Microbiology Test Indication and Retesting Interval 

HIV 1 & 2 Ab (Human Immunodeficiency Virus) 

1. Screening for HIV infection:

• Antenatal

• High risk individual: PWID, FSW, TG, MSM

• Infant born to HIV mothers

• Patient with STI

• Patient with tuberculosis

• Frequent blood transfusion (Thalassemia, HD), blood donors

• Individual requesting for screening

• Contact of HIV positive individuals. 

• Prison inmates

2. Confirmatory test (second sample): Rapid test positive

4. Associated illness:

• Altered mental status (meningoencephalitis, dementia)

• Atypical pneumonia (eg: Mycoplasma)

• Recurrent bacteremia

• Prolonged skin rashes

• Peripheral neuropathy 

90 days 

*Depending on clinical indications, earlier retesting may be necessary. Please consult with a Clinical Microbiologist for further discussion on early testing.

HAV Ab IgG (Hepatitis A Virus IgG) 

Deranged liver enzymes accompanied by suggestive symptoms such as nausea, vomiting, anorexia, fever, malaise, abdominal pain, jaundice and pruritus

No repeat necessary unless there is re-exposure or new symptoms arise. 

HAV Ab IgM (Hepatitis A Virus IgM) 

Deranged liver enzymes accompanied by suggestive symptoms such as nausea, vomiting, anorexia, fever, malaise, abdominal pain, jaundice and pruritus

90 days.

*Depending on clinical indications, earlier retesting may be necessary. Please consult with a Clinical Microbiologist for further discussion on early testing..

HBc Ab Total / Anti-HBc Total (Hepatitis B core) 

1. HBsAg is non reactive/low reactive

2. Patient planned for immunosuppressive  therapy / chemotherapy/ immune modulator

90 days

If Positive, Anti-HBc will remain reactive for life. Hence,no repeat testing is required. 

HBc Ab IgM (Hepatitis B core IgM) 

1. Anti-HBc II reactive

2. TRO flare/acute on chronic 

90 days

HBe Ag (Hepatitis B e Antigen) 

1. HBsAg reactive

2. Assessment of infectivity/transmission risk

3. Baseline evaluation of Hepatitis B patient

4. Monitoring response to antiviral therapy

90 days

HBe Ab (Anti-HBe / Hepatitis B e Antibody) 

Monitoring response to antiviral therapy.

Assessment of disease phase in chronic hep B.

Confirmation of HBeAg seroconversion. 

90 days

HBs Ab (Anti-HBs / Hepatitis B Surface Antibody)  

1. HBsAg non reactive

2. Monitoring of immunization (after complete 3 doses of vaccine)

3. New HCW screening. 

4. Immunosuppression cases (eg. B-thal, ESRF, chemotherapy etc)

5. Needle stick injury (staff)

• Hepatitis B surface antibody with titre >10mIU/ml : No repeat necessary.

• Titre <10mIU/ml: 30 days

• Thalassemia/regular blood transfusion and hemodialysis : 180 days. 

HBs Ab (Anti-HBs / Hepatitis B Surface Antibody)  

1. HBsAg non reactive

2. Monitoring of immunization (after complete 3 doses of vaccine)

3. New HCW screening. 

4. Immunosuppression cases (eg. B-thal, ESRF, chemotherapy etc)

5. Needle stick injury (staff)

• Hepatitis B surface antibody with titre >10mIU/ml : No repeat necessary.

• Titre <10mIU/ml: 30 days

• Thalassemia/regular blood transfusion and hemodialysis : 180 days. 

HBs Ag (Hepatitis B Surface Antigen) 

1. High risk behaviour

(eg. IV drug user, MSM, multiple sexual partner, STI, partner with STI)

2. Person needing immunosuppressive therapy

(eg. chemotherapy, organ transplantation, immunosuppression for rheumatologic and gastroenterologic disorder)

3. Transaminitis of unknown aetiology

4. Haemodialysis patient

5. Donors of blood, plasma, organs, tissues or semen

6. All pregnant mothers

7. Infants born to HBsAg-positive mothers (send after 9 months old)

8. Household, needle-sharing, or sex contacts of persons known to be HBsAg positive

9. Persons who are the sources of blood or body fluids resulting in an exposure (eg. needlestick injury, sexual assault) that might require postexposure prophylaxis.

