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AFTER THE BLOOD TEST’S REPORT ASK YOURSELF A QUESTION -
“WHICH” METHOD WAS USED?
OP Kapoor
Ex. Hon. Physician, Jaslok Hospital and Bombay Hospital, Mumbai, Ex. Hon. Prof. of Medicine, Grant Medical College and JJ Hospital, Mumbai 400 008.
Day-by-day we are becoming dependent on the blood test’s reports. It is high time that the practitioner should learn as to how these tests are carried out. I will quote a few examples:-
1. Routine blood count : I would any day prefer the report of this test when it is done manually preferably by a good pathologist who is a good morphologist and spends time on seeing the smears. Most of the pathologists have started using histogram to save their time and energy and get readymade results from the machines. Most of the graphs drawn in the histograms and the RDW, PDW, MPV etc. do not give any information which is useful to a GP. The only advantage I can see is that the reading of platelet count is also “supplied” which may be useful in the diagnosis of malaria. I have seen on many occasions abnormal lymphocytes of infectious mono-nucleosis being missed. I have also seen leukaemic cells being missed on histogram report. MPs will not be reported on histogram.
2. Widal test is an agglutination test and therefore highly misguiding and a poor test and the readings are absolutely unreliable.
3. Blood cultures and sputum cultures : If the method used is by bactac, the report comes much earlier and quicker.
4. The interpretation of “Rheumatoid” factor is reliable only if the test is done by Nephilometry.
5. Elisa test - Many times when the tests are done by Elisa method the readings are wrong because there is no standard marker since multiple manufacturers make the kit. Thus ANA test and many other tests done by Elisa can be wrong. Tests carried out by indirect immuno-assay or chemino luminiscence are much more reliable.
6. ESR done by Wintrobe method is often wrong.
7. In a molecular laboratory where the PCRs are being done, although, the PCR done for HIV virus, HCV, HBV viruses are very reliable, PCR for AFB is often false positive.
8. All the tests showing antibodies are less reliable for diagnosis (specially IgG) while the demonstration of Antigen (Ag) is more reliable where we are talking about bacteria like Salmonella or protozoa like malaria or fungus like aspergillosis.
Family physicians should also remember the causes of false positive tests and the cross reactivity which can cause misinterpretation.
Finally, even big laboratories who save money on daily calibrations in the morning before starting and avoid doing double blind check, can give gross misguiding and wrong results of the blood tests.
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