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Labetalol Analysis with the TOXILAB#{174}
A Drug-DetectIon
System
To the Editor:
A false-positive result is due to either a limitation
of the method or
operator error. The recent report of an
interference in the TOXI-LAB screening procedure, when used for the analysis of labetalol, is an example of operator error and is avoidable by use of
procedures recommended by the manufacturer.
In a recent article (Clin Chem
1985;31:1250), false-positive
indices
were reported for amphetamines and
possibly trimethoprim
by the TOXILAB A System. TOXI-LAB is a commercially packaged, modified thin-layer chromatography system (1). Reference material, standards, training, and
customer consultation provided by the
manufacturer
help ensure the most
effective utilization of the system (1,2).
The system provides for drug detection
characteristics to be observed through
four different detection stages. After
presumptive identification, unknowns
are run alongside standards and their
Rf values and color characteristics are
compared. Identification is made after
detection characteristics
are demonstrated to be the same between unknown and standard in all four detection stages (2).
Even though the authors of the
aforementioned article observed that
detection characteristics were dissimilar in many respects, they reported the
presence of amphetamine,
methamphetamine, and trimethoprim.
Using
the TOXI-LAB procedure, we investigated the possibility of both false-positive findings and confusion among
these four analytes.
Patients’ urine specimens containing labetalol and metabolite were solicited from clinical laboratories. A specimen was also obtained that contained
amphetamine and methamphetamine.
These specimens were analyzed with
the System, with appropriate reference
standards. The results (Figure 1) demonstrate typical Rf values obtained for
standards and patients’ specimens containing (a) amphetamine and metharnphetamine and (b) labetalol. The Rf
values and colors are dissimilar
for
amphetamine, methamphetamine, and
labetalol. By following the manufacturer’s recommended
procedures for
comparing and interpreting
detection
characteristics,
it was obvious that
there was no match between labetalol
and any of the other three analytes
through the four stages. The color
characteristics for labetalol, amphetamine, and methamphetamine
are similar in Stage I but Rf values are dissimilar. In addition, Stage ifi fluorescences
for labetalol, trimethoprim,
and the
amphetamines are dissimilar.
Although this comparative analysis
demonstrates some similarity in color
detection characteristics between the
four analytes at Stage I, positive identification of substances dependsupon
certain factors: (a) unknowns must be
analyzed alongside known standards,
and (b) the unknown substance must
characteristics consistent with
that standard (color and Rf) throughout all four stages.
Because drug-screen test results directly influence patient care, the laboratory has a great responsibility
to
establish and maintain proficiency in
their analytical methods. By the use of
proper technique and recommended
procedures, the possibility of misinterpretations would be lessened, and the
quality of analyses greatly improved.
display
References
1. Martel PA, Jones DW, Rousseau RJ.
Applications of TOXI-LAB: a broad spectrum drug detection system in emergency
toxicology. Am Assoc Clin Chem TDM-T
1983;2:1-4.
2. TOXI-LAB Drug Detection System. Instruction Manual, cat. no. 181AB. Laguna
Hills, CA 92653: Analytical Systems, Division of Marion Laboratories.
3. TOXI-LAB Drug Compendium. Ibid.
A. Martel
Darrell Adams
Donald W. Jones
C. Michael O’Donnell
Patricia
Analytical Systems
Division of Marion Laboratories
Laguna Hills, CA 92653
Concentration
Fig. 1. TOXI-LAB
“A”detection characteristics
detectionstages,HV
Channel1, A-i standard:propoxyphene,methone, meperidine,codeine,morphine; A-2 standard:
diazeparn,cocaine,acetaminophen,
caffeine,nicotine,amphetamine,
methatsphetamine;amphetamine,
methamphetamine
(actualspecimen);4: labetalolandmetabolite(actualspedmen);5: labetalolstandard;6
trlmethop.im
standard
of Myelin Basic
Protein in Cerebrospinal Fluid in
Prognosis of Multiple Sclerosis
To the Editor:
Myelin basic protein (MBP), which
constitutes 30% of the total protein in
the myelin sheath of the central nervous system, is one of the best-characterized specific antigens. Acute experimental
TOXI-GRAM A, through all four
Inc.
