Types of Covid Tests

Since the beginning of the pandemic, COVID-19 testing has played a critical role in helping people detect infections, protect loved ones, and prevent the spread of the virus. But with so many types of tests available — from PCR to rapid antigen to antibody tests — it’s easy to feel confused about which one does what, and when to use each one.   

What’s the difference between a PCR test and a rapid test? Can a blood test tell if you had COVID in the past? Which one is the most accurate? 

In this blog, we’ll break down the main types of COVID-19 tests, how they work, what they detect, and when they’re most useful — in simple terms anyone can understand. 

Whether you're testing for travel, returning to work or school, or just curious about your COVID history, this guide will help you understand which test is right for your situation. 

There are 3 Main types of Covid Tests, and they are classified by what they detect: 

• NAAT (Nucleic Acid Amplification Tests) - detects viral RNA 
• Rapid Antigen Test - detects Viral protein 
• Serology/Antibody Tests - detects Antibodies  

NAAT (Nucleic Acid Amplification Tests) 

Have you ever wondered how just a simple swab can detect COVID-19? 

It’s because of a diagnostic test called a NAAT, which stands for Nucleic Acid Amplification Test. NAATs are used to check if someone is currently infected with viruses like COVID-19, influenza, or HIV. NAATs are very sensitive and can find even tiny amounts of a virus in your body.  And, RT-PCR Tests PCR is the most well-known type of NAAT. 

What is RNA? And What does RNA have to do with COVID Tests? 

We all know DNA — it's like your body’s giant instruction manual, storing all the information needed to build and run you. 

Now here’s RNA: 

• RNA is like a smaller, working copy of DNA. 
• While DNA stores the full blueprint, RNA carries pieces of that blueprint or instructions to your cells — usually to make proteins. 

Now here’s an important key point: 

• Humans, viruses, and even bacteria carry their own RNA. 
• Viruses enter the human body carrying their own RNA (called viral RNA). 
• Viruses ‘disguise’ themselves like normal human RNA. 
• The cell is fooled and mistakes it for normal instructions. 
• The cell doesn’t know it’s a virus. It just sees RNA instructions. 
• The cell follows whatever the viral RNA says — which is more copies of viruses! 
• So when you swab your nose, your sample has: 
• Your own RNA (from your cells) 
•  Viral RNA (if the virus is present) 

What is Viral RNA? 

• This is the RNA that belongs specifically to the virus — like SARS-CoV-2 (COVID-19). 
• It’s the virus’s blueprint — the genetic code that helps it reproduce. 
• It’s what NAATs are trying to find. The test doesn’t care about your human RNA. 

How Does NAAT Work? 

The test starts by collecting a sample — usually from the nose, throat, or blood — where the virus is most likely to be found if someone is infected. 

NAATs work by checking if the sample contains the virus’s genetic material, which is also called viral RNA. But here’s the interesting part: if someone has the virus, there might only be a tiny amount of viral RNA in the sample — too little for lab machines to detect on their own. 

To solve this, the test uses a process to amplify or make millions of ‘copies’ of viral RNA. One common method is called RT-PCR (Reverse Transcription Polymerase Chain Reaction). 

• The “RT” part means the test first uses an enzyme to convert the virus’s RNA into DNA, because the PCR process can only copy DNA, not RNA. 
• Then the “PCR” part amplifies the DNA — making enough copies so that the virus can be detected if it's there. 

The entire process usually takes a few hours, but in some labs, results can be ready within 24 to 48 hours depending on demand and location. 

So, what’s happening in the RT-PCR COVID test? 

RT-PCR or other NAATs don’t just randomly detect “any virus” — they only detect the specific virus they are programmed to look for. 

A COVID RT-PCR test looks specifically for viral RNA that matches the COVID-19 virus or SARS-CoV-2 in your sample from nose or saliva. 

If even a tiny piece is there, through the RT-PCR method: it converts the virus’s RNA into DNA; and copies the DNA millions of times, enough so lab machines can detect it. 

RNA is unique to the virus — if the machine finds SARS-CoV-2 RNA in someone’s nose or saliva, it means: 

• ✅ The SARS-CoV-2 virus is present 
• ✅ The person is likely infected 

Why Is RT- PCR Tests PCR the most well-known type of NAAT?  

NAATs — especially RT-PCR tests — are known as the most popular, accurate and reliable COVID-19 tests. 

It was commonly used during COVID because it was the first reliable test used to detect the SARS-CoV-2 virus for reasons: 

• It was already available and trusted. 
• It had been used for years to find other viruses (like Influenza or HIV). 
• It was the most accurate, being able to detect even tiny amounts of the virus, even before symptoms showed. 
• Because the test is based on the virus’s genetic code (RNA), it detects the actual presence of the virus itself — not just surface proteins (like in antigen tests) or your body’s immune response (like in antibody tests).  
• This means there’s less chance of false negatives, which is why doctors and health authorities around the world trust it. 
• Other tests, like rapid antigen tests (RATs), came later. They were faster but less accurate, especially in the early stages of infection. 

