Fever profile blood tests: when to test for Dengue, Typhoid, or Malaria in Delhi
High fever with chills, body ache or headache during monsoon. Which day to test for NS1 vs Widal vs Malaria smear, and why tracking platelets matters.
Acute febrile illnesses are among the most common presentations in Delhi NCR, particularly during monsoon and post-monsoon months. When a temperature spikes, knowing which test to order and on which day of fever makes all the difference between a clear diagnosis and an ambiguous result.
The crucial role of timing in fever testing
Diagnostic antibodies and antigens appear at different stages of infection. Ordering a test on the wrong day can yield a false negative:
1. Dengue: NS1 Antigen vs IgM/IgG Antibody
- Days 1 to 5 of fever: Dengue NS1 Antigen is the test of choice. The virus is actively circulating in the bloodstream and NS1 is highly sensitive during this initial acute window.
- Day 5 onwards: As viral load decreases, the body produces Dengue IgM antibodies. Testing for both NS1 and IgM together (Dengue Combo) ensures you catch the infection regardless of exact day estimation.
- Platelet monitoring: A Complete Blood Count (CBC) is essential to track platelet count and Packed Cell Volume (PCV/Haematocrit). In dengue, doctors monitor the downward trend rather than a single absolute value.
2. Typhoid (Enteric Fever): Typhidot vs Widal
- Week 1 of fever: Typhidot (IgM & IgG) detects early outer membrane protein antibodies of Salmonella typhi, often turning positive within 3–5 days of fever onset.
- Week 2 of fever: The traditional Widal tube agglutination test measures O and H antibody titres, which typically rise only after 7 to 10 days of continuous step-ladder fever.
3. Malaria: Antigen & Peripheral Smear
- Malaria (Plasmodium vivax and Plasmodium falciparum) presents with high fever, shaking chills (rigors), and profuse sweating.
- A rapid malaria antigen test combined with a Giemsa-stained peripheral blood smear (thick and thin smear) is the gold standard, best drawn immediately during or following a fever spike.
Why a CBC and CRP are the foundational first step
When fever starts, doctors routinely begin with:
- Complete Blood Count (CBC): Reveals whether total white blood cells (WBC) are depressed (common in dengue and viral infections) or elevated with high neutrophils (bacterial infections).
- C-Reactive Protein (CRP): A sensitive inflammation marker that rises rapidly in bacterial infection and helps gauge systemic severity.
When to seek emergency medical care
Do not wait for a home collection slot if the patient exhibits red-flag signs:
- Platelet count falling below 50,000 / μL
- Persistent vomiting, severe abdominal pain, or inability to retain fluids
- Bleeding from gums, nose, or unusual dark stools (melena)
- Extreme lethargy, confusion, or difficulty breathing
General medical information, not personal medical advice. Consult your doctor promptly for fever evaluation and treatment.
Tests mentioned in this guide
Common questions
Which day of fever should I test for Dengue?
Dengue NS1 Antigen is most effective on Days 1 to 5 of fever. Dengue IgM antibody becomes reliable from Day 5 onwards. A Dengue Combo panel tests both simultaneously.
Is fasting required for fever blood tests?
No. CBC, Dengue, Typhoid, Malaria, and CRP tests do not require fasting and can be given at any time of day.
How often should platelet count be monitored in Dengue?
Depending on your doctor advice and initial count, CBC is typically repeated every 12 to 24 hours during the critical fever phase (Days 3 to 7).
Can I take pain relief tablets before testing?
Paracetamol is standard for fever. Avoid NSAIDs like ibuprofen, mefenamic acid, or aspirin unless approved by your doctor, as they increase bleeding risks.