OK, my computer is glitching, I'm going to try AGAIN! And advance warning - this is a LONG post!
You need to do a do-it-yourself course in the immune system and how it works, in order to REALLY understand what is going on and to REALLY know how to save time and energy (and often a lot of money) in this process. There is a lot or rubbish out there masquerading as science - you need to evaluate it in context so if you decide to check it all out anyway, you know exactly where it all fits in.
An absolutely brilliant book - "The Body at War" by John Dwyer. It may be out of print but libraries should still have it somewhere. I know a later edition came out in about 1990, US & Australian release. He's an Aussie who also spent a lot of time working in the US as a pediatrician and immunologist, before moving to Sydney to practice. He has retired from clinical practice but is still heavily involved in teaching and research. He's a darn good teacher (and the book reflects this) having the rare gift of being able to explain complex things in an easy to understand (and interesting) way. I've attended a number of his lecture to lay people, most came out knowing more about immunology than the average GP.
The immune system is complex - just about anything involving the bloodstream and circulation is complex. But complex like a diesel engine - with a good manual you can get a really thorough understanding of it.
In your bloodstream you have red cells and white cells. The red cells carry oxygen and waste products; the white cells form a major part of the defence system - the immune system. There are other parts too, I'm being very simplistic here, but it's the basic stuff.
Your white cells include (among other things) two major groups - B cells and T cells. You've heard about T cells - they're the ones attacked by HIV - the AIDS virus. And this is bad, because it's the T cells which recognise invading organisms and trigger the body to begin the attack, and to also build defences against any future attack (by giving instructions for making antibodies). Killing off T cells, as HIV does, is why AIDS is so nasty when it really gets a grip - defence system is shot to pieces.
But the B cells - they respond to foreign substances, and respond fast. They are designed to trigger an inflammatory response, which then is supposed to set other things in train to help the body eject a foreign substance. B cells work a different way - they set off mast cells, which are little more than bags of histamine. Wherever a mast cell explodes, you get a small localised inflammatory response. This is what causes hives. And this is the only TRUE allergy - when you get wither hives, or anaphylaxis. Because both of these are histamine reactions. We treat allergies with anti-histamines, designed to cool down the B-cell response.
A B-cell response is fast. Depending on how it is delivered, it is usually within minutes, sometimes seconds. I heard of one girl with an allergy to horse serum (back in the days when it was used) who broke open an ampoule for the doctor and collapsed immediately - a sliver of glass from the ampoule had punctured her glove and gone under her fingernail. The doctor immediately guess what had happened and saved her, but some reactions are that fast.
Allergy tests - these are limited. Sorry. The ones you had done on your son are the most accurate. These are testing for that immediate reaction, the fast mast cell effect. And these, if there are any positive results, are the ones where you have to carry an Epipen.
A negative result doesn't mean no allergy, only that any allergy tested for isn't as nasty (at this time) as it could be.
The test itself - two ways of doing it. One way involved the immunologist sitting there with a lot of different vials, each one testing a specific series of allergens you were concerned about. The doctor has a box of tiny bottles, he puts a tiny drop on the skin and then with a sterile lancet, scratches the skin through the drop. It's time consuming and expensive. By the time the doctor has done the series, the first scratches should be ready to read. I have had this done where I was asked to wait for half an hour though. When I had it done, he wrote on my arm with a felt pen which had to be washed off - I think he used a permanent marker. It washed off later with a sterile swab.
The second way is to use a pre-packaged block. This is becoming increasingly common, especially since these blocks were manufactured and marketed. They are cheaper to use, faster to use and frankly, more accurate. The block has about sixteen heads on it, each one has a 'foot' which terminates in a circle of small plastic spines, each one loaded with a specific antigen. The most time consuming part is where the person doing the test has to peel off the seal on each foot of the block. They then press the block onto a cleaned patch of skin and wait.
Among the test antigens on this block, you will find two controls - a positive and a negative. The positive is a histamine test. The negative is sterile water. You SHOULD react to the histamine (which would give a typical response you would find if an allergy showed up on one of the other test sites) and you SHOULD NOT react to the water. If your reaction is faulty with these two, the entire test is suspect and you are about to get investigated, big time!
