Maternal AFP and fetal karyotyping
S-adenosylhomocysteine
vs. homocysteine as a cardiac marker
Elevated plasma total homocysteine (tHcy) has been identified as
an independent risk factor for vascular disease. The underlying
relationship between increased homocysteine levels and vascular
disease, however, is somewhat controversial. Some have suggested
that elevated plasma homocysteine levels are an effect rather than
a cause of atherosclerotic disease. Others have argued that hyperhomocysteinemia
is a proximate risk factor that provokes the acute event. In any
case, the use of plasma tHcy levels as an indicator of vascular
disease risk is widespread. There is considerable overlap in values
for patients with vascular disease and control subjects such that
marked elevations are necessary to revise an individual's risk of
developing vascular disease. S-adenosylhomocysteine is a metabolic
precursor of homocysteine produced in the body. It is formed by
methyltransferase reactions involving S-adenosylmethionine (SAM)
as the methyl donor. Some have suggested that the effect of homocysteine
on vascular endothelial function may be due to the production of
S-adenosylhomocysteine from homocysteine resulting from the action
of the enzyme adenosylhomocysteinase, or SAH hydrolase. The authors
became interested in measuring plasma SAH levels to determine whether
it might be more informative than plasma tHcy for determining the
risk of vascular disease. They measured plasma tHcy, SAH, SAM, creatinine,
folate, and vitamin B12 in 30
patients with proven cardiovascular disease and in 29 age- and sex-matched
control subjects. Values for folate and vitamin B12
did not differ significantly between the groups. The creatinine
values were 110 µmol/L on average for patients and 97 µmol/L on
average for controls. The homocysteine values were 12.8 µmol/L on
average for patients and 11.0 µmol/L on average for controls. The
SAH values were 40 nmol/L on average for patients and 27 nmol/L
on average for controls. The P value for this difference
was highly significant at 0.0021. The authors concluded that plasma
SAH appears to be more sensitive than homocysteine as an indicator
of the difference between patients with cardiovascular disease and
control subjects. Total homocysteine and SAH levels were significantly
correlated with plasma creatinine in patients.
Kerins DM, et al. Plasma S-adenosylhomocysteine
is a more sensitive indicator of cardiovascular disease than plasma
homocysteine. Am J Clin Nutr. 2001;74:723-729.
Reprints: C. Wagner, Dept. of Biochemistry and Medicine, Vanderbilt
University School of Medicine, 620 Light Hall, Nashville, TN 37232-0146;
conrad.wagner@vanderbilt.edu
Measuring LDL-cholesterol:
calculation vs. homogeneous assay
In the National Cholesterol Education Program (NCEP) Adult Treatment
Panel III (ATPIII) guidelines, diagnostic and treatment efforts
in cardiac risk assessment are focused on total cholesterol and
low-density lipoprotein cholesterol. Therapy is intended to lower
LDL-C values below a target value. These target values depend on
a number of independent risk factors. Accurate and standardized
measurements of LDL-C are therefore necessary to reliably classify
patients. LDL-C is most commonly determined using the Friedewald
formula, which estimates LDL-C from measurements of total cholesterol,
triglycerides, and high-density lipoprotein cholesterol. This calculation,
however, has limitations. Direct methods for measuring LDL-C also
have limitations for general use. Recently, however, a new generation
of homogeneous assay methods capable of full automation has been
introduced. It uses specific reagents of various types to selectively
expose and directly measure the cholesterol associated with LDL.
The authors critically reviewed the literature on the new homogeneous
assays. They concluded that the new assays seem to conform to NCEP
requirements for LDL-C testing with regard to precision (coefficients
of variation of less than four percent) and accuracy (bias of less
than four percent) in specimens collected from nonfasting individuals.
All five of the available homogeneous assays have been certified
by the Cholesterol Reference Methods Laboratory Network. These assays
appear to better classify individuals into NCEP cutpoints than the
Friedewald calculation. Limited evaluations to date, however, raise
questions about the reliability and specificity of the assays. Yet
evidence supports using the homogeneous assays for LDL-C as a supplement
to the Friedewald calculation in those cases where the calculation
is known to be unreliable—for example, with triglycerides
of more than 4,000 mg/L.
Nauck M, Warnick GR, Rifai N. Methods for measurement
of LDL-cholesterol: a critical assessment of direct measurement by
homogeneous assays versus calculation. Clin Chem. 2002;48:236-254.
