Infectious Disease & Molecular Testing
Infectious diseases are caused by microorganisms such as bacteria, viruses, fungi, and parasites. They can affect almost any organ system and may range from common community-acquired infections to serious infections requiring rapid diagnosis and targeted treatment.
Laboratory testing plays an important role in identifying infectious organisms, confirming infection, assessing disease activity, detecting antimicrobial resistance, and monitoring treatment response. Modern infectious-disease diagnostics increasingly combine microbiology, serology, antigen testing, culture, antimicrobial susceptibility testing, and molecular techniques such as PCR and real-time PCR.
At National Path Lab (NPL), specialized laboratory investigations are available to support the diagnosis, monitoring, and management of selected infectious diseases.
Conditions (13)
About Infectious Disease & Molecular Testing
Testing Areas Covered on This Page
• Respiratory Infections
• Tuberculosis
• Hepatitis B
• Hepatitis C
• HIV Infection
• Sexually Transmitted Infections (STIs)
• Human Papillomavirus (HPV) & Cervical Cancer Screening
• Dengue
• Malaria
• Enteric & Gastrointestinal Infections
• Urinary Tract Infections
• Bloodstream & Systemic Infections
• Antimicrobial Resistance
• Congenital & Perinatal Infections
• Pediatric & Neonatal Infections
• Central Nervous System Infections
• Infection in Immunocompromised Patients
What Is Molecular Testing in Infectious Diseases?
Molecular testing detects the genetic material of an infectious organism. Depending on the test, molecular assays may detect DNA, RNA, pathogen-specific genetic sequences, or selected antimicrobial resistance markers. PCR and real-time PCR are commonly used molecular techniques.
Molecular testing can be particularly useful when rapid detection is important, the organism is difficult to culture, prior antimicrobial treatment may affect culture results, a specific pathogen is strongly suspected, or viral load needs to be quantified.
PCR vs. Culture
Both molecular testing and culture have important roles in infectious-disease diagnosis. Molecular testing offers rapid detection, high analytical sensitivity for selected targets, detection of organisms that may be difficult to culture, and detection of selected resistance markers. Culture provides growth of viable organisms, organism identification, and antimicrobial susceptibility testing.
The appropriate method depends on the organism, specimen, and clinical question. In many situations, molecular and conventional microbiological methods complement each other rather than replace one another.
Qualitative vs. Quantitative Molecular Testing
Molecular infectious-disease tests may be qualitative or quantitative. Qualitative PCR answers: "Is the target pathogen genetic material detected?" — the result is generally reported as detected or not detected. Quantitative PCR answers: "How much target genetic material is present?" — results may be expressed as a viral load or other quantitative measurement depending on the assay. Quantitative testing is particularly useful for selected chronic viral infections such as HBV and HCV.
Why Is Infectious Disease Testing Sometimes Done as a Combination?
Infectious diseases can produce overlapping symptoms. For example, fever, cough, and fatigue may occur with viral infections, bacterial infections, tuberculosis, and other conditions. Doctors may therefore combine clinical examination, routine laboratory tests, culture, serology, antigen testing, molecular testing, and imaging — different tests answer different clinical questions.
A positive molecular result does not always mean that the detected organism is the cause of the patient's current symptoms. Results must be interpreted together with the clinical presentation and specimen type.
Why Is the Correct Specimen Important?
The specimen collected for an infectious-disease test should represent the suspected site of infection. Depending on the disease, specimens may include blood, urine, sputum, nasal/nasopharyngeal swab, throat swab, stool, CSF, or other validated clinical specimens. For molecular testing in particular, sample quality, timing relative to illness onset, and proper specimen handling can significantly affect test performance.
A Note on Emergency Presentations in This Document • Several topics in this document — bloodstream infection/sepsis, central nervous system infections, and serious infection in young infants — describe medical emergencies. • For these topics specifically, the 'Home Sample Collection' and 'When to See a Doctor' sections direct the reader to seek immediate emergency or hospital care, rather than describing a routine outpatient testing pathway. • This content must never be used to delay seeking emergency medical care for a person showing signs of serious illness. |
Home Sample Collection
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