
relapsing-remitting multiple sclerosis (RRMS).(6) There is an age-related decline in the numbers of
CD103+CD62L+ CD8 RTE, which also can be precipitated by thymectomy or loss of thymic function.(5)
Additionally, these cells are quite short-lived in the periphery.(3,5) A Mayo study showed that in adults
over the age of 20 there is no linear correlation between CD8 RTE expressing CD103 and CD62L and
TREC levels, suggesting that homeostasis in the CD8 T-cell compartment is probably maintained more by
peripheral expansion than by thymic output.(5) This concept may be corroborated by the fact that CD8
T-cell counts recover numerically more rapidly post-HSCT than CD4 T cells, resulting in a skewed
CD4:CD8 ratio for several months to 1 year posttransplant, and that increase in CD4 T-cell counts
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