Reprints: Matthias Nauck, University Hospital Freiburg, Dept.
of Clinical Chemistry, Hugstetter Strasse 55, D-79106 Freiburg i.Br.,
Germany; manauck@med1.uk1.uni-freiburg.de
Hospital deaths
potentially associated with nosocomial infection
Various studies of nosocomial infection have placed the incidence
risk at between four and nine cases per 100 discharges. Nosocomial
infection is a leading cause of death in the United States and Europe.
It has been estimated that as many as one percent of all patients
with a nosocomial infection die as a direct result of the infection
and that nosocomial infections contribute to the death of 2.7 percent
of patients admitted to hospitals. Few, if any, studies have used
population attributable risk as a measure of the effect of nosocomial
infections on the rate of intrahospital death. The authors conducted
a study to determine the fraction of hospital deaths associated
with nosocomial infection. They examined the association for all
nosocomial infections and for different types of nosocomial infections.
The authors used a matched case-control study design in an 800-bed
tertiary care teaching hospital. All patients older than 14 years
who were admitted to the hospital between Jan. 1, 1990 and Jan.
1, 1991 were eligible. The authors recorded the 524 consecutive
deaths that occurred in the hospital, which constituted the case
group. For each case, a control patient was matched on primary admitting
diagnosis and admission date. The population attributable risk (PAR)
was adjusted for age, gender, service, severity of illness, length
of stay, and quality of the medical record. The proportion of hospital
deaths that potentially could be attributed to nosocomial infection
was estimated from this PAR. The PAR for all nosocomial infections
was estimated to be 21.3 percent. The greatest proportion of deaths
that were potentially associated with nosocomial infections was
observed in patients with only a single infection and bacteremia
or sepsis. The PAR for a single infection was 15 percent and for
bacteremia or sepsis was 7.7 percent. The authors concluded that
nosocomial infections are associated with a large proportion of
intrahospital deaths.
Garcia-Martin M, Lardelli-Claret P, Jimenez-Moleon
J, et al. Proportion of hospital deaths potentially attributable to
nosocomial infection. Infect Control Hosp Epidemiol. 2001;22:708-714.
Reprints: Miguel Garcia-Martin, Departmento de Medicina Preventiva
y Salud Publica, Facultad de Medicina, Universidad de Granada, 18071
Granada, Spain
Blood cell count
changes in blood stored at room temperature
Blood specimens submitted for a complete blood cell count and differential
leukocyte count may be delayed in transit. When such a delayed specimen
arrives in the lab, staff must decide whether to accept it. To make
such a decision, laboratorians need to be familiar with the changes
known to occur in blood specimens during storage. Information regarding
the suitability of specimens older than one day for various lab
tests, including the CBC and automated differential, is fairly scarce
in the recent literature. The authors attempted to delineate changes
that occur in various parameters of the automated CBC and differential
during storage of blood at room temperature for several days. They
performed a CBC and automated white-cell differential count using
a Coulter Gen.S on 40 K3 EDTA-anticoagulated
blood specimens once a day for three to seven days. The specimens
were stored at room temperature during the study and results were
tabulated in an Excel spreadsheet. The hemoglobin, red blood cell
count, and mean corpuscular hemoglobin were stable for the duration
of the study, which was seven days. The white blood cell count was
stable for at least three days and up to seven days if the count
was within or above the normal range. Platelet count was stable
for four days and up to seven days if the count was within or above
the normal range. The mean corpuscular volume, mean platelet volume,
hematocrit, and RBC distribution width increased, and the mean corpuscular
hemoglobin concentration decreased from day two onward. Among the
differential parameters, the relative percentages and absolute numbers
of neutrophils, lymphocytes, and eosinophils tended to increase,
whereas those of monocytes trended downward over time. There was
no appreciable change in basophils, although data were limited.
Gulati GL, Hyland LJ, Kocher W, et al. Changes
in automated complete blood cell count and differential leukocyte
count results induced by storage of blood at room temperature. Arch
Pathol Lab Med. 2002;146:336-342.
