Culturing vaginal/cervical specimens
Q What are
the guidelines about what organisms to work up from routine cultures
from vaginal/cervical swabs?
A Vaginal infections (vaginitis/vaginosis)
are caused by a limited number of infectious organisms; namely
Trichomonas vaginalis and Candida spp. Bacterial vaginosis is known to
be caused by a synergistic interaction between multiple bacterial
species, both aerobic and anaerobic1 but is not diagnosed by bacterial
culture. Group A Streptococcus vulvovaginitis is a symptomatic but
benign infection of children (not adults).2 The role of Group
B streptococci (GBS) as an etiologic agent of vaginitis in adults has
not been established; it is considered a normal inhabitant of the adult
vaginal flora and is not associated with an inflammatory response.2
Staphylococcus aureus, the enterococci, and enteric Gram-negative
bacilli are also considered part of normal or contaminating flora and
have not been associated with adult vaginitis/vaginosis.
—Susan E. Sharp,
PhD, D(ABMM)
Director of Microbiology
Kaiser Permanente Pathology
Regional Laboratory
Portland, OR
References
- Winn WC, Allen S, Janda W, Koneman E, Procop G, et al. Infections of
the Genital Tract. In:
Koneman's color atlas and textbook of diagnostic microbiology.
6th ed. 2006. Philadelphia, PA: Lippincott Williams & Wilkins.
2006:88-89. - McCormack WM. Vulvovaginitis and Cervicitis. In: Principles and
Practice of Infectious Diseases. 6th ed. New York: Churchill
Livingstone. 2005:1357-1372.
CSF cell count on clear fluid
Q Our
emergency department insists we use tube #1 and tube #4 for
cerebrospinal fluid (CSF) cell count, even if the CSF is colorless.
The ER physicians say they want to differentiate subarachnoid
hemorrhage from traumatic taps. In the case of concurrent traumatic taps and recent subarachnoid hemorrhage, what we should
do?
A Most cases of
subarachnoid hemorrhage are diagnosed by computed tomographic (CT)
scanning of the brain. When the CT result is negative, however, most
physicians recommend a lumbar puncture to examine CSF. There are several
parameters measurable by obtaining a lumbar puncture that can aid in
diagnosis of a subarachnoid hemorrhage. These include elevated opening
pressure of the lumbar puncture, the presence of red blood cells (RBCs)
in the CSF, and the presence of xanthochromia in CSF.1 A
traumatic tap, however, can complicate the interpretation of the CSF
findings since it has features overlapping with those of a subarachnoid
hemorrhage. Since traumatic lumbar punctures are fairly common with an
estimated incidence of about 10% to 20%,2 the clinical
laboratory routinely needs to try to differentiate a subarachnoid
hemorrhage from a traumatic tap.
There is no specific threshold for the
number of RBCs in the CSF used to diagnose subarachnoid
hemorrhage or to differentiate subarachnoid hemorrhage from
traumatic tap. Subarachnoid hemorrhage has been reported with
“only a couple of hundred erythrocytes” in the CSF. CSF with a
RBC concentration of greater than 6,000 has been described as
grossly bloody, whereas a cell count from 500 to 6,000 yields
cloudy CSF. CSF with an RBC concentration of less than 400 to
500 appears colorless.3 For these reasons, a
colorless tube does not entirely rule out a subarachnoid
hemorrhage.
In order to distinguish a traumatic tap
from a true subarachnoid hemorrhage using the number of RBCs in
the CSF, the trend has been to perform a RBC count on both the
first and last CSF tubes collected (tube #1 and tube #4). CSF
samples from a traumatic tap generally show clearing of RBCs
with successive tubes, whereas those from a true hemorrhage show
a more stable RBC count. When the RBC count decreases to zero or
close to zero in tube #4, this is strong evidence for a
traumatic tap. Sometimes, the specimen shows incomplete clearing
in tube #4, however, representing a likely traumatic tap that
may or may not be superimposed on a subarachnoid hemorrhage.
In the case where there is suspicion of
both a traumatic tap and a subarachnoid hemorrhage, other CSF
parameters can help discern whether a subarachnoid hemorrhage is
present, such as the opening pressure, which is elevated in many
cases of subarachnoid hemorrhage but not in traumatic tap.
Furthermore, presence of xanthochromia, microscopic evidence of
erythrophagocytosis, and hemosiderin-laden macrophages are
findings indicating subarachnoid hemorrhage, as long as there
has not been a prior traumatic tap. Xanthochromia is
yellow-tinged supernatant of CSF, which results from a breakdown
hemoglobin that follows a hemorrhage. Three hemoglobin breakdown
products include oxyhemoglobin, bilirubin, and methemoglobin.
