Screening Tests — Staying Healthy with Early Detection

Screening  2018

by Dr. Zach

 

  1. What is a screening test?  Pros and Cons.
  2. What screening tests are available?
  3. Cancer screening tests:
  1. Breast cancer
  2. Cervical cancer
  3. Colorectal cancer
  4. Lung cancer
  5. Prostate cancer

Talk to your doctor!

 

A screening test is done to detect health disorders or diseases in people who do not have any symptoms of disease.  In general, the earlier a disease is diagnosed, the better the chance of cure. Certain conditions increase one’s risk of other problems, such as high blood pressure, cholesterol, and diabetes,.increasing one’s risk of heart attack.  Diagnosing these conditions early allows us to control them, thereby decreasing the risk of heart attack and stroke.

 

Screening tests are available for many conditions, including cancers, cognitive impairment (early dementia), depression, diabetes, high blood pressure, impaired vision, and smoking.

The Canadian Task Force on Preventive Health Care (CTFPHC) was established by the Public Health Agency of Canada (PHAC) to develop clinical practice guidelines that support primary care providers in delivering preventive health care.  They use the research available to determine which screening tests are useful and which are not. The guidelines are regularly updated when new data becomes available.

 

Some of the most important screening tests are for cancer.  A good cancer screening test is one that is safe and that detects cancer early without many false positives (saying that cancer is there when it is not) or false negatives (saying that cancer is not there when it is).  False negatives are harmful because they falsely reassure, and false positives are harmful in that they lead to unnecessary anxiety and potentially to further unnecessary tests, which may incur risks of their own.

 

The task force has screening recommendations for the following cancers:   Breast (last update 2011, new update expected this year), cervical cancer (2013), colorectal cancer (2016), lung cancer (2016), and prostate cancer (2016).  It is important to note 2 things — first, there are multiple organizations that make recommendations about screening, including the US Preventive Services Task Force and individual cancer societies.  The CTFPHC is just one whose conclusions are evidence based. The second is that general recommendations apply to people at average risk. In general earlier screening is required for people at higher risk for cancer due to things like family history of lifestyle.

 

Brief summaries of the current recommendations are below.  For more information see https://canadiantaskforce.ca.

 

Breast Cancer:

 

The most recent CTFPHC recommendations state that for average  risk women routine screening is not recommended for women ages 40-49, either by mammography, breast self examination or clinical breast examination by a physician.  For women ages 50-74, screening by mammography is recommended every 2-3 years, but breast self-examination and clinical breast examination by a physician are not recommended.  No recommendation is made for women > 74 years of age because there is not enough data to make a general recommendation. This is a decision to be made in consultation with a physician.

 

For average risk women this group feels that the evidence suggests that there may be more harm from breast self-examination and clinical breast examination by a physician than benefit in saving lives.  As noted, the harm comes in the form of unnecessary anxiety and testing.

 

Ultimately the decision whether to perform a screening test is an individual one, to be made in consultation with your doctor.  A woman in her 40`s may well decide that the relatively small reduction in mortality associated with mammography is worth the risk of potential unnecessary worry and testing.  This is a decision she needs to make with her physician.

 

Cervical cancer:

 

Recommendations are presented for screening asymptomatic women who are or have been sexually active. They do not apply to women with symptoms of cervical cancer, previous abnormal screening results (until they have been cleared to resume normal screening), those who do not have a cervix (due to hysterectomy), or who are immunosuppressed.

For women 24 and younger they recommend no screening for cervical cancer.  The recommendation is for women aged 25-69 to be screened for cervical cancer (with Pap test) every 3 years.  Women aged 70 and older should continue being screened thusly until they have 3 negative tests in 10 years, at which time screening can cease.

 

Colorectal cancer:

 

These recommendations apply to adults aged ≥50 years who are not at high risk for colorectal cancer (CRC). They do not apply to those with previous CRC or polyps, inflammatory bowel disease, signs or symptoms of CRC, history of CRC in one or more first degree relatives, or adults with hereditary syndromes predisposing to CRC (e.g. familial adenomatous polyposis, Lynch Syndrome).

The recommendation is to to start screening for CRC at age 50 and continue until age 74.  Screening is done with one of 2 tests which detect microscopic amounts of blood in the stool — the FIT test, which stands for fecal immunochemical test, or the  gFOBT, the guiac-based fecal occult blood test. These are to be done every 2 years, or flexible sigmoidoscopy (looking in the sigmoid colon with a camera) every 10 years.

For people with 1st degree relatives with CRC, the recommendation is to begin colonoscopy at age 50 or 10 years earlier than the age of the first-degree relative was diagnosed with CRC, whichever occurs first, every 5 years.

Lung cancer:

These recommendations apply to adults aged 18 years and older who are not suspected of having lung cancer. These recommendations do not apply to individuals who have a history of lung cancer, or suspected lung cancer.

The recommendation is for adults aged 55-74 with at least a 30 pack-year smoking history (smoking a pack per day for 30 years) who still smoke or quit less than 15 years ago to have annual screening with low dose computed tomography (CT scan) annually up to three times.

 

Prostate Cancer:

This guideline applies to all men not previously diagnosed with prostate cancer. This includes men with lower urinary tract symptoms (nocturia, urgency, frequency and poor stream) or with benign prostatic hyperplasia (BPH).

The current recommendation from the CTFPHC is not to screen with the PSA (prostate specific antigen, a blood test) at any age.  They also don’t recommend that doctors perform a rectal examination, which has been used as another screening test for prostate cancer.  This is quite different from some other organizations. For example, the Canadian Urological Association recommends offering PSA screening to men as of the age of 50 (or age 45 for men at increased risk, such as those with a family history).  They state that the decision of whether or not to pursue PSA screening should be based on shared decision-making after the potential benefits and harms associated with screening have been discussed. For those who do get screened, the frequency of testing is to depend on the result of the previous test, with higher tests leading to more frequent screenings.  When to stop screening is also to depend on PSA level and life expectancy.

The CTFPHC does not recommend prostate cancer screening for the following reasons:

  • Only a small proportion of prostate cancer causes symptomatic disease or death whereas the majority is slowly progressive and not life threatening.
  • Screening with PSA may lead to a small reduction in prostate cancer mortality but does not reduce overall mortality.
  • No PSA value completely excludes prostate cancer
  • Harms (such as bleeding, infection, urinary incontinence, false positives and overdiagnosis) are common following PSA screening.

Screening tests are emotional and controversial.  Within my years of practice I have seen people who have been saved by screening tests not currently recommended by the CTFPHC and I have also seen healthy people have significant morbidity and even death as a result of invasive testing performed as a result of a positive screening test.  Screening tests have to be a joint decision between doctor and patient, once the potential benefits and risks are understood. Hopefully the years to come will produce sensitive and specific screening tests for more cancers and other health conditions. Talk to your doctor about what screening tests make sense for you.

Published Guidelines

https://www.uspreventiveservicestaskforce.org/Page/Name/uspstf-a-and-b-recommendations/

 

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