title: Concentration of lymph node aspirate improves the sensitivity of acid fast smear microscopy for the diagnosis of tuberculous lymphadenitis in Jimma, southwest Ethiopia.
abstract: BACKGROUND
  Tuberculous lymphadenitis (TBLN) is the most common form of extrapulmonary tuberculosis. The cytomorphological features of lymph node smears have reduced specificity for the diagnosis of tuberculosis. The diagnosis of TBLN with direct smear microscopy lacks sensitivity due to the limited number of bacilli in lymph node aspirate. Therefore, we aimed to assess whether the concentration of lymph node aspirate improves the sensitivity of acid fast smear microscopy for the diagnosis of tuberculous lymphadenitis.
  
  
  METHODS
  A cross-sectional comparative study was conducted on 200 patients clinically suspected for tuberculous lymphadenitis in Jimma, Ethiopia. Lymph node aspirate was collected. The first two drops were used for cytomorphological study and direct acid fast staining. The remaining aspirate was treated with N-acetyl-L-cysteine (NALC) and concentrated by centrifugation at 3000 g for 15 minutes. The sediment was used for acid fast staining and culture. Differentiation of M. tuberculosis complex (MTBC) from non-tuberculous mycobacteria (NTM) was done by para-nitrobenzoic acid susceptibility test.
  
  
  RESULTS
  Complete data were available for 187 study subjects. 68% (127/187) were positive for M. tuberculosis on culture. Four isolates, 2.1% (4/187), were identified as NTM. The detection rate of direct smear microscopy was 25.1% and that of the concentration method 49.7%. Cytomorphologically, 79.7% of cases were classified as TBLN. The sensitivity of direct smear microscopy was 34.6%, for concentrated smear microscopy 66.1%, and for cytomorphology 89.8%. Two AFB positive cases on concentration method were non-tuberculosis mycobacteria (NTM). The concentration method yielded a positive result from seven cases diagnosed as suppurative abscess by cytology. Both for the direct and concentration methods the highest rate of AFB positivity was observed in smears showing caseous necrosis alone. Smear positivity rate decreased with the appearance of epithelioid cell aggregates.
  
  
  CONCLUSIONS
  The concentration of lymph node aspirates for acid fast smear microscopy had significantly higher sensitivity than direct microscopy.
authors.affiliation: Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Mulualem
authors.initials: M
authors.lastname: Tadesse
authors.affiliation: Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Gemeda
authors.initials: G
authors.lastname: Abebe
authors.affiliation: Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Ketema
authors.initials: K
authors.lastname: Abdissa
authors.affiliation: Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Alemayehu
authors.initials: A
authors.lastname: Bekele
authors.affiliation: Department of Medical Laboratory Sciences and Pathology, Jimma University, Jimma, Ethiopia.
authors.forename: Mesele
authors.initials: M
authors.lastname: Bezabih
authors.affiliation: Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Apers
authors.affiliation: Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Epidemiology and Social Medicine, University of Antwerp, Antwerp, Belgium.
authors.forename: Robert
authors.initials: R
authors.lastname: Colebunders
authors.affiliation: Mycobacteriology Unit, Department of Microbiology, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Rigouts
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry; D000293:Adolescent; D000328:Adult; D000368:Aged; D001707:Biopsy, Needle / Q000379:methods; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005002:Ethiopia / Q000453:epidemiology; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000382:microbiology / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis; D009579:Nitrobenzoates / Q000737:chemistry; D014388:Tuberculosis, Lymph Node / Q000453:epidemiology / Q000473:pathology*
chemical_list: D009579:Nitrobenzoates; D000111:Acetylcysteine