companion diagnostics


companion diagnostics

Laboratory tests and test kits used to determine the suitability of patients for tailored or targeted forms of therapy, e.g., therapies that act on unique biochemical pathways or that require specific genotypes or mutations. See also: diagnostics

Genetic Testing

Synonym/acronym: Related terms: personalized medicine, companion diagnostics, molecular diagnostics.

Common use

To assist in the identification of genetic mutations with implications regarding health and treatment decisions.

Specimen

The facility or testing laboratory should be contacted regarding specimen collection requirements. Possible specimen types include whole blood, buccal samples, and tissue samples.

Normal findings

Method: Methods are specific to the study of interest and preferred specimen type. Methods include polymerase chain reaction (PCR), immunohistochemical assay, DNA probe using fluorescence in situ hybridization (FISH), gene amplification using chromogenic in situ hybridization (CISH), cell culture with karyotyping. Absence of findings consistent with genetic abnormalities related to disease or the ability to metabolize medications normally.

Description

Genetic testing has become an important piece of the continuously evolving health-care model. It is now possible to identify diseases before symptoms appear, predict the likelihood of disease development, and implement lifestyle or therapeutic interventions that will reduce or eliminate the effects of disease. Closer investigation into the nature of disease has sometimes revealed a more complex set of interactions than what was previously understood. While human DNA has similarities, there are also many individual differences. Additionally, there are numerous factors such as diet, activity, environment, and stress levels that contribute to variations between one individual and another. These factors in combination with our genetic makeup impact our tendency toward the development of illnesses. Technologies made possible through the accomplishments of the Human Genome Project and a multitude of findings from other collaborative research efforts have resulted in an explosion of diagnostic and prognostic information. The subspecialty of microbiology has been revolutionized by molecular diagnostics. Molecular diagnostics involves the identification of specific sequences of DNA. Molecular methods are used to help identify pathogens that were previously undetectable or inconsistently identified by the culture and biochemical methods available at the time. Molecular methods are also used to examine human samples for genetic disorders that are the result of both simple and complex mutations. Areas of great interest and active development related to genetic testing are in microbiology, virology, oncology, and the development of pharmaceuticals. Diagnostic and biotechnology companies are developing assays to identify gene sequences that code for proteins associated with a specific disease. Notable examples include the following:

  • Mutations in the epidermal growth factor receptor (EGFR) gene: The gene encodes a protein (EGFR) associated with many types of cancer including lung, breast, and colorectal cancer.
  • Mutations in the KRAS gene: If mutations are present, specific medications used to treat lung, breast, and colorectal cancers will be rendered ineffective; therefore, other options can more immediately be considered.
  • Mutations in HER-2–NEU gene associated with breast cancer: If mutations are present, the cancer risk can be stratified, survival can be predicted, and selection of treatment options can be made.
  • Mutations in the BRAF gene: If present, the mutations are used to identify patients, with cancers such as melanoma, who might benefit from treatment with specific drugs that are known to be effective.
  • Mutations in the P450 cytochrome series: If present, the mutations are used to predict response to specific drugs—some people will be poor metabolizers (requiring adjustments to higher doses) and some people will be ultrasensitive metabolizers (requiring adjustments to smaller doses).
  • Factor V Leiden mutation: If present, this mutation indicates the person has a higher than normal risk for thromboembolism.
  • Mutations in the BRCA1 and BRCA2 genes: If present, this mutation indicates the person has a high risk for development of hereditary breast or ovarian cancer. This knowledge provides the opportunity to make informed decisions regarding prophylactic mastectomy or oophrectomy.
New assays are either being developed after an effective therapy for the disease has also been developed or at the same time the treatment is being developed, as companion diagnostics. The cost-benefit analysis for the development of companion diagnostics makes a clear case for the simultaneous development of tests and targeted therapies rather than application by trial and error. The companion diagnostics model is based on the development tests that identify diseases or their related pathways, from genetic expression to production and interaction of proteins, and then to development of specific related therapies that are predicted with confidence to be effective.