Reprints: Dr. Gene L. Gulati, 307 Pavilion Bldg., Thomas Jefferson
University Hospital, 125 S. 11th St., Philadelphia, PA 19107; gene.gulati@mail.tju.edu
HIV drug susceptibility
testing
Human HIV-1 infections treated with antiretroviral drugs that are
selected on the basis of drug-resistance testing have been associated
with improved virologic responses. A number of phenotypic and genotypic
assays are being used to monitor drug resistance in HIV. The genotypic
assays detect resistance-related mutations and provide indirect
evidence of drug resistance, whereas the phenotypic assays measure
the ability of the virus to replicate in the presence of a drug
and are therefore a direct measurement. The IC50,
or inhibitory dose for 50 percent of virus replication for a drug-susceptible
reference virus, is the baseline used to measure reductions in drug
susceptibility. The conventional phenotypic assays require isolating
HIV-1 from blood mononuclear cells or plasma. This adds labor time
and cost. Newer phenotypic assays circumvent this requirement for
viral isolation. The authors evaluated the correlation between the
results of drug-resistance testing assays for two commercial phenotypic
assays—the Antivirogram and PhenoSense HIV assays. They analyzed
HIV-1 isolates from 50 plasma specimens for phenotypic susceptibility
to reverse transcriptase (RT) inhibitors and protease (PR) inhibitors
using the Antivirogram and PhenoSense assays. Twenty of the specimens
came from drug-naïve persons who had seroconverted and 30 were from
patients who were sources of occupational exposures to HIV-1. Sixteen
of the specimens in this latter group were from drug-experienced
patients. The results of the phenotypic assays were characterized
as sensitive or reduced susceptibility on the basis of cutoff values
established by the manufacturers. Data for 12 to 15 drugs were available
by both assays for 38 specimens and represented 529 pairs of results.
The two data sets have a 91.5 percent concordance by phenotypic
category. The 45 discordant results were distributed randomly among
26 specimens and included 28 results which were within a two-fold
difference of the assay cutoff values. None of the discordant results
were associated with primary resistance mutations that predicted
high-level resistance—greater than 20 fold. The discordant
results were distributed equally among specimens from the drug-experienced
and drug-naïve subjects. The results were slightly higher for protease
inhibitors than for nonnucleoside or nucleoside reverse transcriptase
inhibitors. The authors concluded that the two assays correlate
well, despite the use of different testing strategies.
Qari SH, Respess R, Weinstock H, et al. Comparative
analysis of two commercial phenotypic assays for drug susceptibility
testing of human immunodeficiency virus Type 1. J Clin Microbiol.
2002;40:31-35.
Reprints: HIV and Retrovirology Branch, CDC, MS G-19, 1600 Clifton
Rd., Atlanta, GA 30333; wmh2@cdc.gov
A DNA-based assay
for detecting prostate cancer in urine sediment
Promotor hypermethylation of the glutathione-S-transferase P1 (GSTP1)
is an epigenetic DNA alteration that has been identified as the
most common DNA alteration in prostate cancer. This alteration is
absent in nonmalignant tissue. GSTP1 inactivation is being increasingly
implicated as an early event in prostatic carcinogenesis. Hypermethylation
of GSTP1 promoter can be detected by methylation-specific polymerase
chain reaction. This method is capable of identifying hypermethylated
alleles from tumor DNA within 104-
to 105-fold excess amounts of
unmethylated alleles from normal DNA. This situation may be encountered
in analyzing urine samples for shedded prostate cancer cells in
larger amounts of urothelial, prostatic, and other benign cells.
The authors investigated the diagnostic potential of methylation-specific
PCR as a DNA-based approach for molecular detection of prostate
cancer in urine sediment. They used bisulfite treatment followed
by methylation-specific PCR to detect GSTP1 promotor hypermethylation
in DNA isolated from urine sediments obtained after prostatic massage
of men with and without prostate cancer. GSTP1 promoter hypermethylation
was demonstrated in the sediments of one of 45 patients diagnosed
with benign prostatic hyperplasia, two of seven patients with prostatic
intraepithelial neoplasia, 15 of 22 patients with early intracapsular
cancer, and 14 of 18 patients with locally advanced or systemic
prostate cancer. This resulted in a calculated specificity of 98
percent and a calculated overall sensitivity of 73 percent for detecting
prostate cancer. The authors concluded that urinalysis for GSTP1
promoter hypermethylation may be a sensitive and specific marker
for molecular detection of prostate cancer, including early stage
cancer.
