[Amoebic Liver Abscess][Dr. O.P. Kapoor]
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ROLE OF SEROLOGICAL TESTS

. The diagnosis of amoebic liver abscess remains a difficult task since most of the liver function tests give non-specific results in this condition. Liver scan only shows a cold area, the etiology of which cannot usually be predicted. Serologic study is especially useful in evaluation of such patients. The development of new techniques in serology holds some promise for the clinicians in this situation.1
Unfortunately the early methods fell into disrepute largely due to the non-specificity of the antigen which could not be separated from bacterial contaminants With the advent of anexic cultivation of E. Histolytica,2 improved soluble antigens have been made and more reproducible and standardized tests have resulted.
The following are the various serological tests3 described for the diagnosis of amoebiasis:
  1. Gel diffusion precipitation test.
  2. Indirect haemagglutintion test (I.H.A. test)
  3. Complement fixation test.
  4. Fluorescent antibody test.
  5. Latex agglutinaion test (L A test).
  6. Bentonite flocculation and bentonite phagocytosis test.
  7. Immunoelectrophoresis
  8. Skin test.

The fist three tests are perhaps the best known although they are relatively laborious.
Among the various serologic tests employed-agar gel diffusion, indirect haemagglutination, indirect immunofluorescence and countercurrent immunoelectrophoresis are the most useful for the diagnosis of amoebic liver abscess. The indirect haemagglutination O.H.A.) test is very sensitive.4 I.H.A. titres of 1:128 and above are considered to be positive for diagnosis of amoebiasis. However, as mentioned earlier (Section II), only high titres are diagnostic of amoebic liver abscess. The positivity of the test compares with immunofluorescence and gives a maimum positive response upto 95S in cases of amoebic liver abscess.'5 Recent investigators 6,7 using l.H.A. tests have recorded from 87 to 100% positive reboes in cases of liver abscess. In one hundred cases of amoebiasis in whom l.H.A. test was done by Kumar8 she noted, that in thirty cases of amoebic liver abscess, the test was positive in a titre of more than 1:512.
I have experience with I.H.A. test only. According to my observations l.H.A. test is valuable in diagnosis of amoebic liver abscess, only if it is positive in high dilutions (preferably more than 1:1024). Most of my patients showed a titre of 1:2048 or more. I have seen fake positives (even as high as 1:2048 in one case of viral hepatitis) quite often, especially in a titre of 1:128.
More significant is my experience of seeing two patients with negative I.H.A. test. Unfortunately, one of the patients was a diagnostic problem, because of massive GI bleed per rectum. Routine plain X-ray of abdomen fortunately showed typical signs of a massive superior surface amoebic liver abscess with pleural involvement. Aspiration showed typical brownish pus and the bleed was from colonic ulcers. This case is discussed elsewhere (Section Vl).
In clinical practice, on the whole, I.H.A. test is more useful if it is negative (in excluding amoebic liver abscess). If it is positive in very high dilutions diagnosis of amoebic liver abscess is much more likely. After cure, I.H.A. test may remain positive for three years or more.9
A simple latex agglutination test is now available as a commercial kit 10 It is only a moderately sensitive test It can be done in less than 30 minutes. Although a positive L.A. test in a case of suspected amoebic liver abscess is not diagnostic, it can lead a clinician to start specific treament, until other tests are completed. L.A. test is positive in 84% cases of amoebic liver abscess.1 However, as it is a simple procedure and may be performed rapidly, it may be used as a screening test for invasive amoebiasis.5 The chief drawback of the test is the large percentage of positives in asymptomatic patients (with a range of 0 to 15% depending on exposure of the population).
Reports of indirect immunofluorescence technique (IF) quite often cannot be obtained within 24 hours. Instead countercurrent immunoelectrophoresis (C.l.E.) is a good, sensitive and specific screening procedure for rapid sero-diagnosis of critically ill patients suffering from amoebic liver abscess.11 In one series C.l.E. was 95% positive as compared to l.H.A. which was 90% positive in amoebic liver abscess. The respective false positivity was 1.7% and 6.7%.9
Thus, the diagnostic value of serological tests for amoebic liver abscess has been amply substantiated. Nevertheless, most of the available tests are too complicated for routine use in rural places.12 In the opinion of DeBakey and Jordan, 13 none of the serological tests are uniformly positive in all patients. False positives may occur. In their series, I.H.A. and gel diffusion precipitin tests have been reported to have accuracy in the range of 96%.
The skin test is a simple procedure. Development of a wheal of significant diameter was found in 92% of patients of amoebic liver abscess by Savanat et at. 12 Madangopalan3 found 70% positive response in amoebic liver abscess. However, skin test is more valuable in epidemiological studies.
Skin reactivity takes longer to develop after onset of clinical symptoms but once it has developed, it is more persistent than serum precipitating antibodies.
Mahajan et al14 found precipitating antibodies in amoebic liver pus. But the titres were lower than in serum as detected by C.l.E. These authors have also described the detection of amoebic antigen in the liver pus aspirate and found that it provided a very useful adjunct for rapid and specific diagnosis of amoebic liver abscess in most cases15
The recent development in perfection of technique for axenic cultivation of E. Histolytica at various centres in India will soon help in the manufacture of serodiagnostic aids in our country and make them easily available at low cost.
Krogstad et al 16 anticipate that within the next few years application of the enzyme linked immunosorbent assay (ELISA) technique will add greater sensitivity to detection of E. Histolytica antibody in serum, as well as the aspirates from liver abscess.

References

  1. Monroe, L. S., Korn, E R. et al, Am. J. Gastroent., 1972, 58, 52.
  2. Diamond, L S, J. Parasitol., 1968, 54, 1047.
  3. Madangopalan, N. Progress in Clinical Medicine in India, Arnold-Heinemann, India 1976.
  4. Healy, G R. Bull., N Y Acad. Med. 1971, 47, 478.
  5. Mahajan, R C, Ganguly, N K, et al, Ind. J Med. Res., 1972, 60, 372.
  6. Healy, G R. Health Lab. Sci., 1968, 5, 174.
  7. Milgram, E A, Healy, G R. et al, Gastroent, 1966, 50, 645.
  8. Kumar Sujata - Personal communication
  9. Bockus Henry, L, Gastroenterology, Vol. IV, 3rd Edition, W B Saunders & Co., Philad., 1976.
  10. Morris, et al, as quoted by Bockus, 1976.
  11. Mahajan, R C, Ganguly, N K, et al, Ind. I. Med. Res., 1975, 63, 54.
  12. Savanat, T. Burnag, D, et al, Am. J. Trop. Med. Hyg., 1973, 22, 168.
  13. DeBakey, M E, and Jordan, G L, Surg. Clin. N. Am, 1977, 57, 325.
  14. Mahajan, R C, Ganguly, N K, et al, Ind. J. Med. Res., 1975, 63, 229.
  15. Mahajan, R C, Ganguly, N K, et al, Lancet, 1976, 1, 651.
  16. Krogstad D J, Spencer, H C, et al, New Eng J. Med, 1978, 298, 262