Sepsis makes for a particularly perfect villain: It's notorious for taking healthy people to death's door in short order and has outwitted the best of medical minds trying to unravel its baffling trail of clues over the years.
Work is moving forward, however, in linking biomarkers
to treatments for sepsis, though the advances come slowly and not without
the usual stumbling blocks and controversy.
Currently, there are two FDA-approved biomarkers specifically
for sepsis. One is Spectral Diagnostics' Endotoxin Activity Assay, or
EAA, which measures the level of bioactive endotoxin in a patient's blood,
with results in about 30 minutes. The FDA cleared the EAA in 2003 under
a de novo classification to help identify patients at risk for progressing
to severe sepsis within 24 hours of ICU admission.
The other is Berlin-based Brahms Diagnostics' procalcitonin,
or PCT, test, a biomarker that can help flag bacterial infection in sepsis.
BioMérieux last month received FDA 510(k) clearance
to market the Vidas Brahms PCT test in the United States to evaluate patients
within the first 24 hours of their ICU stay. Brahms has a PCT test under
FDA review now with potential applications for both the ICU and emergency
department, says Jonas Leichtner, director of marketing for Brahms Diagnostics
USA, Annapolis, Md.
Daniel Levine, PhD, director of the Iris & B. Gerald
Cantor Clinical Research Laboratory at The Rogosin Institute and associate
professor of biochemistry at Weill Medical College of Cornell University,
New York, NY, thinks the EAA may help in determining the appropriate intervention
in the ICU "or give you a way to figure out potentially who can go to
a step-down unit, which is less costly."
The Endoxotin Activity Assay has been available for
about four years, and more has become known about endotoxin and sepsis
in that time. It may be that "the mediator of sepsis," says Spectral president
and CEO Paul Walker, MD, PhD, is endotoxin translocated from gram-negative
bacteria that normally inhabit the gastrointestinal tract.
That is, a person with sepsis can have endotoxin in
his or her blood without having a gram-negative infection. Edward Abraham,
MD, professor and chair of the Department of Medicine at the University
of Alabama at Birmingham, says, "Gram-positive infection can lead to elevated
endotoxin in the blood because as the person becomes sicker, his or her
intestines become more permeable, releasing waves of endotoxin into the
blood." Infection with viruses or even a parasite, such as malaria, can
have the same effect.
"An endotoxin level in the setting of sepsis
is very high," exceeding 0.6 EAA units, Dr. Walker notes. Using the EAA,
Spectral has found that a normal value is about 0.26 EAA units. "The gray
area is between 0.4 to 0.6 EAA units," he says.
Spectral is analyzing data now from a study conducted
in the United States that looked at EAA levels in patients in the emergency
department, though Dr. Walker says it's too early to release the results.
Thus far, the assay hasn't caught on in the United
States, says Debra Foster, director of Spectral's sepsis program. The
test, which doesn't have Medicare or private payer approval for reimbursement,
she notes, costs less than half of what a blood culture costs.
Dr. Levine, who along with colleagues is doing research
with endotoxin in an area outside of sepsis, says his experience in talking
to physicians is that they are hesitant to integrate a new biomarker into
their protocols unless it adds substantially to the tools they already
have in place.
But Robert A. Balk, MD, director of pulmonary and critical
care medicine at Rush University Medical Center, Chicago, attributes the
assay's slow uptake in the United States to its nonspecificity. "It's
quite sensitive to picking up endotoxin, but endotoxin may be present
for a variety of reasons in critically ill people…" Periods of poor gut
perfusion or altered mucosal barrier function, he notes, can result in
translocation of the endotoxin or gram-negative organisms into the circulation.
And that could lead to a false-positive EAA result indicating sepsis.
