Richard A. Savage, MD
pediatricians in our facility want us to perform a sweat chloride
test in our laboratory. Our test volume does not warrant including
such tests in our menu. What is the best alternative we can offer
our concerned pediatricians and obstetricians?
Your concern about adequate testing volume is valid. Not all laboratories
should perform sweat chloride testing to confirm the diagnosis of
cystic fibrosis. Laboratories need to perform a sufficient number
of sweat tests on a frequent basis to maintain competency. Points
to consider in meeting the needs of your local pediatricians and
- How close
is the nearest accredited CF care center? In many situations,
patients can be referred to a nearby accredited CF care center.
These centers are accredited by the Cystic Fibrosis Foundation
as having met criteria for sweat testing volume, methodology,
and quality assurance.
- Is a screening
test appropriate? The CF Foundation has approved the use of sweat
conductivity (Macroduct and Sweat-Chek, Wescor Inc., Logan, Utah)
as a screening test for community hospitals. A patient with a
sweat conductivity of 50 mmol/L or greater should be referred
to an accredited CF care center for a quantitative sweat chloride
test.1 When evaluating sweat conductivity results,
it should be noted that values from sweat conductivity methods
are approximately 15 mmol/L higher than sweat chloride concentrations.2
Laboratories performing screening tests need to provide the appropriate
reference intervals and must clearly inform physicians on the
report that the test is for screening, not diagnosis, and that
the test measures conductivity and not chloride.3
- Is the laboratory
providing in-house DNA testing or referral testing for CF carrier
status? The American College of Medical Genetics, American College
of Obstetricians and Gynecologists, and National Human Genome
Research Institute recommend that Caucasian couples be offered
preconception CF carrier screening using a pan-ethnic panel of
the 25 most common mutations. They also recommend that non-Caucasian
couples be informed of the availability of such screening.4
- CF Center
Directors Update No. 1. Bethesda, Md.: Cystic Fibrosis Foundation;
KB, Turcios NL, Gibson LE. Clinical evaluation of the Macroduct
sweat collection system and conductivity analyzer in the diagnosis
of cystic fibrosis. J Pediatr. 1994;124:255-260.
- LeGrys VA.
Common errors in sweat testing reporting for cystic fibrosis.
Lab Med. 2001;33:55-57.
- Grody WW,
Cutting GR, Klinger KW, et al. Laboratory standards and guidelines
for population-based cystic fibrosis carrier screening. Genet
A. LeGrys, DrA
Professor, School of Medicine
Division of Clinical Laboratory Science
University of North Carolina at Chapel Hill
Consultant, CAP Chemistry Resource Committee
Before initiating thrombolytic therapy or heparin therapy, our protocols
require preprocedure coagulation laboratory testing, which includes
activated partial thromboplastin time and prothrombin time. However,
therapy is initiated before our laboratory issues the results. How
reasonable is this practice? If an abnormal result is obtained or
if the specimen is unsatisfactory, it is no longer possible to recollect
after starting therapy.
is a balance between bleeding and thrombosis. Since bleeding is
a major side effect of thrombolytic therapy,1 the risk
of bleeding should be carefully assessed before starting thrombolytic
When urokinase was used for thrombolytic therapy in one study, researchers
found that 37 out of 82 patients had bleeding, with 22 patients
experiencing severe bleeding episodes.2 One contraindication
for thrombolytic therapy is known preexisting intracranial disease.
A separate study found there was a 1.9 percent risk of bleeding
among 312 patients who received thrombolysis for pulmonary embolism.3
Thrombolytic therapy should be approached with caution if a patient
has coagulopathy. A patient’s fibrinogen level typically should
be at least 100 mg/dL. If it is below this level, cryoprecipitate
is transfused to increase the fibrinogen to more than 100 mg/dL.
This is a reasonable approach since the fibrinogen level may decrease
after thrombolytic therapy due to fibrinogenolysis and may cause
bleeding. There are no guidelines or recommendations for acceptable
PT or partial thromboplastin time for thrombolytic therapy. A prolonged
PTT obviously does not mean the patient has a risk for bleeding
when it is associated with lupus anticoagulant or factor XII deficiency.
The presence of lupus anticoagulant is not uncommon for patients
who need thrombolytic therapy for pulmonary embolism since lupus
anticoagulant is one of the risk factors for thrombosis.
In conclusion, there are no standard recommendations regarding whether
PT and PTT should be checked before thrombolytic therapy. Though
definitive evidence is lacking regarding the utility of assessing
coagulopathy beforehand, I would recommend that PT, PTT, fibrinogen,
and complete blood count be evaluated before initiating thrombolytic
- Thabut G,
Thabut D, Myers RP, et al. Thrombolytic therapy of pulmonary embolism:
a meta-analysis. J Am Coll Cardiol. 2002;40:1660-1667.
SZ. Thrombolysis in pulmonary embolism: a debatable indication.
Thromb Haemost. 2001;86: 444-451.
- Kanter DS,
Mikkola KM, Patel SR, et al. Thrombolytic therapy for pulmonary
embolism. Frequency of intracranial hemorrhage and associated
risk factors. Chest. 1997;111:1241-1245.
Teruya, MD, DSc
Director of Blood Bank and Coagulation
Texas Children’s Hospital
Baylor College of Medicine, Houston
I need information regarding CAP or CLIA requirements for precalibrated
assays on automated instrumentation. The requirement for a calibrated
assay is usually to recalibrate at least every six months. Are precalibrated
assays from the manufacturer exempt from this requirement?
A. I assume by “precalibrated” that you mean an
FDA-cleared measurement system that does not use calibration materials that
simulate a patient specimen but instead has a process to identify the reagent
lot for a disposable unit use test module, which has encoded the calibration
settings. In this situation, the requirement is to follow the manufacturer’s
instructions. The manufacturer usually provides some type of control material
or process intended to verify the correct operation, including calibration,
of the measurement system. Additional guidelines can be found in NCCLS document
EP18-A, Quality Management for Unit-Use Testing; Approved Guideline (2002).
Greg Miller, PhD
Professor, Department of Pathology
Virginia Commonwealth University, Richmond
Consultant, CAP Chemistry Resource Committee