Rapid Antigen Test 

Ever wondered how people are able to test for COVID-19 at home and get results in just 15 minutes? 

A Rapid Antigen Test is often called a RAT. It is also known as Lateral Flow Test or COVID-19 Rapid Test. 

It’s a portable diagnostic tool; and one of the fastest and most convenient way to check if someone is currently infected with the COVID-19 virus. Unlike NAATs (like RT-PCR), which look for the virus’s genetic material, antigen tests look for proteins on the surface of the virus — called antigens. 

Did you know that antigen tests existed long before COVID-19 pandemic? 

They were commonly used to detect illnesses like influenza, strep throat, and RSV, but were mostly limited to hospitals and clinics, handled by healthcare professionals using specialised tools. 

However, when COVID-19 emerged, the need for fast, large-scale testing skyrocketed. While RT-PCR remained the gold standard, it required lab processing and often took 24–72 hours to return results. 

In response, scientists developed COVID-specific rapid antigen tests that could deliver results in just 15–30 minutes, without the need for a lab. These tests were made easier to use, portable, and cost-effective — allowing them to be used in homes, schools, airports, aged care, and workplaces. 

By late 2020 and into 2021, governments around the world, including Australia’s TGA (Therapeutic Goods Administration), began approving RATs for self-use, marking a major shift in how everyday people accessed testing. 

What is Antigen? And What does Antigen have to do with COVID Tests? 

When people talk about COVID-19 testing, they often mention RT PCR tests (which detect viral RNA, as we talked about earlier). But there’s another popular test used around the world — and that’s the Rapid Antigen Test (RAT). 

Now, what is Antigen? 

• An antigen is a special marker or flag found on the surface of viruses, bacteria, or anything foreign to your body. 
• Each virus has its own signature antigen. 
• For SARS-CoV-2, this antigen is the spike protein found on the surface of the virus. 

So, what happens in a Rapid Antigen Test? 

A Rapid Antigen Test (RAT) works by identifying the virus directly from your sample, typically collected from your nose or throat. 

Specifically, it detects a piece of the virus called an antigen — a surface protein found on the outer shell of the virus. 

These tests come in ready-to-use kits, which usually include: 

• a sterile swab (for collecting the sample), 
• a tube with a liquid buffer solution, 
• a dropper cap, and 
• a test cassette that contains the chemical testing strip. 

 The test can be done at home without medical equipment, or with the help of a healthcare worker at a clinic, pharmacy, or testing station. 

Here’s how it works: 

• Your sample (usually mucus) may have virus particles if you’re infected. 
• The test kit includes a special solution that breaks open any virus particles present in the sample. 
• This process releases the virus’s outer layer, including the antigen. 
• The sample is then applied to a test strip, which contains pre-loaded antibodies. 
• These antibodies are designed to recognise and attach to the antigen — like a magnet sticking to metal. 
•  If the virus antigen is present, it sticks to these antibodies, triggering a chemical reaction.  
• That reaction causes a colored line to appear on the test strip — this line is used to let you know if you are infected or positive for that virus.  

 That’s why it’s called an antigen test — because it directly detects the virus’s surface protein, not its genetic code (RNA) or your body’s response (antibodies).  

How Do COVID Rapid Antigen Tests Use This? 

When you take a Rapid Antigen Test (RAT), you’re not looking for the virus’s RNA like in a RT-PCR test — you’re looking for its antigen, specifically the SARS-CoV-2's antigen.   

How Does COVID Rapid Antigen Test Work? 

When you use a COVID Rapid Antigen Test, you’re performing a fast, on-the-spot check to see if the SARS-CoV-2 antigen is present in your body. 

To begin, 

• You collect a sample by swabbing your nose or throat.  
• The swab is mixed into a special liquid (called a buffer). The buffer breaks open the virus and releases the spike protein (antigen). 
• You add a few drops of the liquid onto a test strip. The strip is designed to let the liquid flow across it naturally. 
• Inside the test strip, there are two important lines that are made to catch the COVID-19 antigen. 
• Test line – this area has antibodies that are made to catch the COVID-19 virus antigen (spike protein). 
• Control line – this catches any leftover test chemicals to show the test worked correctly. 
• If the antigen is there, it sticks to these antibodies and triggers a color reaction — forming the visible line. 
• The liquid keeps flowing and reaches the control line, which if a line appears, confirms that the test worked. 

This process is called immunochromatography: 

• Immuno = It uses antibodies to detect viral antigens. 
• Chromatography = It separates and moves the liquid through the strip using absorbent paper. 

So, what do the lines mean? 

• One line (control only) = Negative 
• Two lines (control + test) = Positive for COVID-19 virus 
• No control line = Invalid — test didn’t work properly 

So, what does a positive result mean? 

If the test detects the spike protein antigen, it means: 

• ✅ The SARS-CoV-2 virus is likely present in your body 
• ✅ You are probably infectious and should isolate 

Why Are Rapid Antigen Tests Popular? 

