Test Limitations

As there is considerable biologic variability in microalbumin
excretion, it is recommended that all patients be evaluated for
microalbuminuria based on more than an isolated determination on a
single urine specimen (regardless of whether a timed or untimed
urine specimen is used). Reports indicate that intra-individual
biologic variability may be as high as 20 – 40% over the
course of a one-month period. Moreover, various physiologic and
pathologic factors are also known to potentially alter urinary
microalbumin excretion, including: strenuous exercise, diurnal
variation, pyrexia, urinary tract infection, menstruation,
pregnancy, acute diuresis or fluid overload, hypertension,
congestive heart failure, atherosclerosis, and postural
(orthostatic) proteinuria. These factors must be taken into
consideration when assessing patients for microalbuminuria, and
before any clinical decision is made concerning the need to
institute aggressive therapy (e.g., committing patients to a
long-term course of management with ACE
inhibitor antihypertensives).

It is strongly advised that all positive test results for
microalbuminuria be confirmed by follow-up testing on two
additional urine specimens, collected on separate occasions. If a
positive result is obtained by screening an untimed (random) urine
specimen, it is preferable that the confirmatory quantitation of
microalbumin be performed using timed (24 hour) urine collections.
If confirmatory test results are consistent with microalbuminuria,
and other physiologic or pathologic factors have been excluded as
potential causes, these findings may be considered indicative of
incipient nephropathy, and only then should aggressive therapy be
considered.