Rhophylac and Positive Antibody Screen
Sunday, March 21, 2010

Rhophylac® is a sterile solution of anti-D, also known as Rho(D) Immune Globulin, which prevents immunization of Rh-negative women to the D antigen and hemolytic disease of the newborn. Rhophylac® is a high purity product that can be administered either intravenously (IV) or intramuscularly (IM).

Rhophylac is routinely given to all pregnant Rh negative women, who have not already developed anti-D, at 28 to 30 weeks of gestation. Since switching to Rhophylac approximately one year ago, the laboratory has noted several instances where a positive antibody screen at 28 weeks was later determined to have been caused by Rhophylac injection immediately prior to drawing a blood specimen for the antibody screeen. Rhophylac appears to be much more quickly absorbed into the circulation than older IM formulations of Rho(D) Immune Globulin. Therefore, it is much more likely to be detected in the antibody screen. Much time and effort have been spent trying to determine if anti-D was actively or passively acquired. Misinterpretation of these results could potentially result in failure to give RhIg postpartum. For these reasons, the 28-week blood sample should always be drawn prior to administration of Rhophylac.

posted by Fred Plapp @ 5:21 PM, , links to this post


Vitamin D Insufficiency in Kansas City
Sunday, February 21, 2010

A decade ago, physicians ordered vitamin D levels to assess bone health. Recent epidemiological studies have suggested that vitamin D deficiency may play an important role in the pathogenesis of cardiovascular disease, diabetes, cancer, multiple sclerosis, rheumatoid arthritis, asthma, periodontal disease and depression. Accordingly, demand for 25(OH) vitamin D testing has skyrocketed.

A hospital laboratory in Kansas City, MO, received orders for 1710 vitamin D levels in 2007, 11,331 in 2008 and 26,024 in 2009. Recently the results of the vitamin D measurements performed on adult Kansas City residents in 2009 were reviewed.
Reference range was 25-80 ng/mL. However, most experts believe that the optimal concentration of 25(OH) vitamin D is at least 30 ng/mL because this is the threshold for elevation of parathyroid hormone. Twenty five percent of Kansas Citians had Vitamin D levels below 25 ng/mL and 39% had levels below 30 ng/mL. Less than 1% of people had levels above the upper limit of the normal range. The prevalence of Vitamin D insufficiency in Kansas City falls within the 25 to 75% range reported by the Third National Health and Nutrition Examination Survey (Bone 2002;30:771-7).

The cost of performing vitamin D testing in 2009 exceeded $550,000. Given the high incidence of vitamin D insufficiency and the low risk of adverse effects from vitamin D supplementation, a more practical clinical strategy might be to simply recommend vitamin D supplementation without ordering testing.

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posted by Fred Plapp @ 3:55 PM, , links to this post


Measuring Lipids after an Acute Coronary Syndrome
Sunday, February 07, 2010

The MIRACL (Myocardial Ischemia Reduction with Acute Cholesterol Lowering) trial demonstrated that early intervention with statins reduces the subsequent cardiac event rate. Other evidence has indicated that if hospitalized patients do not receive statins during their hospital stay, they are less likely to ever start taking these medications. Nationwide, less than 50% of patients have serum lipids measured within 24 hours of admission. One reason that physicians may not order lipid testing early after an acute coronary syndrome (ACS) is the long held belief that lipid measurements are unreliable during an acute event.

Recently, researchers from the University of Michigan analyzed data from the LUNAR (Limiting UNdertreatment of lipids in ACS with Rosuvastatin) trial to assess lipid changes 1 to 4 days after ACS onset (J Am Coll Cardiol 2008;51:1440-5). The goal of this prospective, multicenter, randomized, open-label, three arm study was to compare the efficacy of rouvastatin 20 mg and 40 mg with atorvastatin 80 mg in lowering LDL cholesterol over 6 to 12 weeks of once daily therapy. Of the 507 patients available for analysis, 212 were admitted for STEMI, 176 for non-STEMI and 119 for unstable angina.

Before treatment, serum lipids were measured on days 1, 2 and 4 after onset of ACS symptoms. LDL cholesterol levels decreased from an average of 136 to 134 mg/dL during the 24 hour period immediately following admission and then increased to an average of 142 mg/dL over the subsequent 2 days. Total cholesterol followed a similar trend. These changes were not considered to be clinically meaningful. HDL cholesterol and triglycerides exhibited minimal change during the 4 day period. The same trend was observed in the overall study population as well as in each of the three ACS subgroups.

