Preimplantation Genetic Diagnosis and Screening

BlastocystPreimplantation genetic testing is a way of examining the genetic features of a developing embryo during the process of in vitro fertilization, before pregnancy. After the egg is fertilized with sperm, the embryos develop to the cleavage-stage. On day 3 after fertilization, a single blastomere is removed from the embryo for genetic evaluation using techniques such as PCR, FISH, or comparative genomic hybridization.

Preimplantation genetic diagnosis (PGD) is used to select embryos without certain genetic disorders. This testing including three major groups of disease: sex-linked disorders, single gene defects, and chromosomal disorders.

Preimplantation genetic screening (PGS), is not used to detect disease, but as a screen to select embryos for such things as: matching HLA type in order to be a tissue donor for an affected sibling, selecting gender, selecting embryos with the least predisposition for developing certain cancers, and selecting embryos with a higher chance of implantation and therefore increase the likelihood of achieving pregnancy. Medscape has an excellent overview of PGD and PGS.

For women of advanced maternal age or couples with known genetic mutations, the ability to screen for embryos free of certain genetic mutations is reassuring. However, as with many medical interventions associated with human reproduction, PGS has raised ethical questions. For instance, as stated earlier, PGS can be used to select for a preferred gender. In some cases this is to avoid a sex-specific disease. Other times this is done for so-called "family planning" or "gender balance." In other words, selecting a gender because of personal preference. Some feel this is discriminatory and should not be allowed. In other cases, embryos have been tested so that the resulting child would be compatible to serve as a stem cell donor for a sick sibling (much like the popular fiction book "My Sister's Keeper").   There have also been cases where parents have requested the selection of affected embryos so that the child has the same minor disability, such as deafness or dwarfism, as the parents. Some preimplantation genetics laboratories agree to do this type of testing and some do not.

The New York Times recently ran an article discussing this issue. The article states that:

"In the United States, there are no regulations that limit the method’s use. The Society for Assisted Reproductive Technology, whose members provide preimplantation diagnosis, says it is 'ethically justified' to prevent serious adult diseases for which 'no safe, effective interventions are available.' The method is 'ethically allowed' for conditions 'of lesser severity' or for which the gene increases risk but does not guarantee a disease."

The January issue of Clinical Chemistry published a Question and Answer piece entitled "The Ethical Implications of Preimplantation Genetic Diagnosis." A podcast interview with two of the authors is also available.

The paper summarized the opinions of an ethicist, an attorney, and the director of a preimplantation genetics laboratory. The ethicist indicated that in the past, PGD has focused mainly on reducing the risk of transmitting serious diseases. In the future, he sees a shift away from lifesaving interventions to more ‘eugenically’ inspired interventions. That is, looking for traits that parents do not want in their children and selecting for traits that they do want in an attempt to pass them on. The morality of eugenics is a key moral as this technology moves forward.

Indeed it will be interesting to see where the future of this technology lies. Although it is practiced routinely, the indications, utility, and outcomes of PGD and PGS are still being defined.

Examination of eleven hospital hCG devices for false negative results

Beckman Icon 20In previous blog posts we have discussed false negative urine hCG tests due to high concentrations of hCG beta core fragment (hCGβcf), the predominant form of hCG found in urine after six weeks of pregnancy. High concentrations of hCGβcf saturate either one or both of the antibodies used in the test. This hCG variant effect prevents the development of a positive signal and generates a negative result despite the presence of intact hCG in the urine sample being tested.

The original studies were performed by adding increasing concentrations of purified hCGβcf to a urine sample obtained from a pregnant woman. The problem with this approach is that the relative abundance of hCG, hCGβcf and other hCG variants in the urine that may affect device performance vary between women. A standardized method, using defined concentrations of hCG, is needed to evaluate the performance of currently available devices.

In a recent publication, we describe a screening method that can be easily used to examine the effect of hCGβcf and have used this method to test eleven POC hospital urine hCG devices.

