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Screening: New and existing blood tests and blood markers

Men's Health, Age related illnesses, General, Women's Health | February 25, 2015 | Author: The Super Pharmacist

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Screening: New and existing blood tests and blood markers

If someone wants a general check-up, which tests are most relevant? You do not need to be a science-fiction fan to look forward to the day in which a physician can scan you with the handheld device and diagnose your illnesses. Medical science has certainly not progressed to that point, but with new diagnostics, we are getting closer.

Screening Blood Tests of Today

When you go to your physician, he or she will likely order a number of screening tests that have become routine practice. These will likely include electrolyte panel to measure things like sodium and potassium in your blood, check your blood glucose, and estimate kidney function. You will probably have a complete blood count, which measures red blood cells, white blood cells, and platelet levels. Your physician will also test your thyroid function and liver function from time to time. These tests ordered almost reflexively and performed on everyone. Results on these tests may be abnormal, but do not cause symptoms right away. Any changes on these tests may indicate mild or even severe disease.

Focused Testing and Screening

Focused Testing and ScreeningSome patients may need more focused blood tests or the results of the blood test may prompt further diagnostic studies. For example, a person with high creatinine levels, routinely measured with other electrolytes, may prompt the doctor to order more advanced studies in the kidney. On the other hand, when the patient reaches a certain age, they may require different screening tests, such as prostate specific antigen for men or mammograms for women.

This is the way medicine uses diagnostic blood tests—use rapid, inexpensive blood tests to screen everyone for common diseases; use some screening tests on people with higher risk or of certain ages; and if abnormalities exist on any of these screening tests, explore them further. 

Why Not Test Me for Everything Right Now?

A form of concierge medicine that has popped up recently seeks to tap into people's desire to know everything about their health as soon as possible. The most notable examples are things like whole body scans and full-length genome sequencing.

Whole Body or Wellness Scans

In a whole body scan, patients undergo a CT scan or MRI of their entire body, Then a radiologist looks for anything that appears abnormal. The radiologist may find increased calcium in the coronary arteries indicating atherosclerosis, aneurysms in blood vessels, or abnormal growths that may or may not be cancerous. These tests are not covered by any form of subsidy and can be expensive. They are not covered by insurance because physicians don't always know what to do with the information or the information that comes from the scans does not change clinical management. For instance, many of us have cysts or growths on the kidney that will never turn into cancer and never cause any problems. However, if the whole body scan shows this growth, the patient may insist that it be biopsied to make sure that it is not cancer. Therefore, the patient undergoes a needless surgical procedure, placing themselves at increased risk for something that would never be a problem. If a person has calcium plaques in their coronary arteries, what can be done? The same thing that is probably being done right now: cholesterol and blood pressure control, exercise, a healthy diet, smoking cessation, etc.

Personalised full-length genome sequencing

The same problems exist for genome sequencing. Even though we only finished mapping the human genome at the end of the 1990s, today you can have your entire genome sequenced for a few thousand dollars. You may think that this would allow you to know your genetic risk for all diseases, but this is not the case.

While we can sequence the entire genome for an individual person rather inexpensively, we are still years or decades away from knowing the significance of mutations or abnormalities in most genes. In fact, we only know the genetic basis for a small fraction of human diseases. So, while it is a novelty to have a copy of your own genome, the medical usefulness of it right now is very limited. Our understanding of the genetic basis of disease is growing rapidly.

It is safe to predict that within the next few decades, sequencing a person’s entire genome will no longer be a novelty, but will be a medical recommendation and commonplace. In the meantime, physicians must balance a patient's desire to predict the future of their own health with what is known about the disease.

Screening Blood Tests of the Possible Future

Some blood tests can help predict disease, but are not yet routine. These may or may not be available through your physician. Likewise, depending on your personal circumstances you may or may not benefit from these tests. Consult your physician.

