Diagnosing Cancers Through A Blood Test

Diagnosing cancer is difficult.

Cancer is a group of diseases in which healthy cells in our body undergo DNA changes. This affects the cell's programming, and instead of performing its regular functions, it begins to divide. Uncontrollably. This division causes greater and greater growth that uses up valuable resources and nutrition, destroys the healthy organs around it, and ultimately puts the body under so much strain it can cause death.

How do we diagnose cancer? If we are lucky we may notice unusual new symptoms. Unintended weight loss, excessive tiredness, bleeding from unusual places, difficulty breathing. It depends on the type of cancer. For some cancers, we have screening programmes, where we look for signs of cancer in people we know are at higher risk. But most of the time the symptoms are only detected when the cancer is advanced enough to cause damage to the body.

In some cases it can already be too late. Pancreatic cancer is notorious for not showing signs until the cancer is too advanced to operate, leaving patients with just 3-6 months of life expectancy.

If we recognise the symptoms we still need to run scans to see the size of the tumour, where it is, and obtain biopsies. Biopsies are vital in figuring out exactly what type of cancer is present, what medications would work against it and what the patients prognosis may be. Whether its by cutting out parts of the tumour directly, with a needle or with endoscopes, biopsy procedures are invasive, uncomfortable and sometimes painful.

What if there was a different way? What if you could take a blood sample and find out if a person has cancer? This dream is becoming slowly more and more real.

CIRCULATING TUMOUR DNA

Circulating Tumour DNA (ctDNA) is found in the blood and refers to DNA that comes from cancerous cells and tumours. Normally this is contained within the centre of a cell, in its nucleus. As a tumour grows, some cancerous cells can die and break apart. When this happens the contents of the cell are released into the blood, including pieces of the mutated DNA. Detecting this DNA is helpful for many reasons.

It can diagnose a tumour based off the mutations present on the DNA. Different cancers will have different mutations, and matching these up can show whether cancer is present before it starts showing symptoms
If we know cancer is present, we can use the DNA to create personalised medical therapy that is specific to one particular cancer in that particular individual. In the future, this could lead to a therapy that does not have as many side effects as chemo and radiotherapy
Repeated blood tests during treatment to look at levels of ctDNA could show whether the treatment is working. A decrease in ctDNA levels would correspond to a decrease in tumour size
Similarly, a lack of ctDNA would show treatment was successful, and the patient is remission free.

This all seems too good to be true. One blood test and you could know if you have cancer years before your symptoms start forming.

In July 2020 an international team of researchers published a study showing a non-invasive blood test was able to detect whether a person had one of five common types of cancer, up to four years before cancer would otherwise have been detected through our current methods. Stomach, oesophageal, colorectal, lung and liver cancer were the types included in the study.

It had a 91% success rate in patients who were otherwise asymptomatic, and 88% successful in detecting cancer in patients who were known to have cancer. If the test states you don’t have cancer, it was shown to be 95?curate.

This incredible study took over 10 years to conduct with over 120,000 participants who gave blood samples at regular intervals, as well as regular check in with physicians to monitor symptoms. Over 1.6 million specimens were collected and archived for this gargantuan project.

Specialists not involved with the research project have praised it, saying its methods are robust and the test is an essential first step towards commercial cancer screening. Of course, we still have many years and lots more research to do before we can achieve this goal, but the results are exciting nonetheless.

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Fever for 3 Days ? Should You Visit a Doctor or Wait

A fever lasting three days raises valid concern for patients and caregivers alike. While many febrile episodes resolve independently, a persistent fever lasting 72 hours warrants careful evaluation. Understanding when to seek medical attention and when watchful waiting is appropriate can prevent unnecessary complications and guide timely clinical intervention.

Should You Visit a Doctor If Fever Lasts for 3 Days?

A fever persisting for three consecutive days in adults generally requires medical evaluation, particularly when body temperature exceeds 103°F (39.4°C) or when additional symptoms such as breathlessness, severe headache, or rash are present. In children under five years, medical consultation is recommended after 48 to 72 hours of unresolved fever regardless of severity. Physicians advise against self-managing a three-day fever without professional assessment in high-risk populations.