First, a wide range of purified hCG and hCGβcf concentrations were combined to prepare 2 solutions:

  • Solution A: 500 pmol/L (171 IU/L) intact hCG with 0 pmol/L hCGβcf and
  • Solution B: 500 pmol/L intact hCG with 500,000 pmol/L hCGβcf

These solutions were tested on two hCG devices, the results of which helped to define a screening method:  

Each device is tested with the two solutions and the intensity of the test bands are compared. If Solution B shows a lighter test band than solution A, then the device is susceptible to false negatives with hCGβcf.

Using these two solutions we compared the performance of 11 hospital urine hCG devices

  • SP hCG Combo Rapid Test, Cardinal Health
  • OSOM hCG Combo Test, Genzyme Diagnostics
  • hCG Combo, Alere
  • ICON 20 hCG, Beckman Coulter
  • ICON 25 hCG, Beckman Coulter
  • Elite Plus hCG, Cen-Med
  • Clinitest hCG Pregnancy Test, Siemens
  • hCG Urine Test, McKesson
  • QuickVue+ One-Step hCG Combo Test, Quidel Corporation
  • QuPID One-Step Pregnancy Test, Stanbio Laboratory
  • Sure-Vue Serum/Urine hCG-Stat, Fisher HealthCare

Interestingly, we found that only 2 devices were acceptable (i.e. not affected by the hCG variant effect). These were the Beckman Icon 20 (shown above) and the Alere hCG Combo devices. By contrast, the Genzyme OSOM and Cen-Med Elite Plus hCG devices were the most susceptible to false negative results due to hCGβcf (OSOM shown below). The remaining seven were moderately affected.


The paper also demonstrated that devices that gave the strongest signal with hCGβcf alone were those that were least likely to show a false negative effect.

The screening method can be used by device users and manufacturers to evaluate hCG devices for inhibition by hCGβcf. We hope that the results of this study will help healthcare providers make informed decisions about which hCG devices to select, especially in medical centers that are unable to perform rapid, quantitative measurements of hCG in serum.

However, while the availability of hCG test devices that are not affected by hCGβcf is certainly reassuring, quantitative serum measurement of hCG should still be the test of choice when available.

Screening recommendations for gestational diabetes mellitus

Green check markThis blog has covered the topic of gestational diabetes mellitus several times. Recent big news in this arena is the recommendation from the U.S. Preventative Services Task Force (USPSTF) that all pregnant women be screened for gestational diabetes mellitus (GDM) after 24 weeks of gestation.

The USPSTF is an "independent panel of non-Federal experts in prevention and evidence-based medicine and is composed of primary care providers." Their job is to "conduct scientific evidence reviews of a broad range of clinical preventive health care services and develop recommendations for primary care clinicians and health systems." For the USPSTF to "recommend" a practice means that there is evidence to suggest that the benefits of that practice outweigh the harms.

First, a few facts about GDM:

  • Each year, about 4 million women give birth and about 240,000 of these women (6%) develop diabetes during their pregnancy. The actual number of women identified as having GDM depends on the screening test that is used.
  • Over the last 2 decades, GDM has become more common because more women are at risk of developing diabetes. Risk factors include being overweight or obese or having a family history of diabetes.
  • Even though GDM usually goes away after pregnancy ends, it still puts the mother and the fetus at risk of serious health issues. For the mother these include preeclampsia and an increased chance for the development of type 2 diabetes after pregnancy. For the fetus these include macrosomia (a high birth weight which makes delivery difficult and Cesarean section more likely), shoulder dystocia, and an increased risk of becoming obese during childhood.

The USPSTF recommended screening for GDM after 24 weeks of pregnancy in all women who do not already have symptoms of diabetes. They gave this recommendation a grade of "B," meaning that there is a high certainty that there is moderate certainty that the net benefit of GDM screening is moderate to substantial.

Women benefit from GDM screening because it:

  • Identifies those who have GDM and who should be treated (usually with diet modifications, glucose monitoring, and, if needed, insulin therapy).
  • Lowers the risk of preeclampsia, fetal macrosomia, and shoulder dystocia.

The harms of screening were minimal and included:

  • Anxiety in some women.
  • The use of unnecessary tests and services.

