Qualitative vs Quantitative testing for Cryoglobulins
The qualitative test for cryoglobulins is a test for the presence of cryoglobulins only. It gives no indication of the level or type of cryoglobulins found. The quantitative test for cryoglobulins returns the type and level of cryoglobulins present.
A single qualitative positive test for cryoglobulins qualifies as a diagnosis for cryoglobulinemia. Some doctors like to use the quantitative cryocrit test to measure the level of cryoglobulins as a diagnositic indicator.
The level of cryoglobulins in the blood are NOT good indicators for the severity or diagnosis of cryoglobulinemia.
It is well known that the cryoglobulin levels are highly variable from one patient to the next, and in any individual patient can fluctuate greatly, and may actually be absent altogether at times. Furthermore, while many labs make claims of accuracy, the accuracy of cryocrit measurements has never been well established, and a “standard” level for cryoglobulins as a diagnostic does not exist.
The bottom line is , one patient might have 3% cryoglobulins in their blood and be extremely ill with cryoglobulinemia, and yet another patient might have 11% cryoglobulins, and be completely asymptomatic. We don’t know why. . Every now and then one encounters a doctor who insists that cryoglobulin levels must be greater than 11% for a diagnosis of cryoglbulinemia. This is completely wrong, and arbitrary, and is simply not supported by the facts. Cryoglobulinemia is defined as the presence of cryoglobulins in the blood. Because of this clear and simple definition, the mere presence of cryoglobulins is taken as the diagnostic indicator for cryoglobulinemia. If you have cryoglobulins, regardless of the level, you have cryoglobulinemia, by definition.
Some doctors like to have a second positive for cryogobulins to confirm the diagnosis. This approach is likely not workable most of the time unless you can find a facility that does the test themselves, does it correctly, does it reliably, and you don’t mind repeating the test *A LOT*. This is because the test for cryoglobulins is not done correctly by most labs, and a false negative is returned about 70-75% of the time, At the same time false positives are uncommon.
In very real terms, one positive in the face of symptoms for cryo is compelling, and this is where most doctors will make the call, and call it cryoglobulinemia. The hard part is finding what is causing the cryo…
NOTE: putting heparin in the test tube is another way to get a false positive if the tech does not know how to tell fibrin deposits from cryoglobulins.
A second positive cryo test is something to try for, but is sometimes not possible or practical to obtain. I’ve had ONE positive qualitative test, and have been tested for quantitative cryoglobulins about 6 times. The trouble is that the only time I was tested for cryoglobulins when I was flaring, and I clearly observed that the specimen was collected and handled correctly, was the single qualitative positive. On one other occasion blood was drawn correctly and the sample was then placed in a thermos for mailing to an outside lab for a quantitative test… but at that time I was in remission and we were trying to make sure I was in remission before changing the meds…. of course it came back negative. Other attempts at getting a cryoglobulin test were clearly done incorrectly from the beginning with the blood simply being drawn, the test-tube placed in a rack and the sample shipped to an outside lab. The lab doing the test in most cases was LabCorp. My first positive was taken at Washington Adventist hospital, and it was drawn and handled carefully by a head nurse,, not just a phlebotomist. My most recent test was done at the University of Maryland Medical Center, and I had requested a test for cryogobulins while there. At no time was a blood specimen drawn and handled with regard to temperature. The hospital records reported a negative test result, but I’m not even sure the test was actually performed.