Lipid Day 1 Day 2 Day 4
LDL-C 136 134 142
Total-C 200 197 208
HDL-C 39 39 40
Triglycerides 183 177 177

This study suggested that in-hospital lipid determinations are reliable and can form the basis for initiating lipid-lowering therapy.

posted by Fred Plapp @ 7:20 PM, , links to this post


PCR Triumphs in Clostridium difficile Toxin Detection
Sunday, January 10, 2010

Clostridium difficile is a Gram-positive, spore-forming, anaerobic bacillus that is associated with pseudomembranous colitis. The disease formerly known as C. difficile-associated disease (CDAD) is now called C. difficile infection (CDI). CDI ranges in severity from mild diarrhea to fulminant colitis. Risk factors for CDI include antibiotic use within three months prior to symptom onset and exposure to a health-care setting. Colonization with C. difficile is common in hospitalized patients (20-40%), while only 3% of healthy adults are colonized. CDC data indicates that the incidence and severity of CDI has been increasing since the year 2000. The recently described hypervirulent C. difficile strain has now been reported in 38 states, & presents a new challenge for infection control. Community-acquired infections, many without identifiable risk factors, are increasing as well.

Alterations of normal gut flora, resulting in overgrowth of C. difficile, are believed to initiate CDI. Production of exotoxins A & B by the organism subsequently results in colonic mucosal damage, and detection of these toxins is the basis for diagnostic laboratory tests. The majority of U.S. laboratories utilize enzyme immunoassay (EIA) for this purpose, due to rapid turn-around time & ease of use. However, the sensitivity & specificity of EIA is widely variable, as low as 50% and 70%, respectively. More accurate toxin detection is achieved by cell culture cytoxicity assays, however this technique requires 48 to 72 hours to obtain results. Conversely, there are recent favorable reports in the literature regarding the utility of real-time PCR for CDAD diagnosis. (Ann Intern Med. 2009;151;176-179, JCM 2009; 47; 3211-3217)

The PCR test performed in our laboratory targets the tcdA & tcdB genes that encode for toxin A & B. Parallel testing of 204 residual stool samples submitted for C. difficile toxin EIA was performed by PCR, with discordant samples submitted to a reference laboratory for further testing by PCR with different gene targets. There were 121 negative samples and 83 positive samples by EIA. Of these, 124 samples tested negative and 76 samples were positive by both PCR assays. Our laboratory’s PCR was positive in 4 samples, which were negative by both EIA & the reference laboratory PCR. The overall sensitivity and specificity of our PCR, compared to the reference PCR method, were 100% and 97% respectively.

The evaluation also included data from 18 patients with multiple inconsistent results by EIA. Based on the majority of results, 13 of these cases were judged to be true negative & 5 true positive. PCR evaluation of these specimens yielded consistent results in all cases. In 3 true positive cases, PCR detected toxin up to one day earlier than EIA.

Due to improved sensitivity & specificity of the PCR assay, only one stool specimen per patient should be submitted for testing. Specimens should be submitted fresh (refrigerated unless transported to the laboratory immediately) or in Cary-Blair transport media.

posted by Fred Plapp @ 8:18 PM, , links to this post


INR by ISTAT
Wednesday, December 09, 2009

Point of care testing on an ISTAT device has been available in the Emergency Department since February 2009. Recently, a member of the medical staff notified the laboratory about a significant discrepancy in INR results between the ISTAT and the laboratory; ISTAT INR was 1.5 and the laboratory value was 2.2. This call prompted a clinical pathologist to review 214 cases in which both ISTAT and lab INR results were available. In 198 cases (7%) both results agreed within 0.2. In 16 cases (7%) the parallel results differed by 0.3 or greater (range 0.3 - 3.0). These discrepancies occurred most commonly when the ISTAT INR was >1.5. There have only been 19 cases with an ISTAT INR >1.5, but 11 of the 19 (58%) differed by more than 0.3. In 7 of the 11 cases, the ISTAT result was higher and in the remaining 4 cases the ISTAT result was lower. This latter category is probably the most worrisome for determining which patients are candidates for TPA therapy.

The results became more discrepant the higher the INR. For example, a difference of 0.9 occurred on two occasions with an INR in the range of 1.7. In one case with an INR of 3.5, the INR differed by 2.1 and in one case with an INR of 4.9, the results differed by 3.1.