The Task Force did not find sufficient evidence to support screening for GDM before 24 weeks of pregnancy and gave that statement a grade of "I," meaning was insufficient evidence to assess the balance of the benefits and harms of GDM screening.

The USPSTF did not make any recommendations regarding what GDM screening test to use. As this blog has noted before, there is no universally accepted method for diagnosing GDM and this has resulted in 5 different approaches (and considerable debate).

The history of pregnancy tests

HCG croppedIf you are interested in hCG, like we are, you might be interested in a recent paper, in Clinical Chemistry, by Dr. Glenn Braunstein entitled "The long gestation of the modern home pregnancy test."

Dr. Braunstein is one of the researchers that helped develop the first radioimmunoassay specific for hCG in the 1970's and is a leader in the field of hCG.

In his paper, Dr. Braunstein reflects on the history of urine pregnancy tests.  He explains that there is actually a description of a pregnancy test in ancient Egyptian papyrus writings. In that test, women urinate on wheat and barley seeds. If neither grows the woman is not pregnant. If the barley grows it will be a male and if the wheat grows it will be a female!

The first bioassay was described in 1927 by the German scientists Ascheim and Zondek who demonstrated ovarian stimulation in mice when they were injected with the urine from pregnant women. After that, there were many bioassays developed to detect pregnancy. Apparently these had analytical sensitivities of between 100-18,000 IU/L and they took 2-9 days to get a result!

The first radioimmunoassay for hCG & LH (leuteinizing hormone) was described in 1966 by Midgley.  Its analytical sensitivity was very high by today’s standards (175 IU/L) but, of course, it recognized both hCG and LH and it took 3 days to perform. The similarity between hCG and LH was a real problem. It was not until Dr. Braunstein, together with Dr. Judith Vaitukaitis, developed new antibodies that were specific to the hCG beta subunit that an hCG-specific assay was developed. With this assay, they were able to detect pregnancy as early as 7.5 days after fertilization and they were able to develop reference intervals for serum during pregnancy.

The first home pregnancy test marketed in the U.S. was the e.p.t.® ("Early pregnancy test") in 1977. It was described as a "private little revolution" because it allowed women to determine if they were pregnant in the privacy of their own home with no one else knowing. Today, pregnancy tests account for $228 million dollars in annual sales and take up considerable shelf space at retail stores with different brands and styles (see photo).  

For further reading, another great reference for the history of the pregnancy test was created by the NIH library and can be found here.

A rapid pregnancy test without using urine? Not so fast.

The rapid assessment of pregnancy status is important in urgent health care settings. Determining if a Tube of blood woman is pregnant or not is necessary to:

  • Determine if symptoms such as abdominal pain, vaginal bleeding, and/or vomiting are due to pregnancy;
  • Prevent fetal exposure to sources of radiation (x-ray, CT, scan, etc);
  • Prevent the administration of teratogenic medication.

In many health care setting, qualitative urine hCG testing is often used to quickly determine a woman's pregnancy status. Several posts on this blog have discussed the limitations of this type of testing (see here and here for some background). We have often advocated for the use of quantitative serum hCG testing over qualitative urine testing for this purpose but there are some logistical challenges with quantitative serum testing:

  • The use of a blood sample requires its collection and transport to a central laboratory.
  • Once received in the lab, a blood sample has to be centrifuged to separate the serum (the liquid part of the blood that is actually tested) from the blood cells.
  • Both of the above steps increase the amount of time needed to perform the test and report the result to the physician.

Although many qualitative hCG tests used in health care settings can be used with either urine or serum, qualitative serum testing is impossible to perform at the point-of-care. This is because obtaining serum requires centrifugation of the whole blood and centrifugation can't practically be done outside of a laboratory.

Recognizing that hCG tests performed on blood samples are generally better than thosed performed on urine, physicians are sometimes tempted to use whole blood (instead of serum) as the sample type for qualitative hCG testing at the point-of-care. An example of this type of use is described here.