So in your son - at least one of those lumps is a histamine control. it is possible there were two histamine controls. If so, they probably would have been either next to each other, or at opposite ends of the test block - there is no need to randomise position in the block, your skin doesn't care whether you know or not. But by all means, ring and ask, for the sake of your peace of mind.
Often a positive to an allergy will show up as much more positive than the histamine reaction. Because an allergy is your body's immune system, designed to protect you, going overboard and trying to crack a walnut with nuclear weapons.
Now, to other tests - the same plastic block (at least, one similar in appearance but maybe loaded with different antigens) can also be used for what is called a DTH or delayed hypersensitivity test. It's not really of value in testing specific allergies (or sensitivities) as much as how your immune system in general is 'set' - sensitive, or sluggish. I've had a lot of DTH tests done over the years and although I know I'm allergic to a few things they test, I don't get a huge reaction, only a normal one, AND it is delayed. For me in the DTH, it was always the number of positives I got (the test was read at two days) which told the doctors more about my immune system - definitely overactive.
Back to allergy tests and now results - I told you I've had scratch tests done, looking for the B-cell reaction (the fast one). I tested negative, even though I had already had allergic reactions (with urticaria) to penicillin, erythromycin and sulfa. None of these three showed up and I remember at the time thinking they were incompetent for not sticking around to see if they reacted later (one of them did). But the doctor explained to me - the histamine positive had come up and the water hadn't, which meant the testing had been done properly. But my failure to react on my skin didn't mean I wasn't allergic; it just meant that my allergy, at that time, was not going to be immediately life-threatening. I didn't need to carry an Epipen (which didn't exist back then anyway). This is always subject to change, however, as your body gets increasingly sensitised.
Other types of allergy tests - these are very much open to debate. The blood tests are championed by some and considered quackery by others. The accuracy is a huge issue - how to you test for something when it's locked away in how your blood reacts while it is in your body? It is less likely to react that way when it's in a test tube. Because the blood test can't look for antibodies - that's T-cell, not B-cell. And this sort of blood test - very expensive, because it is so very meticulous.
Maybe it's the Gen-Y thing, but we keep looking to medical science to give us the instant answers. "Probe my body and tell me exactly what is wrong." And medicine cannot. Not always, especially not when it's a matter of such fine detail. I mentioned the immune system as being like a diesel engine - the scratch tests are like doing a diagnostic on the engine while it is running - it will tell you a great deal about that specific area. The blood tests are like analysing the engine oil of the machine and trying to use that to determine if the idle is too fast. OK, there MIGHT be a bit more carbon in the oil perhaps...
You are afraid for your son because you have seen him develop allergic reaction or some other sensitivity reaction. The tests are limited, but YOU can do other tests, especially if you have a good immunologist advising you. Those tests include keeping good records and trusting your own powers of observation.
I know I am allergic to certain antibiotics because when I take them, I get a rash. I've never had anaphylaxis (and don't want to, ever). I know I am sensitive to other medications because when I take them I get very ill in ways not associated with mast cells or histamine - I vomit, or get some other problem which means I cannot take that medication.
Because I have made these observations and kept records about them, I can keep myself safe from doctors prescribing something which could be dangerous for me. My mother in law is sensitive (not allergic) to morphine, but this did not prevent medical staff from giving her pethidine after open heart surgery. The extreme vomiting which resulted made her desperately ill with cardiac inflammation and kept her in hospital for 8 weeks, when she should have been out of hospital in three days. Although it was not an allergic reaction but a sensitivity one, it still almost killed her just the same. She now wears an SOS Talisman medalert medallion round her neck. So do I.
All these reactions are important to note, but very few can be empirically tested for.
It still comes down to your own parenting, your own observation and trusting yourself to be accurate in your reporting of your child's medical history.
I probably haven't explained things too well - get the book I recommended out of the library. It is much better at explaining this, probably less boring, too.
Marg