Cryoglobulins Dx

Synonyms:  Cryo’s, Cryofibrinogen

CPT-Code:  82595

Definition: Cryoglobulins are immunoglobulins that reversibly precipitate in the cold (4°C). The reversibility of precipitation by warming the sample to body temperature (37°C) distinguishes cryoglobulins from other cold-precipitable proteins such as cryofibrinogen.

Classification: Cryoglobulins are usually classified into one of three categories, depending on the characteristics of their component immunoglobulins (Table).

• Type I:  includes monoclonal antibodies, which can be of any of the major immunoglobulin classes (IgA, IgG, IgM). Such monoclonal proteins may be produced by malignant clonal expansion of B lymphocytes. Monoclonal cryoglobulins are commonly seen in multiple myeloma and Waldenström‘s macroglobulinemia (see Cryoglobulinemia).
• Type II:  mixed cryoglobulins are common and refers to both monoclonal and polyclonal antibodies being present. The most common mixed cryoglobulin consists of a monoclonal IgM with RF activity that binds polyclonal IgG. Such complexes are associated with idiopathic mixed cryoglobulinemia, hepatitis C, Sjögren’s syndrome, and lymphoproliferative disorders.
• Type III:  cryoglobulins that do not contain any monoclonal components and are most commonly associated with connective tissue diseases such as RA and SLE.  Type III cryoglobulins are usually present in low concentrations, often with cryocrits <1%.

Method (Collection of Sample): Serum samples to be processed for detection of cryoglobulins must be collected carefully to ensure accurate quantitation. Samples cannot be collected during routine scheduled phlebotomy. The laboratory that is to receive the sample must be notified in advance to prepare for processing. Because some cryoprecipitation may occur even at room temperature (22°C), collection must be in a Vacutainer tube prewarmed to 37°C in a portable water bath. The bath can be fashioned from a small covered Styrofoam box or jug with an indwelling thermometer. Blood is drawn into the prewarmed tube, which is then placed in the warm water bath for immediate transport to the laboratory. Samples may be rejected if the specimen has cooled to <36°C. Once received, the blood is allowed to clot completely at 37°C. This procedure is designed to keep all cryoprecipitable proteins in the serum rather than in the blood clot. The clotted sample is spun in a warm centrifuge, and serum is removed and stored at 4°C. Samples are usually kept in the cold for 72 hours to allow precise quantitation, although cryoprecipitate accumulation can often be detected visually after 24 hours. The volume of cryoprecipitate is quantitated in a tube similar to a hematocrit tube, and results are expressed as a percentage of the serum volume. High levels may reach values of >10%; levels <1% are difficult to quantitate accurately. Alternatively, the precipitate can be centrifuged out of the cold serum, washed, and resuspended in warm buffer. The amount of protein is then determined spectrophotometrically, and values are expressed as milligrams per total volume of serum.

Typing: After quantitation, cryoprecipitate components may be characterized by counterimmunoelectrophoresis. Specific antibodies are used to detect heavy chains identifying the major immunoglobulin classes as well as the accompanying light chains. Expression of exclusively A or K light chains by an immunoglobulin in the precipitate indicates monoclonality. Detection of RF positivity within the cryoprecipitate (tested under warmed conditions) is often useful in characterization.

Normal Values: Values are usually negative (cryocrit, <1%; serum, <80 f.Lg/mL).

Clinical Associations: Cryoglobulins are found in a wide variety of disorders, including infection (e.g., infective endocarditis, hepatitis, Epstein-Barr virus, syphilis), autoimmune disorders (e.g., SLE, RA, polyarteritis nodosa, Sjögren’s syndrome, scleroderma, Kawasaki’s disease), lymphoproliferative disorders (e.g., multiple myeloma, lymphoma, Waldenström’s macroglobulinemia), and hyperviscosity syndrome, or it may be idiopathic (essential mixed cryoglobulinemia).

The most clinically important syndromes associated with cryoglobulins are nephritis and cutaneous vasculitis. Essential mixed cryoglobulinemia may demonstrate an acute glomerulonephritis, and patients with this syndrome should be screened for the presence of cryoglobulins in serum. Cryoproteins present a unique appearance in renal biopsies and are usually recognized without special staining. Cutaneous vasculitis with palpable purpura, especially in the lower extremities, should suggest cryoglobulinemia. Biopsy of the rash commonly demonstrates leukocytoclastic vasculitis. Recently, associations of hepatitis C virus infection with type II mixed cryoglobulins have been reported, and this viral infection may represent a significant number of cases previously considered to be idiopathic or essential.

Indications: Cryoglobulin testing should be considered in patients suspected of cryoglobulinemia (i.e., palpable purpura, systemic illness) or those with no known cause for acute glomerulonephritis, severe Raynaud’s phenomenon, cutaneous vasculitis, or hyperviscosity syndrome.

Cost: $30–65.