Expected Values - Siemens IMMULITE 2000 TBG Manual Del Usuario

Assay Procedure
Note that for optimal performance, it is
important to perform all routine
maintenance procedures as defined in the
IMMULITE 2000 Systems Operator's
Manual.
See the IMMULITE 2000 Systems
Operator's Manual for: preparation, setup,
dilutions, adjustment, assay and quality
control procedures.
Recommended Adjustment Interval:
1 week.
Quality Control Samples: Use controls
or serum pools with at least two levels
(low and high) of TBG.
Calculation of TBG Saturation
Index
The TBG Saturation Index (TBG-SI)
represents the fractional occupation of
TBG binding sites by T4, expressed as a
13
percent. This is a natural measure since
TBG has a single binding site for thyroid
hormones, with a higher affinity for T4
than for T3; and T4 circulates at a much
higher concentration than T3.
The TBG-SI is defined as 100 times the
molar ratio of total T4 to TBG:
Total T4 (nmol/L)
TBG-SI =
TBG (nmol/L)
The definition makes the TBG–SI
independent of the units used to report
total T4 and TBG results, since it requires
putting both results into the same
concentration units (e.g. nmol/L) before
computing their ratio. For example, given
total T4 and TBG concentrations
expressed in mass units of µg/dL and
µg/mL, respectively, multiply the T4 result
by 12.87 to convert from µg/dL to nmol/L,
multiply the TBG result by 18.5 to convert
µg/mL to nmol/L, then multiply by 100 as
in the formula above. Alternatively,
multiply the T4/TBG ratio in the mass units
indicated by (12.87 / 18.5) x 100 = 69.5:
Total T4 (µg/dL)
TBG-SI =
TBG (µg/mL)

Expected Values

Based on its relationship to IMMULITE
TBG (see Method Comparison), the assay
4
can be expected to have essentially the
same reference ranges.
A reference range study was performed
with IMMULITE TBG kit on 75 serum
samples. These were obtained from adult
men and nonpregnant women in good
health; all samples had normal total T4
and free T4 index (FT4I) levels. The TBG
results showed an absolute range of
a central 95% range of 14 to 31 µg/mL,
and a median of 19 µg/mL. This is in good
agreement with the literature, which
indicates a reference range of 15 to
34 µg/mL for TBG as determined by RIA.
TBG Saturation Index (TBG–SI) values
were calculated for these 75 samples,
using results obtained with the IMMULITE
TBG and IMMULITE Total T4 kits. The
TBG–SI values ranged from 17 to 39%
(central 95%), with a median of 27%. This
is likewise in agreement with the literature,
which indicates a reference range of 2 to 5
for the T4/TBG ratio calculated as T4 (in
µg/dL) times 10 divided by TBG (in
µg/mL);
14 to 35% for the TBG–SI.
Twenty-four samples obtained from
women in various stages of pregnancy,
when assayed by the IMMULITE TBG kit,
yielded TBG levels ranging from 27 to
× 100
66 µg/mL, with a median of 43 µg/mL).
The literature suggests 47 to 59 µg/mL as
the range of TBG values expected for
pregnant women in the third trimester.
Consider these limits as guidelines only.
Each laboratory should establish its own
reference ranges.
Limitations
Many physiological, pharmacological,
pathological, and genetic factors affect the
interpretation of TBG results. (Refer to the
Summary and Explanation of the Test
section.)
Increased TBG levels may occur with
estrogen therapy (including oral
contraceptives), pregnancy, some cases
× 69.5
of hepatitis, and as an inherited condition.
Decreased TBG levels may be due to the
presence of androgens or anabolic
steroids; nephrotic syndrome; severe liver
disease; increased protein catabolism with
fever, wasting diseases, surgery, stress,
and as an inherited condition.
13 to 39 µg/mL,
8
this corresponds to a range of
IMMULITE 2000 TBG (PIL2KTB-18, 2010-07-07)
8
8
9,10