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February 2014 Newsletter 
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Clinical Significance of Red Cell Antibodies
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Recent Blog Posts
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Clinical Significance of Red Cell Antibodies

 

When a physician orders a red blood cell transfusion, the blood bank performs compatibility testing which includes an ABO and Rh type and an antibody screen. The antibody screen detects alloantibodies and autoantibodies in patient plasma.  Approximately 95% of patients have a negative antibody screen which means that naturally occurring or expected anti-A and/or anti-B are the only red cell antibodies found in their plasma. If the antibody screen is negative, crossmatch compatible blood can be available within 15 minutes.

 

But what about those patients whose antibody screen is positive, indicating the presence of an unexpected red cell antibody? The answer is, it depends on the antibody detected. Red cell antibodies are notalike and are categorized according to their clinical significance. Some antibodies are capable of causing hemolytic transfusion reactions and/or hemolytic disease of the newborn and fetus while others are not. The table below categorizes the most common red cell antibodies by their clinical significance.

 

Significant

Insignificant

Duffy (Fya, Fyb)

A1

Kell (K,k)

Bg

Kidd (Jka, Jkb)

Chido/Rodgers

Rh (D, C, c, E, e)

Csa

Vel

HTLA

 

JMH

 

Kna

 

Lewis (Lea/Leb)

 

Lutheran(Lua/Lub)

 

M,N

 

McCa,Yka

 

P1

 

Sda

 

Xga

 

If an antibody is clinically significant, the transfusion service needs to provide red blood cells that are antigen negative for the corresponding antibody. For example, if a patient has anti-Kell antibody, they will be transfused with Kell negative blood. When a patient has multiple clinically significant antibodies(i.e. anti-K, anti-E, anti-Fya), the task of finding compatible blood becomes more challenging. Many times a large number of units must be antigen typed to find a single compatible unit of blood. This may necessitate sending the specimen to the consultation lab of our local blood center which maintains a larger inventory of red blood cells. The time required to find a sufficient number of compatible units can range from  hours to days depending on the complexity of the case.

 
If an emergent transfusion is required for a patient with one or more red cell antibodies, the transfusion service may not have time to supply compatible antigen-negative blood. In this situation, the risk to benefit ratio of transfusing incompatible blood to a patient with life threatening hemorrhage must be considered. Transfusion of incompatible blood is usually beneficial in these situations because most clinically significant antibodies do not destroy transfused red cells immediately. The transfusion service at Saint Luke's Hospital and the clinical pathologists are available on a 24x7 basis for consultation.

 

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Recent Blog Posts
02-24-2014 00:08:46 AM

