Grand Rounds

Positive Interferon-gamma Release Assay Result in a Child less than Two Years of Age: How to Interpret?

Dhruv Gandhi, Ira Shah
Department of Pediatric Infectious Diseases, BJ Wadia Hospital for Children, Mumbai, India

Address for Correspondence: Dhruv Gandhi, 5B/13 Shyam Niwas, Breach Candy, Mumbai-400026, Maharashtra, India. Email: dhruvgandhi2610@gmail.com

Keywords: IGRA, Mantoux test, Tuberculin skin test, Pediatric tuberculosis, Antitubercular therapy, Latent tuberculosis

Clinical Problem:
A 6-month-old boy presented in July 2024 with a right knee swelling and an inability to extend the right knee for 2.5 months. The swelling developed 10 days after receiving the Pentavalent vaccine in the right thigh. There was no history of fever, weight loss or loss of appetite. There is no history of tuberculosis (TB) contact. The patient had taken one month of oral cefaclor prior to presentation and did not report any improvement in the swelling size. On presentation, his weight was 7.2 kg (between 15th and 25th percentile according to the World Health Organisation (WHO) growth charts). On examination, a right knee fixed flexion deformity of 20 degrees was found. The range of knee flexion beyond 20 degrees was full and was painful up to 140 degrees of motion. The range of motion of both hips was normal. Magnetic resonance imaging (MRI) of the right knee showed mild effusion, moderate synovial thickening, irregularity of the articular surface of the unossified lateral femoral condyle and enlarged popliteal lymph nodes (7 x 6 mm). Ultrasound of both hips was normal. Other investigations are shown in Table 1. Ocular examination was normal. Synovial biopsy was advised but was not done. The patient was advised naproxen syrup and asked to follow-up after 4 weeks. At the 4-week follow-up, there was a decrease in the size of the swelling clinically and ultrasound showed a mild effusion with internal echoes and extension into the suprapatellar recess. The 3-tube Interferon-gamma release assay (IGRA) sent in August 2024 at an outside centre was positive with a titre of 1.39 IU/ml. Chest X-ray was normal. Naproxen was stopped and the patient was advised a repeat right knee ultrasound after 2 weeks. After 2 weeks, the right knee ultrasound showed no evidence of synovial effusion or thickening. The patient was not started on antitubercular treatment and was instead asked to follow-up after 2 months with a right knee ultrasound and IGRA testing. The follow-up ultrasound showed no joint effusion or thickening. IGRA was not done. The patient was advised to follow-up every three months with a right knee ultrasound.

Table 1. Investigations of the patient.

Parameters	Patient’s Values	Reference Range
Hemoglobin (gm/dL)	9.1	11.5-15.5
TLC (cells/cumm)	7950	5000-13,000
ANC (cells/cumm)	1638	2000-8000
ALC (cells/cumm)	5780	1000-5000
Platelets (106 cells/cumm)	4.52	1.50-4.50
ESR (mm/hr)	47	<15
CRP (mg/dL)	1	<1

Note: TLC- Total leukocyte count, ANC- Absolute neutrophil count, ALC- Absolute lymphocyte count, ESR-Erythrocyte sedimentation rate, CRP- C-reactive protein.

How to interpret IGRA results in a child less than 2 years of age?