Lp-PLA2

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a marker of blood vessel inflammation.1 Abnormally high levels of this substance in the blood indicates cardiovascular disease risk that may not be identified through traditional blood pressure and cholesterol measurements. While Lp-PLA2 testing may not yet be routine, it may be important for people who have family members who died of sudden heart attack early in life with no known cause.

Circulating microRNAs in cancer detection

Circulating microRNAs are small, stable bits of ribonucleic acids that can be detected in the blood. The microRNAs may be helpful in the detection of certain cancers, such as prostate cancer, earlier than other tests.2

Ovarian cancer biomarkers

Ovarian cancer is very difficult to detect and often becomes clinically apparent after the cancer has progressed. Therefore, it is quite important to find blood tests that will detect ovarian cancer in its earliest stages. For biomarkers, especially the first two, with the names MUC16, WFDC2, MSLN, and MMP7 show great promise as early indicators of ovarian cancer.3

Depression biomarkers

Researchers have discovered that the levels of nine different kinds of RNA that can be measured in the blood can accurately diagnose major depressive disorder in adults.4 Impressively, the levels of these RNA transcripts actually improve with cognitive behavioral therapy, the mainstay of neurological counselling therapy.

Alzheimer's disease biomarkers

Unfortunately, there is no definitive diagnostic test for Alzheimer's disease. Most studies focus on differentiating people with Alzheimer's disease from healthy individuals.

Alzheimer's disease biomarkersFor example, a recent study identified 11 blood markers increase while seven biomarkers decrease in people with the disease.5 It is unclear how early these changes occur in the disease and, consequently, their power to predict Alzheimer's disease in its earliest stages. Other research, and its earliest stages, provides a tantalising look at the future of Alzheimer's disease diagnosis. Researchers report that tests of insulin resistance in the brain, reflected in blood tests, may predict Alzheimer's disease up to 10 years before people experience symptoms.6

Down syndrome

During pregnancy, small bits of fetal DNA enter the mother's bloodstream. New, sensitive testing can determine which DNA came from the fetus and which came from the mother. The power of this differentiation is that a test can be performed in as early as 10 weeks gestation that can determine whether the fetus has trisomy 21, the genetic abnormality that causes Down syndrome.7

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References

1. Davidson MH, Corson MA, Alberts MJ, et al. Consensus panel recommendation for incorporating lipoprotein-associated phospholipase A2 testing into cardiovascular disease risk assessment guidelines. Am J Cardiol. Jun 16 2008;101(12A):51F-57F. doi:10.1016/j.amjcard.2008.04.019

2. Mitchell PS, Parkin RK, Kroh EM, et al. Circulating microRNAs as stable blood-based markers for cancer detection. Proc Natl Acad Sci U S A. Jul 29 2008;105(30):10513-10518. doi:10.1073/pnas.0804549105

3. Palmer C, Duan X, Hawley S, et al. Systematic evaluation of candidate blood markers for detecting ovarian cancer. PLoS One. 2008;3(7):e2633. doi:10.1371/journal.pone.0002633

4. Redei EE, Andrus BM, Kwasny MJ, et al. Blood transcriptomic biomarkers in adult primary care patients with major depressive disorder undergoing cognitive behavioral therapy. Transl Psychiatry. 2014;4:e442. doi:10.1038/tp.2014.66

5. Doecke JD, Laws SM, Faux NG, et al. Blood-based protein biomarkers for diagnosis of Alzheimer disease. Arch Neurol. Oct 2012;69(10):1318-1325. doi:10.1001/archneurol.2012.1282

6. Kapogiannis D, Boxer A, Schwartz JB, et al. Dysfunctionally phosphorylated type 1 insulin receptor substrate in neural-derived blood exosomes of preclinical Alzheimer’s disease. The FASEB Journal. October 23, 2014 2014. doi:10.1096/fj.14-262048

7. Twiss P, Hill M, Daley R, Chitty LS. Non-invasive prenatal testing for Down syndrome. Semin Fetal Neonatal Med. Feb 2014;19(1):9-14. doi:10.1016/j.siny.2013.10.003

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