10. HIV-positive person

11. Healthcare worker

90 days

If reactive, repeat after 6 months to assess chronicity

If Non reactive :repeat after 90 days based on risk, clinical indication, sign and symptoms.

*Depending on clinical indications, earlier retesting may be necessary. Please consult with a Clinical Microbiologist for further discussion on early testing..

Anti-HCV (Hepatitis C Virus Antibody) 

1. High risk behaviour

(eg. IV drug user, MSM, multiple sexual partner, STI, partner with STI)

2. Person needing immunosuppressive therapy

(eg. chemotherapy, organ transplantation, immunosuppression for rheumatologic and gastroenterologic disorder)

3. Transaminitis of unknown aetiology

4. Haemodialysis patient

5. Donors of blood, plasma, organs, tissues or semen

6. Household, needle-sharing, or sex contacts of persons known to be HBsAg positive

7. Persons who are the sources of blood or body fluids resulting in an exposure (eg. needlestick injury, sexual assault) that might require postexposure prophylaxis.

8. HIV-positive person

9. Healthcare worker screening

90 days

If reactive, Anti HCV will be present life long thus repeat Anti-HCV is not indicated. 

HSV 1 & 2 IgM/IgG (Herpes Simplex Virus 

1. Immunocompromised patients

2. Transplant patients 

3. Diagnosis of Genital Herpes/ Oral Herpes

90 days

Toxoplasma IgG / IgM 

1. Congenital toxoplasmosis: chorioretinitis, intracranial calcification, hydrocephalus

2. Immunocompromised individuals (eg. HIV, transplant recipients)

3. Uveitis

4. Brain Space occupying lesion

14 days

Rubella IgG / IgM  

1. Congenital Rubella Syndrome (CRS): low birth weight, microcephaly, cataracts, sensorineural hearing loss, congenital heart disease, hepatosplenomegaly, purpura, intellectual disability

2. Postnatal: maculopapular rash with fever, malaise and lymphadenopathy 

14 days

If Rubella IgG reactive, repeat testing is not indicated. 

Rubella IgM may be repeated if negative in 14 days to diagnose acute infection. 

CMV IgG / IgM (Cytomegalovirus) 

1. Congenital CMV infection: microcephaly, IUGR, rash, jaundice, chorioretinitis, hepatosplenomegaly, hearing loss, intellectual disability)

2. Premature <30 weeks, very low birth weight <1500g

3. Immunocompromised patient: HIV (retinitis, encephalitis), pre- & post-transplant 

90 days

CMV IgG is not indicated to repeat once reactive as it may persist for life

VZV IgG/IgM (Varicella Zoster Virus) 

1. Chicken pox

2. Shingles 

90 days

Once reactive, VZV IgG remains detectable lifelong; therefore, repeat VZV IgG testing is not indicated. 

EBV IgM (Epstein-Barr Virus IgM) 

EBV IgG (Epstein-Barr Virus IgG) 

1. Infectious mononucleosis: Fever, malaise, headache, tonsillitis/pharyngitis, tender cervical lymphadenopathy

2. Lymphoma

3. Lymphadenopathy

4. Hepatitis

90 days

Once reactive, EBV IgG remains detectable lifelong; therefore, repeat EBV IgG testing is not indicated. 

EBV IgM (Epstein-Barr Virus IgM) 

EBV IgG (Epstein-Barr Virus IgG) 

1. Infectious mononucleosis: Fever, malaise, headache, tonsillitis/pharyngitis, tender cervical lymphadenopathy

2. Lymphoma

3. Lymphadenopathy

4. Hepatitis

90 days

EBV IgG is not indicated to repeat once reactive as it may persist for life

Dengue ELISA IgM/IgG 

1. Lives in or recent travel to dengue prone area

2.  Clinically dengue fever or TRO dengue (fever + arthralgia/myalgia, rash, warning sign-abd pain, vomiting, bleeding, lethargy) 

5 days (if negative)

No repeat testing required if initial test is positive. 