After reviewing this data, the laboratory has concluded that ISTAT INR does provide a rapid and reliable result if the INR is 1.4 or lower. However, all INR values of 1.5 or greater should be confirmed by a laboratory INR before any therapeutic decisions are made.

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posted by Fred Plapp @ 8:11 PM, , links to this post


HbA1c for Diagnosis of Diabetes
Wednesday, November 18, 2009

Hyperglycemia has been the sole diagnostic criterion for diabetes since the development of blood glucose assays more than 100 years ago. Despite being the gold standard, measurement of blood glucose is less accurate and precise than most physicians realize. Blood glucose measurements are also subject to several limitations including:

8-12 hour fasting specimen requirement
Diurnal variation requiring morning collection to capture peak levels
Large biological variation of 5-8%
Nonstandardized instrument methods with >12% bias compared to the reference method
Glycolysis after collection, even in sodium fluoride tubes, causing falsely decreased glucose levels

Traditionally, measurement of HbA1c levels has been largely restricted to monitoring diabetic patients. Very recently, HbA1c was endorsed for diagnosis of diabetes by an International Expert Committee (Diabetes Care 2009, 32 (7):1327-1334). A diagnostic cutpoint of 6.5% was recommended, based on the risk for developing microvascular complications such as retinopathy. Patients who have an HbA1c of 6.0 to 6.4% are considered at high risk for developing diabetes and cardiovascular disease in the future. These individuals should be identified and counseled about lifestyle modifications such as exercise and weight loss. An elevated HbA1c should be confirmed with a repeat measurement on a different day, except in those individuals who are symptomatic and also have plasma glucose over 200 mg/dL. HbA1c testing is indicated in children in whom diabetes is suspected but the classic symptoms and a casual glucose >200 mg/dL are not found. Analysis should be performed on central laboratory instruments and not with point of care devices, which have not been shown to be sufficiently accurate or precise for diagnosis.

The advantages to using HbA1c are:
Better index of overall glycemic exposure & risk of complications
Low intraindividual variability (<2%)
No requirement for fasting or timed specimen
Standardized methods with precision <2%
Less affected by acute illness or stress
Good stability after blood collection
Single test can be used for both diagnosis and monitoring

Some arguments against using HbA1c include the limited number of studies that have been performed thus far to derive the diagnostic cutoff and the increased expense of HbA1c compared to glucose.
A couple of issues appear somewhat confusing. First, the upper limit of normal for HbA1c is 6.0% and the diagnostic cutoff for diabetes is 6.5%, leaving a gray zone of values that are not normal but not high enough to qualify as overt diabetes. However, the risk for diabetes based on glycemia is a continuum and there is no single threshold at which risk clearly begins. The other apparent contradiction is that the diagnostic threshold for diabetes is defined as 6.5% while the recommended treatment target, which is based on glucose testing, remains at 7.0%. Additional clinical research will be needed to resolve these important issues.

posted by Fred Plapp @ 8:27 PM, , links to this post


Cocaine Has Become More Dangerous
Monday, October 26, 2009

Cocaine is often deliberately diluted with other substances at some stage of production, packaging or distribution to increase the apparent quantity (salt, sucrose, lactose, starch, or ascorbic acid), produce a complementary effect (procaine, benzocaine or tetracaine) or attentuate side effects (diltiazem or hydroxyzine). Recently, the Special Testing and Research Laboratory of the U.S. Drug Enforcement Administration has detected levamisole in more than 50% of Columbian cocaine shipments that have been intercepted. It is a veterinary deworming agent that can be purchased in bulk on the Internet. Levamisole may provide a complementary effect to cocaine by acting as a ganglion nicotinic acetylcholine receptor agonist.


The major adverse effect of levamisole is severe agranulocytosis, possibly by stimulating formation of IgG and IgM anti-neutrophil antibodies and anti-neutrophil cytoplasmic antibodies (ANCA). Physicians should consider the possibility of levamisole adulterated cocaine in patients who present with otherwise unexplained fever and agranulocytosis.


Levamisole is not detected by routine drugs of abuse screening and is difficult to detect by gas chromatography/mass spectrometry because the elimination half-life is only 5.6 hours and only 2-5% of the drug is excreted unchanged in urine.


posted by Fred Plapp @ 3:55 PM, , links to this post