Rapid Test Results Give Physicians Edge Over Strep
Edition: November 2002 - Vol 10 Number 11
In this fast-paced culture, where people demand immediate feedback and quick results, your customers and their patients are no exceptions.
If not diagnosed early, group A streptococcus (GAS) can spread easily. Although it usually involves mild symptoms such as headache, fever or abdominal pain, if left untreated, this bacterial infection can become more severe and even deadly. Physicians often rely on fast diagnosis, and particularly for their patients who can spread the germ easily through schools and playgrounds.
Rapid vs. Throat Culture
In spite of the degree of accuracy that rapid tests offer, some physicians waver over the benefits of these tests compared with traditional throat cultures. Generally, rapid strep tests – which can be stored at room temperature and generate results in about five minutes – are attractive to patients who can’t afford to miss a day or two from work or school, waiting for the results of a throat culture. When rapid strep test results are positive, antibiotic treatment can be administered immediately, before the virus is spread too widely. Within 24 hours after starting an antibiotic program, the patient can interact with other people.
Rapid strep tests also are useful when an individual has been exposed to group A strep during an epidemic of rheumatic fever, or for patients with a family history of rheumatic fever or other serious forms of group A strep, according to WebMD™Health. In addition, rapid tests generally cost less than throat cultures.
Still, some physicians stand firm that no test is as accurate as a throat culture. Sometimes, depending on the severity of a patient’s symptoms, the physician will order a follow-up throat culture even when the results of the rapid test are negative. In these cases, the expense of two tests is greater than performing a throat culture at the start, and the patient still needs to wait for a day or two to learn the results. In addition, some physicians believe that having a patient wait a day or two before starting antibiotic treatment allows the body to build up its immune system to the GAS germ. And, as long as antibiotic treatment is started within nine days after symptoms appear, the patient should not develop rheumatic fever, notes WebMD™Health.
Rapid Tests Prove Dependable
No matter which approach – rapid or throat culture – physicians support, the efficiency and dependability of rapid tests cannot be discounted. Two years ago, when the Journal of Family Practice cited a study on the validity of rapid strep tests without follow-up throat cultures, results suggested that there is no difference in the complication rate between patients tested with a rapid test over a throat culture (Webb KH, Needham CA, Kurtz SR. Use of a High-sensitivity Rapid Strep Test Without Culture Confirmation of Negative Results. J Fam Pract 2000; 49:34-8).
The researchers identified 30,036 patients diagnosed with pharyngitis over a four-year period. During the first two years of study, patients were tested using bacterial throat cultures. Over the latter two-year period, patients were tested using BioStar Inc.’s (currently Louisville, CO-based ThermoBioStar) Strep A OIA high-sensitivity rapid test. The researchers compared the rates of complications from pharyngitis between the two patient groups, and found no difference.
Today, rapid tests offer accuracy rates as high as 98 percent. Generally, tests involve swabbing the patient’s throat, adding the swab to a test tube with a reagent mixture, and then placing a dipstick into the solution for about five minutes to yield results. One example of how the test works is San Diego, CA.-based Quidel Corp.’s QuickVue® Dipstick Strep A test. The test involves a lateral-flow immunoassay, which relies on Quidel-patented antibody-labeled particles. The test detects either viable or nonviable organisms from the patient’s throat swab.
To perform the test, the technician first adds three drops of Reagent A and three drops of Reagent B to a clean tube. The solution should turn green. (If the solution is green prior to adding Reagent B, the technician must contact Technical Support for direction, notes Quidel.)
Next, the technician collects a throat swab specimen from the patient. This is accomplished by depressing the tongue with a blade or spoon, and rubbing the swab on the back of the throat, on the tonsils or in areas that appear red, inflamed or covered by pus. The technician must not allow the swab to touch the tongue or the sides or top of the patient’s mouth. Quidel recommends using rayon-tipped swabs on solid plastic shafts, which are included in the test kit. Calcium alginate, cotton-tipped, hollow shaft or wooden shaft swabs should not be used. If the physician plans to follow up with a throat culture, the swab with specimen should be lightly streaked on a five percent sheep blood agar plate before it is used in the dipstick test. (If the swab is used in the test first, the test solution will destroy the bacteria specimen and the organism will not be able to be cultured later on.)
After collecting the specimen, the technician adds the sample to the tube. To ensure the most accurate results, the technician should squeeze the bottom of the tube to compress the swab head. The swab must then be rotated at least five times and left in the tube for a full minute. All liquid should be expressed from the swab against the inside of the tube, and the swab should be squeezed firmly as it is removed from the tube. The technician must discard the swab immediately.
The technician then removes the dipstick from its protective foil pouch and places it into the tube with the arrow markings pointing down. The dipstick should remain untouched for at least five minutes when the test is complete. Some positive results may appear sooner, according to Quidel.
Results may be read as follows:
· Positive. A pink to purple test line is visible, along with a procedural control line in any shade of blue.
· Negative. A blue procedural control line appears, with no pink test line.
· Invalid. A blue control line is not visible within five minutes. In this case, the patient must be retested using a new sample and dipstick.
Recommended CPT codes for the QuickVue® Dipstick Strep A and similar tests are 87880 and 87880QW for CLIA-waived products for Medicare and Medicaid patients. The 2002 national fee average ranges from $7 to $25, according to Quidel.
Other rapid strep tests available to physicians include:
· Abbott Laboratories SIGNIFY Strep A. A CLIA-waived 50-test kit featuring 96 percent sensitivity and product dating up to 12 months.
· Beckman Coulter ICON® Fx Strep A test. A CLIA-waived test with on-board extraction, eliminating the need for standing tubes and pipettes. Sensitivity is 92 percent and specificity is 100 percent.
· ThermoBioStar Strep A OIA MAX. A 30-test kit that claims to detect more true positives than agar culture.
· Becton Dickinson Directigen™ 1-2-3 Group A Strep test. A two-minute start-to-finish test with 98 percent sensitivity and 95 percent specificity.
· Genzyme OSOM® Ultra Strep A.Clia-waived 25-test kit or 50-test kit (moderate). Sensitivity of Ultra Strep A test and standard single swab culture are not statistically significant. Two color results, easy to use dipstick format, and room temperature storage.
More information on these and other rapid strep A test is available from manufacturers and distributors.