Screening is a process of identifying apparently healthy people who may be at increased risk of a disease. The purported advantage of screening is to detect a disease at an early stage so that an individual can be offered information, additional tests and appropriate treatment to reduce their risk of complications or premature death. The FDA approved the use of PSA for early detection of prostate cancer in 1994. Since its introduction, PSA testing has dramatically changed the landscape of prostate cancer, creating a significant rise in cancer incidence and shifting the stage of disease at the time of diagnosis to a much earlier and potentially more curable stage. The 20 year risk of death from prostate cancer for a 55 year old man is 1.0% with screening and 1.3% without. Although prostate cancer mortality has declined approximately 30% during this time, many experts argue that this decline is more attributable to improvements in treatment than screening. Most recently, evidence has accumulated that any benefit of PSA screening is accompanied by a significant rate of overdetection and overtreatment of prostate cancer. Overdetection increases with age, rising from about 27% in men age 55 to about 56% at age 75. Most prostate cancers detected by screening with PSA are slow growing, not life threatening, and do not cause a man any harm during his lifetime. Unfortunately, there is currently no way to determine which cancers are likely to threaten a man's health and which will not. Consequently, more than 90% of men with PSA-detected prostate cancer decide to undergo treatment. New evidence from a randomized trial of treatment of prostate cancer detected by PSA screening indicated that approximately one third of men who underwent prostate biopsy experienced pain, fever, bleeding, infection, or transient urinary tract difficulties. Serious harms can also result from treatment. For every 1,000 men treated, 30 to 40 develop erectile dysfunction or urinary incontinence due to treatment, 2 have a serious cardiovascular event, and 1 dies of complications from surgical treatment (European Cancer Conference 2013, Abstract 1481). With this knowledge, several medical specialties have released updated guidelines in the past year. The United States Preventive Services Task Force (USPSTF) recommends that there is insufficient evidence to recommend PSA screening for anyone. The American College of Physicians (ACP) recommends that physicians inform men between the ages of 50 and 69 years about the limited potential benefits and substantial harms of screening for prostate cancer. ACP further recommends that physicians should NOT screen for prostate cancer using the PSA test in average-risk men under the age of 50 years, men over the age of 69 years, or men with a life expectancy of less than 10 to 15 years. The American Urological Association (AUA) guideline recommends that men between the ages of 55 to 69 years undergo shared decision making with their physician concerning the risks and benefits of PSA screening before undergoing PSA screening. AUA recommends against prostate cancer screening for men under age 40 years, men between the ages of 40 and 54 years at average risk and Men over the age 70 years or any man with less than a 10 to 15 year life expectancy. PSA should be used as an additional tool in the diagnosis and management of prostate cancer instead of a screening tool. It should no longer be used to screen for prostate cancer in asymptomatic men with average risk for prostate cancer....�

 

02-17-2014 01:33:23 AM

More than $100 million was spent by drug companies on advertisements for androgen replacement therapy (ART) in 2012. The ads appear to be successful because the number of prescriptions for ART among men 40 years or older has more than tripled since 2001 (JAMA Intern Med online June 3, 2013). Interestingly, among all new androgen users, only 74.7% had their testosterone level measured in the prior 12 months. The proportion of men with low testosterone could not be determined in this study. Common diagnoses in the year prior to testosterone replacement therapy included hypogonadism (50.6%), fatigue (34.5%), erectile dysfunction (31.9%) and psychosexual dysfunction (11.8%). Despite the claims touted in these ads, randomized clinical trials have shown that testosterone therapy results in only small improvements in lean body mass and body fat, libido, sexual satisfaction and has inconsistent or no effect on weight, depression, and lower extremity strength (J Clin Endocrinol Metab 2010;95(6):2536-59). Testosterone treatment has been associated with numerous adverse effects including polycythemia, gynecomastia, edema, prostate cancer, benign prostatic hyperplasia and coronary artery disease. Two articles published on February 3 in the New York Times further highlighted the cardiovascular risks associated with androgen replacement therapy in men (Don't ask your Doctor about Low T by John La Puma and Weighing Testosterone Benefits and Risk by Roni Caryn Rabin) Hopefully, coverage in the popular press will be more successful in decreasing this harmful practice than the medical profession has been. The Endocrine Society Clinical Practice Guideline does not recommend screening for androgen deficiency in the general population. The Guideline recommends making a diagnosis of androgen deficiency only in men with consistent symptoms and signs and unequivocally low serum testosterone levels. The initial test should be a total testosterone level measured on a sample collected during the morning. Low levels should be confirmed by repeat testing of total testosterone. Men who have total testosterone levels near the lower limit of normal or who may have a sex hormone binding globulin abnormality can be further investigated using bioavailable testosterone levels. Common practice has been to order both total and free testosterone in the evaluation of testosterone deficiency. To meet the growing demand, most laboratories measure free testosterone with an automated androgen analog immunoassay. Unfortunately, an increasing number of studies have demonstrated that these free testosterone assays do not accurately measure free testosterone and are often falsely low. The Endocrine Society recommends against the use of automated free testosterone assays (J Clin Endocrinol Metab 2010;95(6):2536-59)....�



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