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February 2002
Q. When will a vaccine be available for hepatitis C?
A. The prospect for a traditional inactivated (killed)
or attenuated live hepatitis C virus vaccine is not immediate. Even
if every ongoing research study were to have the optimal outcome
and every regulatory and manufacturing process were on the fastest
track imaginable, no candidate vaccine could be approved and ready
for routine use within five years.
The principal scientific impediment is the propensity of HCV to
mutate and, thus, the inability of traditional vaccines to induce
protective immunity. Other limitations are the scarcity of chimpanzees,
the only animal model for studying HCV infection, and the absence
of an efficient HCV culture system for propagating HCV and testing
neutralizing antibodies. New approaches to vaccine development,
such as subunit, recombinant virus, or DNA vaccines, offer promise,
but it’s too early to predict their efficacy. Lastly, there is the
possibility that preventive immunity may not be necessary if a novel
vaccine could induce an immune response—even after HCV infection—that
would contain replication and prevent chronic infection and cirrhosis,
the major cause of HCV-related morbidity and mortality.
S. Gerald Sandler, MD
Professor of Medicine and Pathology
Director, Transfusion Medicine
Georgetown University Hospital
Washington, DC
Q. How valid are results on lipid profiles that are done
on ICU patients the day after admission? These patients usually
come in with chest pain. They are on IV solutions. They may have
been vomiting and in discomfort. Should we attach a disclaimer to
patient results that are done under other than "normal conditions"?
Or are these orders reasonable for patient care?
A. These questions are important ones and are oftentimes
neglected issues that are encountered almost every day in clinical
practice. Over the last decade we have seen significant improvements
in the methods, instruments, and calibration materials used to enhance
the accuracy of lipid and lipoprotein measurements in the clinical
laboratories. From an analytical standpoint, the manufacturers’
participation in the National Heart, Lung, and Blood Institute-Centers
for Disease Control and Prevention Standardization Program for lipids
and lipoproteins has resulted in their analytical testing systems
becoming certified because the accuracy of testing can be traced
to approved reference methods and calibrating materials.
Today, the biggest sources of error are preanalytical issues,
which can contribute to more than 50 percent of the total variation
that can influence the lipid and lipoprotein test results on serial
specimens collected from one person.1
The work of Smith et al2 demonstrated
that the average intra-individual variation for serum total cholesterol
is 6.1 percent; for LDL-cholesterol, 9.5 percent; for HDL-cholesterol,
7.4 percent; and for triglycerides, 22.6 percent. This makes it
difficult to classify coronary heart disease, develop appropriate
treatment strategies, and assess the efficacy of treatment. Ironically,
many of the intra-individual variations can be minimized or avoided.
It is wise to measure the blood lipids and lipoproteins only
during a patient’s steady state or while the patient is healthy
with no metabolic distress.3
Any patient in the hospital (especially if they are in the ICU,
CCU, ATU, or ER) should not be tested for lipids and lipoprotein
profiling. It is well established that during times of infections,
MI, stroke, surgical recovery, physical trauma, and other conditions
that do not represent a person’s normal metabolic state, the test
results are inaccurate and do not reflect the values obtained during
steady state. Furthermore, any untreated secondary causes of dyslipoproteinemia
should be first identified and then appropriately treated. They
could come from secondary conditions such as hormonal imbalances,
nephrotic syndrome, diabetes mellitus, or uncontrolled hypertension,
or from excessive weight change during a short period or major dietary
changes. The use of IV solutions compounds these problems by causing
further inaccuracies in the test results because of hemodilution
effects. Acute bouts of vomiting can cause dehydration and, thus,
hemoconcentration, which falsely elevates analyte values.
It is always best not to do any lipid and lipoprotein testing
for inpatients. One should safely wait four to six weeks after
hospital discharge to do measurements with patients who are in a
more stable metabolic state. Any behavioral or clinical sources
of variation should be noted and, if possible, eliminated before
the serum specimen is collected.4
The patient should maintain his or her normal lifestyle and should
not gain or lose weight around the time the blood specimen is collected.
The patient should also be advised to abstain from drinking alcohol
for two to three days before the specimen is collected. An overnight
fasting specimen is desirable for the measurement of the lipids
and lipoproteins when profiling the patient.
5
No medical decision should be based on a single measurement.
Because of the preanalytical sources of variation and the laboratory
analytical variation, at least two serial specimens should be measured
for the majority of individuals.
6,7
Cooper et al
8
calculated the total
percent error (NCEP total analytic error + biological variation)
for two separate measurements for total cholesterol to be 12.4 percent,
LDL-C to be 18.6 percent, for HDL-C to be 23.6 percent, and triglycerides
to be 37.0 percent. In other words, if the mean differences on the
repeated measurement values exceed the total percent error values,
another measurement should be taken.
Finally, if the patient’s specimen was analyzed, it would be prudent
to put a disclaimer on the inpatient’s inaccurate lipid and lipoprotein
test values because the patient was not in a stable metabolic condition
when the measurements were done.
References
1. Cooper GR, Myers GL, Smith SJ, et al. Blood
lipid measurements: variations and practical utility. JAMA.
1992;267: 16521660.
2. Smith SJ, Cooper GR, Myers GL, et al. Biological
variability in concentrations of serum lipids: sources of variation
among results from published studies and composite predicted values.
Clin Chem. 1993;39:1012-1022.
3. Naito HK. Cholesterol: How do we manage laboratory
and patient health data? In: Martin ML, Addison BV, Wagner WM, et
al, eds. 1989 Institute on Critical Issues in Health Laboratory
Practice: Improving the Quality of Health Management Through Clinician
and Laboratorian Teamwork. Wilmington, Del.: The Du Pont Co.;
1991:63-70.
4. National Heart, Lung, and Blood Institute.
Recommendations for improving cholesterol measurement: a report
from the Laboratory Standardization Panel of the National Cholesterol
Education Program. Bethesda, Md.: U.S. Department of Health and
Human Services, Public Health Service, National Institutes of Health,
1990; Publication No. 90-2964.
5. Executive summary of the third report of the
National Cholesterol Education Program expert panel on detection,
evaluation, and treatment of high blood cholesterol in adults (Adult
Treatment Panel III). JAMA. 2001;285: 2486-2497.
6. Cooper GR, Myers GL, Smith SJ, et al. Standardization
of lipid, lipoprotein, and apolipoprotein measurements. Clin
Chem. 1988;33:B95-B105.
7. Brookstein L, Gidding SS, Donovan M, et al.
Day-to-day variability of serum cholesterol, triglycerides, and
high-density lipoprotein cholesterol levels. Arch Intern Med.
1990;150:1653-1657.
8. Cooper RG, Smith SJ, Myers GL, et al. Estimating
and minimizing effects of biologic sources of variation by relative
range when measuring the mean serum lipids and lipoproteins.
Clin Chem. 1994;40:227-232.
Herbert K. Naito, PhD
Chief, Ancillary Testing and Satellite Facilities
Pathology and Laboratory Medicine Service
Louis Stokes Cleveland Veterans
Affairs Medical Center
Cleveland
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