Testing and Detection

Core Concepts

Categories of genetic tests

Genetic tests are best organized by the question they answer:

• Carrier testing — whether a symptom-free person carries one altered allele for a recessive condition (e.g., cystic fibrosis, sickle cell disease).
• Prenatal screening and diagnosis — screening (cell-free DNA in maternal blood, ultrasound markers) estimates fetal risk; diagnostic tests (chorionic villus sampling, amniocentesis) confirm or exclude it.
• Newborn screening — screening shortly after birth for treatable conditions (e.g., phenylketonuria, congenital hypothyroidism); a screen is a starting point, not a diagnosis.
• Diagnostic testing — used when a person has symptoms or findings, to confirm or rule out a suspected genetic condition.
• Predictive and presymptomatic testing — for symptom-free people with a family history of an adult-onset condition (e.g., Huntington disease); high-stakes, done with specialized counseling.
• Pharmacogenomic testing — gene variants that affect medication metabolism or response, to help guide drug and dose selection.

Laboratory methods at a glance

Different questions require different tools. A karyotype pictures the full set of chromosomes and detects extra, missing, or grossly rearranged ones. FISH uses labeled probes to find specific chromosome regions; chromosomal microarray detects smaller gains and losses of DNA; DNA sequencing reads the letter sequence of targeted genes or the whole exome; PCR-based tests copy specific segments so tiny amounts of a variant can be detected. The nurse does not run these tests — but must know a "genetic test" is not one thing; its resolution determines what it can find.

Screening versus diagnosis

Screening is applied to mostly well people at scale and produces a risk estimate — a "higher chance" result that must be followed by a diagnostic test. Diagnostic testing confirms or excludes a condition in a specific person. A positive screen is never a diagnosis; stating this clearly prevents both false alarm and false reassurance.

The testing process and test limitations

A responsible test follows a cycle: pre-test counseling (what the test can and cannot tell, possible results, implications for relatives), informed consent (voluntary, documented), sample collection (blood, saliva, buccal swab, amniotic fluid, or chorionic villi), analysis, result return (with support, usually by a genetics professional), and follow-up (referrals, cascade-testing discussion, surveillance planning).

Tests have limits. A variant of uncertain significance (VUS) is a DNA change whose effect on health is not yet known — not a diagnosis, not a verdict, and something families often need help understanding. A negative targeted test does not rule out every possible genetic cause, and a result meaningful in one family may not generalize to another. Nurses present results as information to interpret with the care team, never as a final pronouncement.

The nurse's role and ethical framework

The nurse's role is to educate, support, document, and refer — not to order tests, interpret results authoritatively, or decide for patients. Testing must be voluntary and non-directive: the patient decides, free of pressure from clinicians or family. Confidentiality is essential: genetic information belongs to the patient, and sharing it with at-risk relatives raises ethical questions handled under institutional policy and ethics consultation. Scope of practice, who may order and disclose results, and applicable laws vary by country, state, and institution.

Common Confusions