That report describes the use of whole blood instead of urine or serum for the qualitative detection of hCG in a patient with a ruptured ectopic pregnancy. This was what I call a VBI: a Very Bad Idea. It is so wrong that two colleagues and I wrote to the journal that published the report to let them know it was a VBI.  Basically, we pointed out that:

  • Using whole blood instead of serum or urine was a modification of the intended use of an FDA-approved test and as such was against the law without appropriate validation experiments.
  • The peer-reviewers and journal editors failed to recognize that their report was in conflict with federal and state regulations and the report's publication essentially recommends the promotion of an unauthorized practice with serious patient safety risks.
  • Involving laboratory professionals to help identify solutions for clinical dilemmas involving laboratory tests is always a smart idea.

In response to our criticism, the authors replied with this:

"Physicians' judgment is relied upon to determine when benefit to the patient outweighs the risk of inaccuracy of unapproved use."

In other words they essentially said "we can do anything we want, regardless of regulations, when we act according to our best judgement."

How convenient. How utterly ignorant. How potentially dangerous.

Sadly, this type of mis-information is widespread. A website called "Emergency Physicians Monthly: The Indpendent Voice for Emergency Physicians" featured an article titled "Stat Pregnancy Test…Without Urine?" in September 2013. This article encourages the use of using whole blood for qualitative hCG testing and even provides a "Quick Trick" section on how to perform the test. This is grossly negligent on their part. I note that under the "Tips" section the author writes:

"Be sure to wait at least 5 minutes when using whole blood in the kit. It sometimes takes a while." (emphasis is mine)

Hmmmm, might someone want to define what "a while" is?

I think my opinion on this matter is evident. If reliable results are to be obtained and utilized for patient care decisions, clinical laboratory tests must be performed using validated methods (including the type of sample tested). To deviate from established protocols without guidance from laboratory professionals is a VBI.

    Pregnancy testing in the Emergency Department: a physician’s perspective

    Today's post is by a guest author, Ian Schwartz, M.D. Dr. Schwartz is an assistant professor of emergency medicine at the Yale University School of Medicine and the former medical director of the adult emergency department at the Yale-New Haven Hospital in New Haven, CT. Here, he provides his perspective on determining a patient’s pregnancy status in an emergency setting and describes the possible consequences of erroneous hCG test results.

    EmergencyThe practice of emergency medicine is a daily challenge for providers in the field. Patient histories are varied and nuanced and no two cases are ever the same.  In the hectic, chaotic and over-flowing hallways of the emergency department (ED), providers (not surprisingly) look to hang on to objective evidence in order to come up with diagnoses and treatment plans.

    Experienced providers realize, of course, that a diagnosis is usually a best guess. For the majority of patients, emergency room doctors are simply synthesizing a few facts and ideas into a coherent explanation for the symptoms that brought the patient to the ED.

    The challenge is that even those elements that we call facts are, themselves, nuanced. Every ED doctor has had the experience of staring at a chest x-ray and debating whether the patient had pneumonia or some fluid in their lungs. X-ray interpretation is literally dealing in shades of grey.

    As opposed to evaluating X-rays, laboratory test results would appear to be much more objective. The lab provides a discrete test result along with a reference interval for defining what is considered to be “normal.” For most health care providers the validity and accuracy of most test results go unquestioned. Yes, that patient absolutely has elevated calcium. Yes, this patient is anemic. Decisions for further testing, treatment and disposition are often made based solely on these test results.

    Emergency providers (and others who practice evidence-based medicine), think in terms of odds and probability. That is, they think about the likelihood of a disease. Some examples: the likelihood of a blood clot in the lungs given a patient’s risk factors or the 30-day likelihood of a heart attack if a patient with chest pain is sent home. Each ED doc has his or her own acceptable “miss rate” for a given condition.

    However, when it comes to pregnancy testing that sort of calculation and prediction simply doesn’t enter the mind of most ED providers. The pregnancy test is often considered to be the one single binary (yes/no) test that they can actually rely on.

    Most emergency departments perform qualitative hCG tests using a urine sample to determine a woman’s pregnancy status. The tests are similar to those that can be purchased over-the-counter and performed at home. The person performing the test will be handed the urine sample, perform the test, and (hopefully) chart that result into the medical record and (hopefully) alert a nurse or other care provider of the result.

