Types of Genetic Testing Explained: Carrier, Diagnostic, Predictive and Pharmacogenomic

Genetic testing guide · 2026

Genetic tests are frequently sold as one category. They answer entirely different questions, and choosing the wrong one wastes both money and the opportunity to get a real answer.

By MedEx · Updated September 2026 · Approx. 9-minute read

Quick answer

Genetic testing is not one thing. Carrier testing asks whether you could pass a recessive condition to a child. Diagnostic testing asks whether a genetic condition explains symptoms you already have. Predictive and presymptomatic testing asks about future risk in someone currently well. Prenatal testing asks about a pregnancy. Pharmacogenomic testing asks how you are likely to metabolise particular medicines. Direct-to-consumer ancestry and wellness tests answer a different question again, and are not clinical-grade. Matching the test to the question is the whole exercise.

In this guide

1. The categories, side by side
2. Matching the test to the question
3. Direct-to-consumer tests: what they are not
4. Why counselling is part of the test

The categories, side by side

Available options are listed on the MedEx genetic testing services page.

Matching the test to the question

“We are planning a pregnancy.” Carrier screening — in Thailand, thalassaemia screening first.

“I am pregnant and want to know about chromosomal conditions.” NIPT for screening, CVS or amniocentesis for diagnosis. See MedEx NIPT services.

“There is a strong family history of cancer.” Predictive testing, ideally starting with the affected relative where possible, since knowing which variant runs in the family makes testing others far more informative.

“My child has unexplained developmental delay.” Diagnostic testing, usually chromosomal microarray and often exome sequencing, arranged through a clinical genetics service.

“Antidepressants have not worked for me.” Pharmacogenomic testing may contribute, though it is one input rather than an answer, and the evidence varies considerably by drug.

“I want to know my ancestry.” A consumer ancestry test — but understand that these are not clinical-grade and their health reports should not be used for medical decisions.

Direct-to-consumer tests: what they are not

Consumer genetic tests are genuinely interesting and inexpensive, but their health claims warrant scepticism.

• They test selected variants, not genes comprehensively. A consumer BRCA report may test a handful of variants out of thousands known to be pathogenic, so a “negative” result offers far less reassurance than a clinical test.
• False positives occur. Studies of raw consumer data reanalysed in clinical laboratories have found a meaningful proportion of reported risk variants to be incorrect.
• Wellness and nutrigenomic reports — on diet, exercise response and supplement needs — generally rest on weak evidence.
• Third-party interpretation tools applied to raw data frequently generate alarming and unreliable output.

If a consumer test has produced a concerning health result, the appropriate step is confirmation in a clinical laboratory with counselling, not a decision based on the report. Book a specialist teleconsultation.

Why counselling is part of the test

Genetic results differ from most laboratory results in three ways that make counselling more than a formality.

They involve your family. A result about you is partly a result about your siblings, parents and children, who may not have chosen to know.

They can be uncertain. A variant of uncertain significance is a real and common outcome — a change whose meaning is not yet known. Understanding in advance that this is possible prevents considerable distress.

They may be unactionable. Some predictive results identify risk for which no effective intervention exists. Whether you want that information is a personal decision, and one worth making before testing rather than after.

Good practice is a conversation before the test as well as after. Arrange through MedEx doctor consultations or the genetic testing team.

Frequently asked questions

What is the difference between carrier and diagnostic genetic testing?

Carrier testing is for healthy people and identifies recessive variants that matter only in combination with a partner’s. Diagnostic testing is for someone with symptoms and aims to identify a genetic cause that explains them.

What is predictive genetic testing?

Testing someone who is currently well for a condition they may develop later, often because of family history – for example BRCA testing or testing for an inherited cardiac condition. Counselling is essential because results can be life-altering.

Are direct-to-consumer genetic tests reliable for health information?

Their health reports should not be used for medical decisions. They test selected variants rather than genes comprehensively, false positives occur, and wellness and nutrigenomic reports generally rest on weak evidence.

What is a variant of uncertain significance?

A genetic change whose clinical meaning is not yet known. It is a common and legitimate outcome of genetic testing, and understanding that it is possible before testing prevents considerable distress.

Is pharmacogenomic testing useful?

It can contribute to prescribing decisions for certain medicines, particularly in psychiatry, cardiology and oncology, but the evidence varies considerably by drug and it is one input rather than an answer.

Why does genetic testing need counselling?

Because results involve your family as well as you, can be uncertain, and may identify risk for which no effective intervention exists. Deciding what you want to know is best done before testing rather than after.

Sources and further reading

1. ACMG: Medical genetics practice resources
2. MedEx genetic testing services
3. ACOG Committee Opinion: Carrier Screening in the Age of Genomic Medicine

Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.