HIV RNA Viral Load

Monitoring response to ART

Baseline assessment in newly diagnosed HIV

Detection of treatment failure or resistance

90 days

Yearly if Viral load already suppressed. 

HBV DNA Viral Load

Monitoring response to antiviral

Baseline assessment in newly diagnosed hepatitis B

Detection of treatment failure or resistance

180 days

HCV RNA Viral load

Monitoring response to antiviral

Confirmation of Hepatitis C if Anti-HCV is reactive

90 days

Patient on treatment: 12 weeks and 24 weeks to confirm Sustained Virologic Response (SVR)

ASOT (Anti- Streptolysin O Titer) 

1. Streptococcus group A related diseases (heart, joints, skin, brain)

2. Erythema nodosum

3. Scarlet fever

4. Rheumatic fever

5. Post infectious glomerulonephritis

14  days

Retesting may be done 2–4 weeks after initial testing to assess the rise in titers if the clinical symptoms suggest a recent streptococcal infection. 

Mycoplasma (Mycoplasma pneumoniae) 

Used to diagnose infections caused by Mycoplasma pneumoniae, such as atypical pneumonia and other respiratory infections.

14 days

Routine repeat testing is not needed once a clear positive or negative result is obtained 

VDRL

Screening test for syphilis. It detects non-specific antibodies (reagin) associated with syphilis infection, especially in early stages.

3-6 months

Retesting in 3–6 months in individuals with risk factors or if symptoms persist despite treatment. Follow-up testing may also be done in pregnancy or after treatment to ensure resolution 

RPR (Rapid Plasma Reagin) 

Screening test for syphilis, similar to VDRL. It detects reagin antibodies and is used to assess the presence of syphilis, especially in the early and latent stages. 

3-6 months

Retesting is done 6 months after treatment for syphilis to ensure treatment effectiveness or during pregnancy to monitor potential congenital syphilis.

Anti-Nuclear Antibody (ANA) 

1. Connective tissue disease screening eg: SLE(92%)

2. Nephrotic syndrome

3. Eye neuropathy

4. Prolonged fever for investigation

5. Interstitial lung disease

If negative, allow repeat 24 months

If positive, no repeat test required.

Anti-dsDNA (Anti-double-stranded DNA) 

Positive ANA 

Diagnosis and monitoring disease activity in SLE. 

90 days.

Retesting indicated when there is clinical suspicion of flare. 

Routine repeat testing is not necessary if disease is quiescent. 

Extractable Nuclear Antibodies (ENA) 

Positive ANA 

To look for specific antibodies in ANA positive sample. 

180 days

Once positive, repeat testing is not indicated. 

Retesting is indicated only for equivocal results (2–4 weeks) or if new autoimmune overlap is clinically suspected. Routine monitoring by ENA panel is not recommended

Anti-Cyclic Citrullinated Peptides (Anti-CCP) 

1. Rheumatoid arthritis

2. RF positive (allow for confirmation of rheumatoid arthritis - more specific)

90 days

Anti‑CCP is highly specific for RA. Once positive, it remains detectable long‑term. Repeat testing is not required for diagnostic confirmation.

Cytoplasmic ANCA (c-ANCA) 

Perinuclear-ANCA (p-ANCA) 

1. Cutaneous vasculitis

2. Glomerulonephritis

3. Pulmonary hemorrhage (pulmonary renal syndrome)/lung nodule

4. Chronic destructive disease of upper airways

5. Long standing sinusitis or otitis

6. Subglottic tracheal stenosis, mononeuritis multiplex

7. Peripheral neuropathy

8. Retro-orbital mass

9. Scleritis 

10. Unexplained systemic vasculitis

11. Rapidly progressive glomerulonephritis (RPGN)

12. Pulmonary infiltrates with hemoptysis.

13. Asthma with eosinophilia and systemic features

14. Unexplained constitutional symptoms

30 days

Once positive, ANCA antibodies may persist for years.Routine repeat testing is not recommended. 

