Nothing wrong in this, because he can't ask everyone coming to him to take blood test at the very first sitting, then, no one will visit him back saying he sucks out blood all the time! But, it is okay to have a blood test after a week, but, not after a month! Diagnosing a disease after it had reached a severe stage is comparatively less significant than diagnosing at an early stage. So, how to diagnose?
Antigen - Antibody!Antigen and Antibody interactions are mainly used for diagnosing most of the diseases. When you give your blood sample to your doctor, he gives it to his lab, there they check for the presence of particular antigen in your blood. For example, if you have typhoid, surface proteins of the causative organism (Salmonella typhi) will act as antigen and when antibody (specific protein produced by your body against the antigen) is added to the infected blood sample antibody - antigen interaction occurs, which could be detected by various techniques.
Possible methods for diagnosing a disease!
There are several methods available for diagnosing a disease, but, most of them are based on the antigen-antibody interaction. Here I had listed a few methods of diagnosis, which I know:
1) ELISA - Enzyme Linked Immunosorbent Assay!
This method is based on the antigen antibody interaction. Two antibodies are used for detecting the presence of a single antigen. But, both the antibodies won't be directly reacting with the antigen, one antibody (primary) will be reacting with the antigen, and other antibody(secondary -which was raised against the primary antibody) will react further with the primary antibody used, producing color based on the enzyme linked with it. Generally done using 96 wells plate.
2) Western Blot!
This is also done for finding the presence of a specific protein (in diagnosis, the protein is antigen) in a given sample.This is done generally after doing SDS PAGE and transferring the protein separated in the gel to nitrocellulose membrane followed by similar technique of adding primary and secondary antibody, which will show color if there is infection.
3) PCR - Polymerase Chain Reaction
Though the presence of a particular gene could be detected using Southern blot, the most sensitive technique used for diagnosing a disease based on genes is PCR. Quantitative PCR could be done for even finding the severity of the disease based on the concentration of a particular gene of the causative organism.
I prefer to go with PCR than any other technique, but, when there is no thermo cycler in your laboratory it's better to go with ELISA! There are also other techniques like latex agglutination and microscopic observation of samples, but, the best way is PCR!
What do you say? PCR?