    A provider sees this result and takes the appropriate action. There is usually no second thought about the quality of the test result. If it’s negative then the patient with abdominal pain is not pregnant and the physician can get the CT scan of the abdomen instead of the ultrasound. A negative result is also a license to order antibiotics, pain medications, and other drugs without concern for possible fetal harm. The urine hCG test is the standard way we define pregnancy in the emergency department and it gives the green (or red) light to treat the patient as not pregnant (or pregnant).

    There is a problem with this type of reliance: the urine hCG test, itself, is simply not good enough to tell us whether or not a patient is pregnant.

    Here are a few facts that most ED providers are unlikely to know about hCG testing:

    1. hCG appears in blood before urine, sometimes up to 5 days earlier.
    2. The claimed analytical sensitivity of most qualitative urine hCG tests is 25 IU/L whereas the quantitative blood assays are sensitive to 1-2 IU/L (commonly pregnancy is defined by greater than 5 IU/L).
    3. Even though common qualitative urine tests claim 99+% accuracy in determining pregnancy status, a recent study suggests that they are actually only 99% sensitive at an hCG concentration of 150-225 IU/L.
    4. There is a potential window of 3 to 7 days during the first trimester of pregnancy where a quantitative blood test will detect hCG while the qualitative urine test might not.
    5. Ectopic pregnancies can occur at hCG concentrations below what is detectable by current qualitative methods.
    6. In one study of over 11,700 urine samples, 69 (0.5%) of ED hCG test results were erroneous due to documentation errors, inherent deficiencies in qualitative tests or because the hCG concentration was below the level of detection.

    So what are some real-world consequences of not using the most accurate hCG test at our disposal? If we believe a patient with abdominal pain is not pregnant (when in fact they are) we order CT scans of the abdomen looking for appendicitis or other abdominal diseases. That CT scan just delivered 10 mSv of radiation to the mother and fetus and doubled the risk of the fetus developing a childhood cancer (1 in 1,000). Or we just ordered Motrin, a medication known to cause neural tube defects and a variety of heart defects. And we have just increased the risk of miscarriage two and a half fold.

    In a later post, I will address the erroneous belief that qualitative urine hCG tests are quicker to result than quantitative blood tests. However regardless of speed, ED’s across the country are utilizing a test that does not deliver the accuracy that most providers believe they are getting. This is a fact that should be quite troubling to all of us considering the number of urine pregnancy tests that performed each day. How many erroneous results are we are unknowingly receiving and what is the potential harm that is being done to a fetus in its most fragile period of growth?

    False Negative Pregnancy Tests Still a Real Problem in Home and Hospital Devices

    Neg pregnancy testWe have blogged in the past about false negative pregnancy tests due to hCG beta core fragment (hCGbcf).   After about 5 weeks of pregnancy (i.e. 3 weeks after the expected period) concentrations of hCGbcf, in urine, are higher than all other forms of hCG. Our group has shown previously that the concentration of hCGbcf can saturate one of the antibodies used in the point-of-care hospital pregnancy kits. As a result, test shows a negative result. The variant hook effect can be confirmed if testing shows a positive result after diluting the sample. This phenomenon is referred to as the "variant hook effect" and was reported to the FDA in 2009.

    Recently, our group took this observation one step further and examined over-the-counter home pregnancy devices to see if they were subject to the same problem.  We examined six over the counter devices and selected two that seemed to be most affected by the variant hook effect. We then compared those two devices to the hospital device that we had made our original observations in four years ago, and to a hospital device that we thought performs best when compared to various other hospital pregnancy devices. Not surprisingly, we found that the over-the-counter home pregnancy devices are also subject to the variant hook effect. However, what was a surprise was that the hospital pregnancy devices were more affected by hCG beta core fragment than the home pregnancy devices!  Furthermore, despite the fact that the variant hook effect was reported to the FDA in 2009, manufacturers have not changed their devices to avoid this problem. To hear more about this paper you can listen to a podcast describing the findings.