Spectral's Foster agrees that gut hypoperfusion can
be a source of endotoxemia. Yet endotoxemia is an important risk factor
for a patient having sepsis, she says, which is the essence of the company's
FDA claim for the test. And as with all laboratory tests, Foster adds,
the physician has to consider the result within the context of a particular
patient and, if appropriate, intervene with early goal-directed therapy
Dr. Walker says Spectral has a preliminary hypothesis
with data suggesting that adequate fluid therapy in sepsis may stop endotoxin
from leaking out of the gut. "Adequate perfusion prevents organ dysfunction,
and that is a very important component of treatment." An article in the
November 2007 issue of Shock, he says, shows "fluctuating levels
of endotoxin in the first three days in the ICU is very deleterious to
the patient and is associated with multiple organ dysfunction" (Klein
D, et al. Shock.
If clinicians could identify patients with elevated
or rising endotoxin levels, Dr. Walker says, they could treat them aggressively
with fluids. "There may be a window of opportunity to get rid of endotoxin.
Once the cascade gets downstream, it's hard to pull the person out."
The emergence of anti-endotoxin therapies offers new
opportunities for combining the EAA with treatment. For example, in Japan
and Europe, Dr. Walker says, there is an approved method for removing
endotoxin from the blood: a dialysis process using a column, Toraymyxin
(Toray Industries, Tokyo), coated with the antibiotic polymyxin B, which
binds to endotoxin, stripping it out of the patient's blood.
David Klein, MD, coauthor of the November Shock
article on endotoxin and a critical care medicine physician at the University
of Toronto, notes there are anti-endotoxin therapies in clinical trials
in the U.S., which, once approved, could provide a "pull effect" for use
of the EAA.
Eisai Medical Research Inc., Ridgefield Park, NJ, is
enrolling patients now in a phase three clinical trial to test an anti-endotoxin
medication for severe sepsis. The investigational drug, eritoran tetrasodium,
is believed to block the ability of endotoxin to activate toll-like receptor
4 (TLR4), says Mel Lynn, PhD, Eisai's associate vice president and global
head of the sepsis and anti-infectives therapeutic area. "TLR4 is thought
to play an important role in the course of severe sepsis, and when activated
by endotoxin, can trigger a cascade of inflammatory responses."
The idea behind using procalcitonin—the only
other FDA-cleared test for sepsis—is that it can help physicians
identify which patients have clinically relevant bacterial infections
so appropriate antibiotics can be initiated sooner.
An article published in Critical Care Medicine last
year showed that adult patients with septic shock who received effective
antimicrobial therapy within the first hour of documented hypotension
had a survival rate of 79.9 percent. Each hour of delay in antimicrobial
administration over the ensuing six hours was associated with an average
decrease in survival of 7.6 percent (Kumar A, et al. Crit
Care Med. 2006;34:1589-1596).
Elevated PCT raises the index of suspicion that a patient
has a bacterial infection causing sepsis. Herb Steward, executive vice
president of BioMérieux, which is offering the PCT test on its Vidas and
mini-Vidas immunoassay platforms with results available in 20 minutes,
explains that PCT is found in the thyroid gland and is not normally present
in the bloodstream of a healthy person. Multiple organs in the body release
PCT when there is a systemic bacterial infection.
Typically in ICU patients, says Brahms Diagnostics'
Leichtner, a cutoff of 0.5 ng/mL indicates a low risk of severe bacterial
infection, whereas values of about 2.0 ng/mL are a clear indication of
severe bacterial infection. In between, he says, is a gray zone.
In certain situations, Steward adds, PCT can rise without
"any infectious aggression." Examples include trauma, burns, major surgery,
and prolonged or severe cardiogenic shock. But the PCT levels usually
return to normal rapidly. The physician can in such cases monitor the
patient's PCT levels, and levels that don't recede may be an indication
of bacterial infection, he says.
As a test for sepsis, PCT isn't without its detractors.
A meta-analysis published in March by Benjamin Tang, MD, and colleagues
at the University of Sydney, Nepean Hospital, in Australia, found that
the test could not "reliably differentiate sepsis from other non-infectious
causes of systemic inflammatory response syndrome in critically ill adult
patients" (Tang B, et al. Lancet
Infect Dis. 2007;7:210-217).