Clinically, a three-day fever threshold is significant because most viral infections producing fever resolve within 48 to 72 hours. Fever persisting beyond this window may indicate a bacterial infection, an underlying inflammatory condition, or a secondary complication requiring targeted diagnostic workup. In the Indian clinical context, endemic infections such as dengue, typhoid, and malaria must be considered as potential etiologies when fever extends beyond 72 hours.

Common Causes of Persistent Fever in Adults and Children

Persistent fever lasting three or more days may originate from a range of infectious and non-infectious etiologies. Identifying the underlying cause is essential for selecting appropriate treatment.

Infectious Causes:

Viral infections: Influenza, dengue fever, chikungunya, COVID-19
Bacterial infections: Typhoid fever (enteric fever), urinary tract infections, pneumonia, tuberculosis
Parasitic infections: Malaria (particularly relevant in tropical regions of India)

Non-Infectious Causes:

Autoimmune or inflammatory conditions
Drug-induced fever (fever as an adverse drug reaction)
Post-vaccination fever (typically resolves within 48 hours)

Condition	Typical Fever Duration	Key Associated Symptoms
Viral fever	3 to 5 days	Body ache, fatigue, runny nose
Dengue fever	5 to 7 days	Severe joint pain, rash, low platelet count
Typhoid fever	7 to 14 days	Abdominal pain, diarrhea or constipation, rose spots
Malaria	Cyclical pattern	Chills, sweating, rigors
Urinary tract infection	Variable	Burning urination, flank pain

What to Do When Fever Does Not Go Down After 3 Days

When fever does not subside after 72 hours, the immediate recommended course of action is to consult a general physician or internist for clinical assessment. Antipyretic medications such as paracetamol (acetaminophen) can manage symptom discomfort but do not treat the underlying cause. Blood investigations including a complete blood count (CBC), malarial antigen test, and dengue NS1 antigen test are standard first-line diagnostics in India.

Beyond seeking medical consultation, patients should maintain adequate hydration, rest, and nutritional intake. Oral rehydration is particularly important in a tropical climate where fever accelerates fluid loss. Specialists caution against self-prescribing antibiotics without laboratory confirmation, as indiscriminate antibiotic use contributes to antimicrobial resistance, a significant public health concern in India. Clinical data supports early laboratory testing as the most effective step when fever persists beyond three days.

Warning Signs That Require Immediate Medical Attention

Certain symptoms accompanying a three-day fever indicate medical emergencies requiring immediate hospital evaluation rather than home management.

Patients or caregivers should seek emergency care if any of the following are present:

Fever above 104°F (40°C) that does not respond to antipyretics
Severe headache with neck stiffness (possible meningitis)
Difficulty breathing or chest pain
Skin rash appearing alongside fever (possible dengue or viral exanthem)
Altered consciousness, confusion, or seizures
Persistent vomiting preventing oral hydration
Fever in infants below three months of age
Fever in immunocompromised patients (those on chemotherapy, steroids, or with HIV)
Signs of dehydration: sunken eyes, dry mouth, reduced urine output

In children, febrile seizures can occur at temperatures above 102°F (38.9°C). While often self-limiting, any seizure associated with fever requires urgent pediatric evaluation.

Can a 3-Day Fever Resolve Without Medical Treatment?

In otherwise healthy adults, a mild to moderate fever (below 102°F) lasting three days caused by a self-limiting viral infection can resolve without specific medical treatment. The immune system typically clears common viral pathogens within three to five days. Supportive care including rest, hydration, and antipyretics is sufficient in low-risk cases.

However, resolution without medical treatment is not advisable for children under five, adults above 65, pregnant women, or individuals with chronic conditions such as diabetes or heart disease. Clinical evidence consistently indicates that delayed diagnosis in these populations increases the risk of serious complications. In regions with high prevalence of vector-borne diseases such as dengue and malaria, assuming a self-limiting viral cause without testing carries significant risk. Medical consultation remains the safest and most clinically sound approach when fever persists beyond three days.

Medical Disclaimer

This content is intended for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Readers experiencing persistent fever or related symptoms should consult a qualified healthcare professional for evaluation and management.

If you are facing similar health concerns, consult expert doctors online through the SecondMedic app or visit your nearest SecondMedic Health Hub for in-person care

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