    Our laboratory is currently working to better define how much hCGbcf is required to cause the variant hook effect. We hope that this will help manufacturers to produce devices that avoid false negative results. In the meantime, several things need to be done:

    1. Physicians, nurses, and other health care professionals need to be educated about this problem-especially in the hospital setting.
    2. The variant hook effect should be made clearly visible in pregnancy test package inserts and they need to state that when a false negative is suspected, a simple dilution can yield a positive result if the patient is truly pregnant. This is very important for centers that have no alternative way of testing for pregnancy.
    3. Finally, in my opinion, quantitative serum hCG testing should be the preferred pregnancy test in centers where it is available. Serum testing is not subject to the variant hook effect because hCGbcf is not present in serum. Furthermore, quantitative serum assays are much more sensitive than the qualitative assays.

    Detecting hCG in urine: how low is low enough?

    A recent post on this blog described the inability of qualitative point-of-care (POC) hCG tests to detect hCG when it was present in urine or serum at a concentration that should, according to the test manufacturer, always be detected. The inability of these devices to detect hCG is a serious concern.

    A false-negative result from a home pregnancy test can be initially disappointing if a pregnancy is desired or a temporary relief if it is not. By contrast, a false-negative result in the health care setting can result in serious harm to the fetus if a patient who is assumed to not be preganant undergo interventions that are potentially harmul to the pregnancy.

    A recent case report has been published that, like other reports, emphasizes the limitations of qualitative urine hCG testing. The case describes a young woman who required radioactive iodine therapy for Grave's disease. Importantly, this young woman was also recently pregnant. That fact would likely not have been discovered had the physician relied on a qualitative urine hCG test. Fortunately, the laboratory had performed a quantiative urine hCG test (note that quantitative hCG tests using urine may be performed by the lab but the results are reported as qualitative (e.g. yes or no) and not the actual hCG concentration) which was interpreted as "positive" because the measured hCG concentration was greater than the lab's cutoff of less than or equal to 5 IU/L (it was 12 IU/L). A serum hCG test performed the same day produced a result 15 IU/L (not pregnant=less than or equal to 5 IU/L). Two days later a repeat serum hCG test produced a result of 147 IU/L confirming that she was in the very early stages of pregnancy. 

    As has been noted in this blog in the past (here and here), urine hCG testing is commonly performed in the health care setting because it is convenient. However, the problems with urine hCG tests are so numerous (see here and here) that urine hCG testing should not be relied upon to determine a patient's pregnancy status.

    The authors of the case described above correctly point out that the detection thresholds of most qualitative urine hCG tests are stated to be 20–50 IU/L (recent evidence suggest these cutoffs are not always accurate). Further, they call for more sensitive qualitative urine hCG tests in order to decrease the number of false-negative hCG results in the health care setting and suggest that a detection threshold of 5 IU/L (which is the same threshold used for interpreting quantitative serum hCG tests) should be used. Interestingly, this conclusion is similar to the one my group suggested in regards to qualitative serum hCG testing.

    I am in complete agreement that when it comes to the detection of early pregnancy, hCG tests that are capable of accurately detecting and/or measuring hCG are required. Currently, this means that serum hCG tests should be used exclusively, in the health care setting, for this purpose. To rely on less sensitive tests and less accurate urine hCG tests is a disservice to our patients.

    Wanted! A sensitive qualitative hCG test.

    Today’s post is by a guest author, Dina N. Greene, Ph.D. Dr. Greene is a Scientific Director at Northern California Kaiser Permanente Regional Laboratories in Berkeley, CA. She discovered that qualitative hCG tests may not be as analytically sensitive as we all have come to believe and she shares her observations here. A report of her work has been published in Clinica Chimica Acta.
    Neg pregnancy test
    The assessment of very early pregnancy (from conception until about two weeks following the
    expected menses) is dependent on the detection of hCG in serum or urine. In health care settings a urine sample is often the specimen of choice because it is convenient and usually easy to obtain.