In a response to the study's findings published in
the same journal, Mueller, et al. (2007;7:498-499) point out
that PCT as a marker for serious bacterial infection has been studied
in both observational and intervention trial designs. They write, "A gold
standard to differentiate infectious from non-infectious causes in patients
with SIRS [systemic inflammatory response syndrome] does not exist, and
therefore all observational studies are prone to a potential bias."
Some studies use the physician's decision to order
blood cultures or to prescribe antibiotics as the definition for bacterial
infection, Leichtner says. Other studies rely on infectious disease specialists
to identify bacterial infection or look back retrospectively at laboratory
data and other findings. Thus, he says, such studies may not be comparing
apples to apples.
By contrast, intervention trials involve use of PCT
to guide which patients require antimicrobial therapy. The thinking is
that patients with a low PCT do not have a serious bacterial infection
and can go without antibiotics. "For PCT," Leichtner says, "there are
several randomized controlled trials that have successfully evaluated
this concept in patients with low respiratory tract infections."
Rush University's Dr. Balk believes that combining
PCT with polymerase chain reaction assays and clinical assessment may
more quickly identify patients with sepsis due to bacterial infection,
including gram-negative infection. "You would then initiate early antibiotic
therapy based on the likely organism(s) and your knowledge of the antibiogram"
of the institution, community, or both, he says.
BioMérieux sees PCT along with molecular infectious
disease testing as a potentially winning combination for sepsis. At this
year's American Society for Microbiology meeting, the company announced
the exclusive distribution agreement with AdvanDx for PNA FISH, molecular-based
tests that make it possible for labs to more rapidly identify infectious
organisms directly from blood cultures.
Margie Morgan, PhD, a microbiologist at Cedars-Sinai
Medical Center, Los Angeles, says PNA FISH, which "is easier to perform
and less expensive than PCR," is a staining technique performed on positive
blood cultures that can in 2.5 hours identify Staphylococcus aureus,
coagulase-negative staph, enterococcus, Candida albicans, and
BioMérieux signed an exclusive deal with Cepheid to
develop a line of sepsis test products on Cepheid's GeneXpert platform.
The GeneXpert system's real-time PCR amplifies and detects DNA sequences
associated with a microorganism. The test menu is scheduled to be launched
in Europe in 2010 and in the United States in 2011. Cepheid will manufacture
the assays, and BioMérieux will distribute them on an exclusive worldwide
basis, Steward says. The product menu consists of bacterial and fungal
identification assays and a series of genetic markers for antibiotic resistance.
So far, there is only one specific sepsis treatment,
Eli Lilly's Xigris (activated protein C or drotrecogin alfa), approved
by the FDA in 2001 for patients with severe sepsis at high risk for death.
Lilly has a study underway, RESPOND, that involves measuring serial protein
C levels in patients taking Xigris to evaluate their therapeutic response
to the drug.
Lilly is conducting the study with Inverness-owned
Biosite Inc. in an effort to develop a point-of-care protein C test that
could be used to adjust the dosage and duration of Xigris treatment based
on a patient's protein C levels, says Mark Williams, MD, medical director
for Xigris global brand development at Eli Lilly and Company, Indianapolis.
Sepsis patients with a lower protein C level have been
shown to have a higher risk of death. And, says John Brandt, MD, clinical
research physician/pathologist at Eli Lilly, "Administration of Xigris,
a recombinant activated protein C, has been associated with a more rapid
increase in the levels of endogenous protein C." Sepsis patients whose
endogenous protein C levels return to normal appear to have higher rates
The hope is that using protein C testing for patients
taking Xigris will improve the benefit-risk profile for the medication,
which can cause bleeding.
The PROWESS study leading to FDA approval of the drug
showed that the medication significantly reduced mortality for people
with severe sepsis. But a followup clinical trial, the ADDRESS study,
investigating the use of Xigris in patients with less severe sepsis, was
not favorable, Dr. Williams says. It showed that Xigris failed to benefit
the lower-risk group of patients and that the incidence of bleeding was
almost identical to that seen in the PROWESS study.
