Abbott i-STAT 1 System Manual page 416

To convert a BUN result in mg/dL to a urea result in mmol/L, multiply the BUN result by 0.357. To convert a
urea result in mmol/L to a urea result in mg/dL, multiply the mmol/L result by 6. To convert a urea result in
mg/dL to a urea result in g/L, divide the mg/dL result by 100.
The i-STAT reference ranges for whole blood listed above are similar to reference ranges derived from serum
or plasma measurements with standard laboratory methods.
The reference range programmed into the analyzer and shown above is intended to be used as a guide
for the interpretation of results. Since reference ranges may vary with demographic factors such as
age, gender and heritage, it is recommended that reference ranges be determined for the population
being tested.
Clinical Significance
An abnormally high level of urea nitrogen in the blood is an indication of kidney function
impairment or failure. Some other causes of increased values for urea nitrogen include prerenal
azotemia (e.g. shock), postrenal azotemia, GI bleeding and a high protein diet. Some causes
of decreased values for urea nitrogen include pregnancy, severe liver insufficiency, overhydration
and malnutrition.
Performance Characteristics
The typical performance data summarized below were collected in health care facilities by health care
professionals trained in the use of the i-STAT System and comparative methods.
Precision data were collected in multiple sites as follows: Duplicates of each control fluid were tested in the
morning and in the afternoon on five days for a total of 20 replicates. The averaged statistics are presented
below.
Method comparison data were collected using CLSI guideline EP9-A.
collected in lithium heparin Vacutainer
of the specimen was centri fuged and the separated plasma was analyzed in duplicate on comparative
methods within 20 minutes of collection.
Deming regression analysis
table, n is the number of specimens in the data set, Sxx and Syy refer to estimates of imprecision based
on the duplicates of the comparative and the i-STAT methods, respectively, Sy.x is the standard error of the
estimate, and r is the correlation coefficient.*
Method comparisons will vary from site to site due to differences in sample handling, comparative method
calibration and other site specific variables.
*The usual warning relating to the use of regression analysis is summarized here as a reminder. For any analyte, "if the data are collected over a narrow
range, the estimate of the regression parameters is relatively imprecise and may be biased. Therefore, predictions made from these estimates may be
invalid." 4 The correlation coefficient, r, can be used as a guide to assess the adequacy of the comparative method range in overcoming this problem.
As a guide, the range of data can be considered adequate for r >0.975.
Precision Data (mg/dL)
Aqueous Control
Level 1
Level 3
BUN - 2
tubes and analyzed in duplicate on the i-STAT System. A portion
®
was performed on the first replicate of each sample. In the method comparison
4
Mean SD
52.8 0.76
5.5 0.45
Art: 714176-01Q
Venous blood samples were
3
%CV
1.4
8.2
Rev. Date: 15-Jul-16