Goessl C, Müller M, Heicappell R, et al. DNA-based
detection of prostate cancer in urine after prostatic massage. Urology.
2001;58:335-338.
Reprints: Dr. Carsten Goessl, Dept. of Urology, Benjamin Franklin
Medical School, Free University of Berlin, Hindenburgdamm 30, Berlin,
1220, Germany
Use of pneumatic
tube systems with blood gas specimens
Pneumatic tube systems are used widely in hospitals to rapidly deliver
specimens to the clinic lab. The use of such systems is predicated
on the notion that there are no significant effects on analytes.
In response to a recent report of perturbations in pO2
values subsequent to air contamination, the authors decided to study
this issue in their hospital. They performed a three-stage study.
In the first stage, consecutive samples were drawn in duplicate
from patients during a two-week period. One of the samples was analyzed
immediately in the intensive care unit using point-of-care methodology.
The second sample was capped and sealed in a gas-tight plastic envelope
and hand-delivered to the lab for analysis. In the second phase
of the study, consecutive samples were drawn in duplicate from patients
during a two-week period. One of these samples was analyzed immediately
in the ICU and the second was capped and sealed in a gas-tight plastic
envelope and sent to the lab via the pneumatic tube system. In the
third phase, consecutive samples were drawn in triplicate from patients
during a two-week period. One of the samples was analyzed on the
floor and the remaining two samples were capped and sealed in separate
gas-tight plastic envelopes. One of the latter was sent to the lab
via the pneumatic tube system using the conventional canister and
the second was sealed inside a pressure-tight container and sent
to the lab via the pneumatic tube system inside the conventional
canister. The authors found that the specimens that were sent via
the pneumatic tube system tended to have significant alterations
in pO2 values, which was not seen
with the other modes of transport. There was no effect on pCO2
and pH values. Use of the pressure-sealed container abolished the
negative effect on pO2values
that was otherwise observed. The authors recommended that samples
for blood gas analyses be transported in a pneumatic tube system
using a pressure-sealed container to avoid artefacts in the pO2.
Collinson PO, et al. Changes in blood gas samples
produced by a pneumatic tube system. J Clin Pathol. 2002;55:105-107.
Reprints: Dr. P.O. Collinson, Dept. of Clinical
Biochemistry, 2nd floor - Jenner Wing, St. George's Hospital, Blackshaw
Rd., London, SW17 OQT, United Kingdom; poctrop@poctrop.demon.co.uk
Maternal AFP and
fetal karyotyping
More than 25,000 amniocenteses per year are estimated to be performed
in the United States for the indication of an elevated maternal
serum a-fetoprotein (AFP). It is common practice to send the amniotic
fluid specimen obtained at the time of the procedure for not only
AFP amniotic fluid levels but also for fetal karyotyping. Some studies
have suggested, however, that obtaining a fetal karyotype routinely
may not be necessary because of the relatively low incidence of
chromosomal abnormalities in this subset of patients. The authors
studied whether it is necessary to obtain a fetal karyotype on all
patients undergoing amniocentesis for an elevated maternal serum
AFP. They collected data retrospectively on patients under age 35
who were undergoing amniocentesis for elevated serum AFP. This included
537 patients with maternal serum AFP values greater than 2.5 multiples
of the median. Of 509 patients in the group with normal amniotic
fluid AFP levels, 505 had a normal karyotype (specificity, 94.9
percent; negative predictive value, 99.2 percent). Of the 28 patients
in the group with an elevated amniotic fluid AFP, one had an abnormal
karyotype (sensitivity, 20 percent; positive predictive value, 3.6
percent). The authors concluded that fetal chromosomal analysis
of amniotic fluid amniocytes need not be performed routinely for
patients who have a normal level of amniotic fluid AFP. The fetal
karyotype is, however, recommended for those patients with an elevated
amniotic fluid AFP.
Gonzalez D, Barrett T, Apuzzio J. Is routine fetal
karyotyping necessary for patients undergoing amniocentesis for
elevated maternal serum a-fetoprotein? J Matern Fetal Med.
2001;10:376-379.
Reprints: J. Apuzzio, Dept. of Obstetrics, Gynecology
& Women’s Health, University of Medicine & Dentistry of New Jersey,
New Jersey Medical School, 185 S. Orange Ave., Newark, NJ 07103-2714;
apuzzijj@umdnj.edu