Responding to a request for more data on Xigris from
the European equivalent of the FDA, Lilly has a global study scheduled
to start in March 2008 called PROWESS-SHOCK. That trial will involve about
1,500 patients over about two years to see if Xigris reduces mortality
in septic shock, Dr. Williams says. The primary end point is 28-day mortality
from all causes, which is the classic end point for a sepsis trial.
Thanks to animal model studies, Lilly now has a better
grasp on Xigris' mechanism of action than it had in the initial PROWESS
trial. "We know that Xigris has an anticoagulant effect, but now we believe
that the drug's main effect is as an anti-inflammatory agent," Dr. Williams
says. The drug may reduce inflammation "by binding to white blood cells
and decreasing their rolling and adhesion to the endothelium and through
specific receptor signaling pathways."
The University of Alabama's Dr. Abraham says that because
Xigris appears to have multiple mechanisms of action, the Xigris trials
may help physicians and scientists better understand the underlying pathology
Work continues on identifying sepsis biomarkers that
signal impending organ dysfunction in time to stave it off.
One emerging biomarker in the early stages of development,
the protein neutrophil gelatinase-associated lipocalin, or NGAL, shows
promise for detecting acute renal failure associated with sepsis perhaps
in time to turn it around, says Prasad Devarajan, MD. He is the Louise
M. Williams Endowed Chair and professor of pediatrics and director of
nephrology and hypertension at Cincinnati Children's Hospital Medical
"In sepsis, it isn't usually the bug that kills
you—it's the body's response to the bug that creates both pro- and
anti-inflammatory responses that ultimately kills the person," says Dr.
Devarajan. And part of that response is development of acute renal failure.
"If you take all the causes of acute renal failure,
sepsis leads the list as the No. 1 cause," he says. Of the 800,000 people
who develop sepsis in the U.S. annually, about half develop acute renal
failure. And 25 percent of those require dialysis, a group that has a
mortality rate exceeding 80 percent.
Yet a timely diagnosis of acute renal failure in sepsis
is hard to make, just as it is for other forms of acute renal failure,
because by the time physicians use the "gold standard—an increase
in creatinine—it's far too late to intervene," Dr. Devarajan says.
"We have published our first study showing that
in patients who have sepsis, urine NGAL can predict ARF one to two days
before creatinine goes up. We have a paper in revision now showing that
plasma NGAL does the same thing."
What might you do differently for a patient if you
knew he or she had elevated NGAL with sepsis? "That's the patient you'd
want to monitor very carefully in the ICU rather than putting him on a
regular floor," Dr. Devarajan says. "You'd have to be very careful about
maintaining the patient's kidney perfusion and avoiding nephrotoxic agents,
such as IV contrast for imaging or certain antibiotics. You need to be
informed to do no further harm."
Even in patients who do not develop full-blown acute
renal failure, he continues, a large volume of literature suggests physicians
should intervene with renal replacement therapy, such as hemofiltration
techniques that remove endotoxins and cytokines and related products in
the blood that add to the systemic disease.
In addition, he says, experimental therapies for acute
renal failure have been shown to work "beautifully" in animal models.
Yet researchers have spent millions trying the agents in humans without
success. "We think the reason they may not work is that they are administered
far too late—after creatinine goes up," Dr. Devarajan says. Having
an early biomarker for acute renal failure, such as NGAL, allows researchers
to redesign the studies and test a long list of 20 to 30 medicinal treatments
earlier to see if they improve outcomes.
The majority of studies on NGAL thus far, however,
have been single center studies that have been reasonably well done, but
they're small studies nevertheless, Dr. Devarajan cautions. So more work
needs to be done.
The University of Toronto's Dr. Klein observes that
NGAL seems to have a role as an early marker of renal dysfunction. And
"hopefully in the future, that can be tied to therapies to prevent or
treat early renal dysfunction potentially in sepsis."
The more that unique populations of sepsis patients
can be identified to target with specific, directed therapies, the better.
In doing so, Dr. Klein says, "perhaps we can undo the failures of the
last 20 years where billions have been spent on sepsis therapies that
have failed, probably in part because they were applied in too wide of
a clinical context so the wrong patients received them."
Karen Lusky is a writer in Brentwood, Tenn.