Personalized medicine is the combination of identifying specific knowledge about an individual’s genetic makeup with customized therapeutics or adjustments in lifestyle, for example, genotyping for single nucleotide polymorphisms (SNPs). A SNP, or variation of a single nucleic acid in a DNA sequence, has been identified that causes malfunction of an enzyme needed for the metabolism of warfarin. Identification of this genotype has led to the development of algorithms for safe, tailored dosing and administration based on a patient’s genotype, age, weight or body mass index (BMI), and gender. Personalization can also be achieved in the customized production or compounding of pharmaceuticals with respect to the strength or formulation of the medication. Customized pharmaceuticals are being used to address dosing issues revealed by the presence of mutations in the CYP 450 series; adverse drug reactions either by undermedication or overmedication are sometimes the result of genetic programming rather than a medication error.

The System Tables at the back of the book designate the individual monographs that contain information regarding specific genetic testing.

This procedure is contraindicated for

  • high alert Patients who are not capable of comprehending information presented in the pre- and post-testing genetic counseling sessions. The test should not be performed if the parents of an affected born or unborn child, or if the patient himself or herself, is not emotionally capable of understanding the test results and managing the ramifications of the test results. Written and informed consent, in combination with additional education and a support system, are crucial in order to prepare the patient to make life-altering decisions.

Indications

  • Assist in confirming the diagnosis of conditions associated with genetic disorders before or after associated symptoms are manifested.
  • Assist in determining drug selection and appropriate dosing on an individual basis.
  • Assist in forensic identifications or paternity determinations.
  • Assist in monitoring the efficacy of therapeutic interventions.
  • Determine the probability of passing a heritable disease to unborn children; discuss prenatal planning.
  • Establish a predisposition for the development of certain diseases.
  • Identify matches for organ donation.
  • Identify agents of infectious disease.
  • Provide an explanation of death (e.g., miscarriage, stillbirth).
  • Screen for a genetic disease or condition that may affect an embryo, fetus, or neonate.

Potential diagnosis

Identification of a condition or disease based on the results of specific genetic testing. Identification or disqualification of therapies related to a condition or disease based on the results of specific genetic testing.

Critical findings

  • N/A

Interfering factors

  • Proper specimen handling and transport are crucial in order to provide accurate results. The laboratory should be consulted regarding specific instructions prior to specimen collection, especially since tissue specimens are considered irretrievable.

Nursing Implications and Procedure

Potential nursing problems

N/A

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in assessing for infection or disease using genetic testing.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s immune and related systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that several tests may be necessary to confirm the diagnosis. Inform the patient that specimen collection depends on the type of specimen required for testing. Address concerns about pain and explain that there may be some discomfort during specimen collection. (See related monographs for specific information.)
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • See the related monographs regarding special instructions for patient preparation.
  • Make sure a written and informed consent, if required, has been signed prior to specimen collection.

Intratest

  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Contact the testing laboratory prior to specimen collection in order to obtain accurate information regarding specimen collection containers, sample volumes, and specific transport instructions.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Collect the appropriate specimen as described in the related body fluid analysis or culture monograph. The facility or testing laboratory should be contacted for guidelines regarding specimen collection requirements, and specimen packaging and shipping instructions.
  • Perform a venipuncture if blood is the specimen required for testing. Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation, and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Recognize anxiety related to test results, and provide emotional support if results are positive. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
  • Note that depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed. Emphasize the need to return to have additional samples taken, if ordered. Answer any questions or address any concerns voiced by the patient or family.

  • Patient Education

      N/A

  • Expected Patient Outcomes

      N/A

Related Monographs

  • Related tests include α1-antitrypsin, Alzheimer’s disease markers, amino acid screen blood & urine, amniotic fluid analysis, antibodies gliadin, anticonvulsant drugs, antidepressant drugs, antipsychotic drugs, biopsy breast, biopsy chorionic villus, biopsy skin, biopsy thyroid, bladder cancer markers, cancer antigens, CD4/CD8 enumeration, chlamydia group antibody, chloride sweat, chromosome analysis, coagulation factors, CBC platelet count, culture and smear mycobacteria, culture bacterial (anal/genital, ear, eye, skin, and wound), cytomegalovirus, fecal analysis, glucose, group A strep screen, hexosaminidase A & B, human leukocyte antigen B27, immunosuppressant drugs, leukocyte alkaline phosphatase enzyme, newborn screening, parvovirus B19, prothrombin time and INR, red blood cell cholinesterase, and varicella antibodies.
  • Refer to the Gastrointestinal, Genitouri-nary, Hematopoietic, Hepatobiliary, Immune, Musculoskeletal, and Respiratory System tables at the end of the book for related tests by body system.