Oxyhemoglobin (with absorption at 416 nm, 540 nm, and 578 nm)
appears in CSF within two hours of onset of subarachnoid
hemorrhage and peaks within 24 hours to 36 hours. Bilirubin
(with an absorption curve between 400 nm to 500 nm) appears
approximately 10 hours after onset of bleeding. Methemoglobin
(with absorption at 540 nm, 575 nm, and 630 nm) can appear at
any time after oxyhemoglobin but is only seen with encapsulated
CNS bleeding.4 Xanthochromia can be accurately
measured by spectrophotometer based on the specific absorption
pattern.5
Because RBC lysis begins as early as one
to two hours after a traumatic tap, the CSF must be evaluated as
soon as possible to avoid false-positives. There is also a latex
agglutination immunoassay for cross-linked fibrin derivative
D-dimer, which is specific for fibrin degradation and is
negative in traumatic tap.6 False-positive results,
however, are sometimes seen in cases with DIC, fibrinolysis, and
trauma from repeated lumbar punctures.
Occasionally, a clinician may repeat the lumbar puncture at the
next higher vertebral interspace in an attempt to eliminate
confounding data from a traumatic tap.
Perform the RBC differential counts in
tube #1 and tube #4, even when blood is not visible in the CSF,
in order to help rule out a subarachnoid hemorrhage and/or a
traumatic tap. In cases where the differential is equivocal,
other CSF parameters may aid in the diagnosis.
—Karen MacDonell, MD
—Guang Fan, MD, PhD
Department of Pathology
Oregon Health and Science University
Portland, OR
References
- Shah KH, Edlow JA. Distinguishing
traumatic lumbar puncture from true subarachnoid hemorrhage.
J Emerg Med. 2002;23(1):67-74. - Shah KH, et al., Incidence of
traumatic lumbar puncture.
Acad Emerg Med. 2003;10(2):151-154. - Wallach J ed. Interpretation
of diagnostic tests. 7th ed. Baltimore, MD: Lippincott
Williams & Wilkins, 2000; 263-292. - Graves P, Sidman R. Xanthochromia
is not pathognomonic for subarachnoid hemorrhage.
Acad Emerg Med. 2004;11(2):131-135. - Edlow JA, Bruner KS, Horowitz GL.
Xanthochromia.Arch Pathol Lab Med.
2002;126(4):413-415. - Smith GP, Kjedsberg CR.
Cerebrospinal, synovial and serous body fluids. In: Henry
JB, ed.
Clinical Diagnosis and Management by Laboratory Methods.
20th ed. Philadelphia, PA: Saunders. 2001:403-411.
Propoxyphene in urine
Q Will any other drug
cause a positive propoxyphene result in a urine drug-screen test?
A
Propoxyphene (Darvon) is a synthetic narcotic, similar in structure to
methadone. It has a similar analgesic effect as other morphine-like
opioids. It is less potent than codeine and is sometimes prescribed in
combination with aspirin or acetaminophen. The drug is metabolized by
the liver and most of it is excreted in the urine as N-norpropoxyphene.
Because of its structural similarity to
methadone, some screening tests will cross react. For instance,
in the Roche Integra microparticle screening test, 0.9 gm/mL of
methadone will give the same reaction as 300 ng/mL of
propoxyphene. Other drugs were found not to crossreact.1
In gas chromatography-mass spectrometry, or GC-MS, confirmatory
tests, propoxyphene is distinct. Although it has the same
retention time as methadone, it has a different ionic pattern.
Propoxyphene is not commonly seen as an
abused drug, and most people using it have prescriptions for it.2
—edited by Brad
S. Karon, MD, PhD
on behalf of Daniel M. Baer, MD
References
- Cobas Integra 400/700/800,
Propoxyphene Data Sheet, 2004-2005. - Shults TF. Medical Review
Officer Handbook, 7th ed. Research Triangle Park, NC,
Quadrangle Research, LLC, 1999.
MLO's “Tips from the Clinical Experts” provides practical, up-to-date solutions to readers' technical and clinical issues from a panel of experts in various fi elds. Readers may send questions to Brad S. Karon, MD, PhD, by e-mail at [email protected].
Brad S. Karon, MD, PhD, is assistant professor of laboratory medicine and pathology, and director of the Hospital Clinical Laboratories, point-of-care testing, and phlebotomy services at Mayo Clinic in Rochester, MN.
Published: May, 2010