Anti-Mitochondrial Antibody (AMA)

Anti-Smooth Muscle Antibody (ASMA)

Anti-Liver Kidney Microsomal Antibody (Anti-LKM)

1. TRO autoimmune liver disease (however Hep B/C non reactive or reactive)

2. Primary biliary cholangitis (PBC)

3. Primary sclerosing cholangitis (PSC)

4. Mixed form (PBC/AIH)

180 days 

Once positive, usually persist lifelong.Routine repeat testing is not indicated, as positivity does not fluctuate meaningfully with disease activity.

Retesting is only justified if there is a significant change in clinical status (e.g., suspected autoimmune hepatitis flare, new cholestatic features).

Anti-Cardiolipin Antibody (ACL) 

Anti-Beta 2 Glycoprotein-1 (Anti-β2GP1) 

1. >3 unexplained miscarriage <10 weeks gestation

2. Unprovoked arterial or venous thrombosis with no risk factor

3. Unexplained fetal death >10 weeks gestation

4. Plan to stop medication for unprovoked DVT/PE

5. Premature birth with normal morphology <35 weeks gestation due to severe pre-eclampsia or IUGR

90 days 

Minimum 12 weeks. 

Ear Swab Culture & Sensitivity

1. Suspected otitis externa (pain, discharge, itching)

2. Chronic suppurative otitis media (persistent ear discharge)

3. Recurrent or non-resolving ear infections

4. Post-surgical ear infections

7 Days

Throat swab

1.     Suspected bacterial pharyngitis (e.g., Group A Streptococcus)

2.     Tonsillitis

3.   Diphtheria suspicion 

Negative swab : 3 days

Eye Swab For Culture and Sensitivity

1. Suspected bacterial conjunctivitis

2. Keratitis or severe eye infections

3.    Non-resolving or recurrent eye infections 

7 days

Genital Swab for Culture and Sensitivity

1.     Suspected sexually transmitted infections (STIs)

2.     Abnormal discharge

3.   Pelvic inflammatory disease (PID) 

14 days if symptoms remain after treatment.

Pus Swab For Culture and Sensitivity

1.     Infected wounds (redness, swelling, pus)

2.     Abscesses requiring drainage

3.     Diabetic foot infections

4.   Post-surgical infections 

3 days or once per episode of drainage 

Sputum for culture (this excludes investigation of TB) 

1.     Suspected bacterial/fungal pneumonia

2.   Chronic lung infections (e.g., bronchiectasis) 

3 days

Urine Culture and Sensitivity 

1.     Symptoms of urinary tract infection (UTI): dysuria, frequency, urgency

2.     Pyelonephritis (fever + flank pain)

3.     Recurrent or complicated UTI

4.     Screening in pregnancy

5.   Before urological procedures 

3 days

Stool For Culture and Sensitivity

1.     Acute diarrhoea with blood or mucus/fever/severe dehydration

2.     Suspected bacterial gastroenteritis (e.g., outbreak)

3.    Immunocompromised patients 

7 days

Acid Fast Bacilli (AFB) Direct Smear

1. Suspected Pulmonary Tuberculosis

2. Monitoring activity in Known TB Cases

3. Evaluation of treatment response

4. Screening in high risk group. 

24 hours. 

For screening: 2 samples, include one early morning sputum.

Urine TB Lipoarabinomannan (TB-LAM) / Urine TB Antigen TesT

1. HIV-positive patients with advanced immunosuppression (CD4 <200 cells/µL)

Not recommended for routine repeat unless initial specimen is invalid. 

MTB RIF Detection (Rapid molecular detection)

1. Suspected Pulmonary Tuberculosis

2. Detection of Rifampicin resistance

3. Extrapulmonary TB diagnosis

4. Smear Negative PTB

Not recommended for routine repeat unless initial specimen is invalid.