allergic
encephalomyelitis,
a
model for human demyelinating
disease, has been experimentally
induced
by this protein. MBP is exclusively
located in the oligodendrocyte-myelin
complex and its determination in cerebrospinal fluid (CSF) by radioimmunoassay (RJA) is considered a marker for active demyelination (1).
The concentration of MBP in CSF is
increased in multiple sclerosis (MS)
during exacerbations of the disease,
but usually declines to within the normal range during remissions. Concentrations of MBP in CSF may also be
increased in non-MS neurological dieeases (2-8).
We measured MBP in CSF from 23
patients with definite MS and five with
probable MS, as classified by criteria of
Rose et al. (9).
Routine diagnostic investigations of
the patients included clinical evalua-
CLINICAL CHEMISTRY, Vol. 32, No.5, 1986 915
tion, CSF analysis, neurophysiological
studies, cranial computer tomography,
and nuclear magnetic resonance imaging. Lumbar puncture was performed
during acute relapses as a routine clinical diagnostic procedure, never only
for the purpose of measuring MBP. We
determined MBP with use of materials
from Diagnostic System Laboratories,
Inc., Webster, TX, with a double-antibody method. The lower sensitivity
limit was 0.5 g/L. The mean concentration of MBP in CSF from 33 control
subjects with no neurological disease
was 2.4 (SD 0.8) ig/L, range 1.0 to 4.3
Lg/L.
The values of MBP in CSF were
increased in 26 of the 28 MS patients.
These concentrations correlated signif
icantly (r = O.383;p <O.05;y = 16.4x +
10.9) with the Kurtzke disability status scale (10), but not with the duration of the illness (r = 0.073), the
severity score of neurological symptoms and signs in the relapse (r =
0.100), the duration of the relapse (r =
0.050), or the number of previous relapses (r = 0.161).
Assays of MBP in CSF have been
found to be useful although not specific
tests for the diagnosis of MS. There are
no previous reports about the prognostic value of these determinations. The
clinical course of MS patients is heterogeneous, and there are no criteria that
can predict the development of neurological sequelae, which makes difficult
the indication of aggressive treatment.
Our findings suggest that those patients with greater demyelination and
consequently higher concentrations of
MBP in CSF develop a higher incidence of late neurological dysfunctions.
This correlation, however, does not
exist for the dysfunctions that occur in
the immediate post-relapse period.
Determinations
of MBP in CSF of
patients with MS relapses can be useful in defining a prognostic index of the
disease. The patient with poor prognosis could, therefore, be identified and
treated accordingly. Further studies
about determinations
of MBP in patients with MS are needed to confirm
these results.
References
1. CohenSR, Heradon RM, McKhann GM.
Radioimmunoassay of myelin basic protein
in spinal fluid. An index of activedemyelination. N Engl J Med 1976;295:1455-7.
2. Whitaker JN, Lisak RP, Bashir RM, et
a!. linmunoreactive myelin basic protein in
the cerebrospinal fluid in neurological disorders. Ann Neurol 1980;7:58-64.
3. Cohen SR, Brooks BR, Herndon RM. A
diagnostic index of active demyelination.
Myelin basic protein in cerebroepinal fluid.
Ann Neurol 1980;8:25-31.
4. Biber A, Englert D, Dommasch D, Hem-
palK. Myelin basic protein in cerebrospinal
fluid of patients with multiple sclerosis and
other neurological diseases. J Neurol
1981225:231-6.
5. Warren KG, Latz I, McPherson A. CSF
myelin basic protein levels in acute optic
neuritis and multiple sclerosis. Can J
Neurol Sci 1983;10:235-8.