Rapid Antigen Tests became popular during COVID because they’re: 

• Fast – Results are ready in under 30 minutes 
• Easy to use – No lab equipment needed 
• Helpful for screening in homes, schools, workplaces, and travel 
• Best used when someone is symptomatic or has had close contact 

While not as sensitive as PCR (they can miss cases in the very early stages), RATs are very useful for detecting high viral loads — when someone is most likely to spread the virus. 

What makes it work so quickly? 

Unlike RT-PCR tests that detect the virus’s genetic code (RNA), RATs detect surface proteins — this makes them faster. 

Where to buy covid rapid antigen test kits? 

If you're looking for trusted COVID-19 testing options, MedCart offers a carefully curated range of quality rapid antigen test kits  — whether for home use, workplaces, schools, or aged care settings. 

We stock a variety of ARTG-listed test kits that meet Australian standards, including: 

• COVID-19 only test kits  
• 2-in-1 kits (COVID + Influenza A/B)  
• 3-in-1, 4-in-1, and 5-in-1 options (including combinations of COVID, Flu A/B, RSV, and more)  
• Both oral swab and nasal swab formats for different comfort levels  

MedCart partners with reputable suppliers to ensure you have access to test kits that are accurate, easy to use, and approved for self-testing where applicable. 

For more information or to explore the full range, visit MedCart's COVID Test Kit Collection. 

Serology/Antibody Tests 

Remember how viral RNA enters the body and tricks your cells into making copies of it? 

Your cells can’t tell whether RNA is from your body or from a virus. They just follow instructions — and viral RNA is sneaky enough to slip in without setting off alarms right away. 

That’s why viruses like COVID-19 can start replicating before your body even knows something is wrong. But after a while, your immune system picks up on signs that something’s off. 

That’s where antibodies come in. Once your immune system recognises that unusual 'sign’: 

• It realises the virus is an invader. 
• It starts fighting back by making antibodies and activating immune cells. 

 What are Antibodies? And What does Antibodies have to do with COVID Tests? 

• Antibodies are special proteins that lock onto the virus and help stop it from spreading. 
• Antibodies take 1–3 weeks to develop after infection — so this test can’t detect early infection  
• It’s not used to diagnose current COVID-19 cases  
• It’s useful for knowing if someone has been exposed to the virus or has developed immunity 

So what do COVID Antibody Tests do? 

A Serology Test, also called an Antibody Test, looks for those antibodies in your blood. These antibodies are evidence that your immune system has responded to the virus — either from a past infection or from vaccination.  

So if your antibody test is positive, it means: 

• ✅ You had COVID-19 sometime before 
• ✅ Or you may have developed antibodies from vaccination 

If it’s negative, it means: 

• ❌ You haven’t had COVID-19, or 
• ❌ It’s too early — your body hasn’t made detectable antibodies yet  

How does Covid Antibody test work? 

1. A blood sample is collected  

A small amount of blood is taken — either from a finger prick or through a vein in your arm (venous blood draw). 

The test is usually done in a clinic, pathology lab, or hospital 

2. Your blood is tested for COVID-19 antibodies 

The lab looks for specific types of antibodies: 

• IgM antibodies – which appear early after infection 
• IgG antibodies – which appear later and may last longer 

These are tested by mixing your blood with lab-made COVID-19 proteins. If antibodies are present, they’ll attach to them.  

3. A detection reaction occurs 

A solution is added that causes a color change or signal if antibodies are found. 

This tells the lab that your body has been exposed to the virus or vaccine and responded. 

4. You get your results 

Most antibody tests return results in 1 to 3 days, depending on the lab. 

Your report will usually tell you whether antibodies were found (positive) or not (negative). 

So Why Does an Antibody Test Use Blood and Not a Swab? 

Unlike other COVID tests — like PCR or Rapid Antigen Tests — which use a nose or throat swab to check for the virus itself, antibody tests look for your body’s response to the virus. 

That response is in the form of antibodies, which are found in the bloodstream, not in your nose or saliva. 

So to run an antibody test, a blood sample is needed — either from a small finger prick or a blood draw from your arm. The test then checks if your immune system has produced antibodies that match the COVID-19 virus.  

Can You Do a COVID Antibody Test at Home? 

Right now, most antibody tests require a blood sample that’s processed in a lab — so they’re typically done in medical settings. 

Some countries have approved home collection kits, where you prick your finger, collect a small blood sample, and mail it to a lab. However, at-home antibody tests are not as widely available or approved as home COVID antigen tests. 

In Australia, for example, antibody tests are generally not approved for home use and must be done by a healthcare professional or in a registered pathology lab. 

Why Is It Interesting? 

Antibody tests help researchers understand how many people have been exposed to COVID-19, even those who never showed symptoms. 

They’re also used to monitor immune response after vaccination or natural infection. 

Some people who didn’t even know they had COVID later test positive for antibodies — showing just how sneaky the virus can be.