    When urine samples are tested for hCG they are most frequently tested using qualitative (yes/no) point-of-care (POC) devices. This type of testing is attractive because it is performed close to the patient and the test results can be obtained within minutes. In general, when challenged with urine or serum containing hCG these devices work well. However, what was not known was how sensitive these devices are for detecting very early pregnancy. That is, could pregnancy be ruled out if a qualitative POC test was negative?

    To answer that question we completed a study that took a systematic approach to this question by testing urine and serum specimens collected from patients that spanned a wide range of hCG concentrations with two commonly used POC devices.

    While many concentrations of hCG were represented in these samples, we purposefully skewed the specimens so that a large percentage (~30%) had concentrations of hCG expected to be seen only in very early pregnancy. The results were surprising.

    We found was that the devices did not always detect hCG at the lowest detectable concentration claimed by the manufacturer (20 IU/L for urine and 10 IU/L for serum). In fact, we had many false-negative results when the urine concentration of hCG was as high as 200 IU/L or the serum hCG concentration was as high as 50 IU/L. We further showed that the urine specimens were collected from patients that were at approximately 4 weeks’ of gestation which, if calculated from the day of the last menstrual period, is close to the day of expected menses.

    Anecdotally, medical providers at some institutions have recognized this phenomenon. If a sexually active woman is unsure of her pregnancy status, and the POC urine hCG test result is negative, the provider may encourage the patient to return for retesting in a few days. Alternatively, if the patient’s pregnancy status must be known urgently, the provider may collect a blood sample for quantitative serum hCG testing performed in the laboratory to confirm the negative POC test result.

    Interestingly, the package insert of one qualitative hCG POC device used in our study states “If a negative result is obtained, but pregnancy is suspected, another sample should be collected and tested 48-72 hours following.” Most other hCG POC devices provide a similar disclaimer. Although it is empirically recognized that false-negative results are possible in early pregnancy, most individuals (health care professionals and consumers alike) assume that this corresponds to the period of gestation that precedes hCG production. What our study showed is that hCG is present in the urine and serum of these women, but the concentration is too low for the POC devices to always detect reliably.

    Discrepancy in Lamellar Body Counts (LBC) between the Sysmex XE-2100 and Sysmex XT-2000i instruments

    Recently, we blogged about a paper by Kyle & Lawrence that demonstrated poor precision of the lamellar body counts (LBC) using the Coulter Unicel DxH 800 instrument. Now we want to make you aware of a study by Beaudoin and others that demonstrates a bias in LBCs between the Sysmex XE-2100 and Sysmex XT-2000i instruments.

    Previous reports have demonstrated excellent concordance between the LBC when performed on Sysmex XE-2100 and the Coulter-brand instruments. However the Beaudoin  laboratory recently noticed a positive bias in LBC results using the Sysmex XT-2000i. Therefore, they conducted a study to compared LBC results in 52 specimens using two Sysmex models (Sysmex XE-2100 and Sysmex XT-2000i), with those of the Coulter LH-750.

    The authors demonstrated a very small negative bias (mean = -8%) between the Coulter LH-750 and the Sysmex XE-2100. However, the Sysmex XT-2000i had significantly higher results than the Coulter LH-750 (mean bias = 56%). Interestingly, despite the difference in LBCs, similar results were obtained on all 3 instruments when platelets were counted using Sysmex e-CheckTM control material or whole blood specimens.

    Using Deming regression to extrapolate the appropriate cutoff, the authors calculated that the medical decision limit for the Sysmex XT-2000i is closer to 77,000 counts/µL, which is 54% higher than the 50,000 counts/µL recommended for the Coulter LH-750. The reason for this difference is not understood, but is likely related to the different principles to count lamellar bodies on each instrument. Although, all three of the analyzers in this study use impedance principles to count platelets, each analyzer counts slightly differently. The authors speculate that the difference may be due to the fluid used for the hydrodynamic focusing of the samples.   

    This study once again highlights the need for manufacturer- as well as model-specific LBC clinical decision limits. Laboratories performing LBCs on hematology analyzers should be aware of this important analytical variable. Individual laboratory LBC cutoffs need to be established even when using the analyzers from the same manufacturer if the models are different.