6. Matias-Guiu J, Ruibal A, Alvarez J, et
a!. Myelin basic protein in Fishersyndrome.
J Neurol 1985;232:263-4.
7. Matias-Guiu J, Martinez-Vazquez JM,
Ruibal A, Codina A. Cerebroapinal fluid
levels of myelin basic protein and creatine
kinase BB as index of active demyelination.
Acts Neurol Scand,in press.
8. Matias-GuiuJ, Martinez-Vazquez JM,
Ruibal A, et a!. Myelin basic protein and
creatine kinase BB isoenzyme as CSF
markers of intracranial tumors and stroke.
Acts Neurol Scand, in press.
9. Rose AS, Ellison GW, Myers LW, Tourtellotte WW. Criteria for the clinical diagnosis of multiple
sclerosis. Neurology
1976;26:20-2.
10. Kurtzke JF. Further notes on disability
evaluation in multiple sclerosis with scale
modifications. Neurology1965;15:654-61.
Jorge Matias-Guiu”5
Alvaro Ruibal2
Jose-Manuel Martinez-Vazquez3
Ramon Colomer
Agustin Codina’
‘Neurol. Service
2Lab. of Nuclear Med.
3Dept. of Med.
4Med. Oncol. Service
Hospital del Valle de Hebron
Universidad Autonoma de Barcelona
Barcelona, Spain
concentrations in plasma remain essentially unaltered (4). We have there-
fore established normal excretion patterns for RBP during uncomplicated
pregnancy and compared them with
RBP excretion in “normal” non-pregnant individuals.
We collected 24-h urine specimens
from 37 healthy pregnant women in
the first, second, and third trimesters
(up to 14, 28, and 40 weeks of gestation, respectively), and from 11 nonpregnant
healthy women, matched for
age. None of these persons had ingested any drug known to influence kidney
function for at least 10 days before the
specimen was collected. Samples were
immediately
frozen and stored at
-20 #{176}C
until assay. Results were expressed both as RBP excretion rates
and as RBP/creatinine ratios.
RBP excretion rates for the 24-h
specimens from the 11 non-pregnant
women had a median value of 50 ng/
min, and 95% confidence limits of 32 to
75 ng/min, and were not significantly
different from rates for a larger sample
of overnight-urine collections (n = 61;
median 53.6 ng/min; 95% confidence
limits: 11 to 189 nglmin; p >0.05) (2).
In contrast, the RBP excretion rate
was increased during normal pregnancy (Figure 1). The observed increases
were not enough to be significantly
different from the non-pregnant controls during the first or second trimester of pregnancy, but were pronounced
REP -
EXCRETION RATE
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p<O05
5Address for correspondence: Paseo San
P15
Gervasio 64, 6,08022-Barcelona, Spain.
Increased Urinary Excretion of
Retinol-Binding Protein during
Normal Pregnancies
To the Editor:
Recently, normal reference standards for retinol-binding protein (RBP)
in serum and urine, as measured by
radioiminunoassay,
were reported by
Beetham et al. (1). We have also developed a sensitive and precise RIA for
RBP in urine and have established
normal values that are similar to
theirs for non-pregnant individuals (2).
However, we would like to report increased urinary excretion of RBP during uncomplicated pregnancy.
Renal function, including the excretion of proteins, changes during pregnancy (3). Measurement of the increased excretion of proteins with a
relative molecular mass below 30 000
such as RBP, is considered to reflect
decreased tubular reabsorption if the
916 CLINICALCHEMISTRY,Vol.32, No. 5, 1986
I00
lOX
200
tOO
I
1
I
-I
i’s
2nd
3d
Fig. 1. Retinol-binding
proteinexcretionrates
as determinedwith 24-h urine specimens from
normal non-pregnant(M and pregnant women (1st first trimester; 2nd second trimester;
3,d thirdtrimester)