Calprotectin is a soluble protein that is found in white cells; it is part of the bodies defence mechanism and has strong antibacterial and antifungal properties through its ability to sequester metal ions. Calprotectin is actually formed from two proteins, S100-A8 and S100-A9 (alternatively known as MRP-8 and MRP-9) and it is the heterodimer of these two proteins that is found inside the white cells. When calprotectin is released from white cells, it initiates a strong inflammatory response and rapidly forms a tetrameric format in conjunction with metal ions (calcium, zinc, magnesium).
There is as much calprotectin in white cells as there is haemoglobin in red cells accounting for around 60% of the soluble protein content. In conditions which provoke an inflammatory response the level of calprotectin in the blood can increase significantly and although it is a non-specific marker, it can be used to aide diagnosis and determine the severity of certain conditions in conjunction with the other clinical evidence. The diagnostic advantage of calprotectin detection over other disease markers is that it is stored in the cell and released immediately in response to local situations. In contrast, other markers may be released by downstream pathways or need to be synthesised leading to delays in detection.
Although calprotectin is a non-specific marker, there have been publications to show it to be of value in the diagnosis and monitoring of various conditions including:
Rheumatoid and juvenile idiopathic arthritis
An early marker for sepsis
An early marker for acute coronary syndromes
Idiopathic pulmonary fibrosis
Behcet’s disease
Stills disease
Systemic lupus erythematosus
Systemic sclerosis
Primary Sjorgens Syndrome
EULAR/PReS Recommends Serum Calprotectin for Diagnosing Still’s Disease
The taskforce of the EULAR/PReS has recommended the use of serum calprotectin for the diagnosis of Still’s disease. This is a very clear statement that serum calprotectin plays a crucial role in the pathophysiology of autoinflammatory rheumatic diseases like Still’s disease.
The taskforce has officially agreed that the previous two distinct diseases systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still’s disease (AOSD) are actually the same disease, to be known as Still’s disease.
Annals of Rheumatic Diseases EULAR/PReS recommendations for the diagnosis and management of Still’s disease, comprising systemic juvenile idiopathic arthritis and adult-onset Still’s disease “Marked elevation of serum IL-18 and/or S100 proteins (eg, calprotectin) strongly supports the diagnosis [of Still’s disease], and therefore should be measured if available.” https://ard.bmj.com/content/early/2024/10/15/ard-2024-225851
sCAL turbo
The BÜHLMANN sCAL® turbo is an in vitro diagnostic test designed for the quantitative determination of the tetrameric format of calprotectin (MRP8/14) in human serum samples to avoid the background calprotectin that will be found in standard blood samples. This is the dominant format found in serum due to the high and even distribution of calcium.
The BÜHLMANN sCAL® turbo test is a particle enhanced turbidimetric immunoassay (PETIA) and allows quantification of calprotectin in human serum samples on clinical chemistry analysers. Samples can be measured without any additional dilution steps and are incubated with reaction buffer and mixed with polystyrene nanoparticles coated with calprotectin-specific antibodies (immunoparticles). Any calprotectin available in the sample mediates immunoparticle agglutination and sample turbidity which is measured by light absorbance. The detected light absorbance allows quantification of calprotectin concentration via interpolation on an established calibration curve.
Assay Details
Sample volume: ~2-3µl
Time to first result: 10 minutes
Assay Range: 0.23 – 15µg/ml but can dilute 1:15 to cover 15 – 225µg/ml
Number of tests: Approximately 100 (dependent on the platform used)
All reagents are ready to use and have an on-board stability of 55 days
Calibration is stable for at least 30 days, but is analyser dependant
Accuracy/Recovery: 92 – 112.8%
Limit of Detection: 0.11µg/ml
Limit of Quantification: 0.23µg/ml
There is excellent correlation to other turbidimetric assays that are available:
Assay standardisation:
The BÜHLMANN sCAL® turbo is standardized against internal reference material (purified native calprotectin). Calibrator and control values are assigned according to a value transfer protocol (ref. 1, 2), to guarantee metrological traceability. The analytical measuring interval of the BÜHLMANN sCAL® turbo, established on the Mindray BS-480 instrument, is 0.23-15.0 μg/mL.
Sample Collection:
Blood can be collected into a serum tube or a gel separator tube, once clotted the tubes are centrifuged at 1800g for 15 minutes and then the serum transferred into a plain tube. This then prevents the contamination of the sample with un-released calprotectin which would cause higher values. Once separated the samples can be stored at 2-8C for 16 days or for 1 month at -20C.
Reference Interval:
The reference interval of the BÜHLMANN sCAL® turbo assay was established according to CLSI C28-A3 with 160 serum samples from self-declared healthy individuals: adult men and women aged 18 to 83 years. The samples were collected either in native tube or tube with gel separator and processed within 3-4 hours after collection.
Comparison of the BUHLMANN sCAL ELISA to the sCAL turbo:
Because the assays are manufactured by the same company they have a good correlation, however they are based on different standardisations and so will give significantly different results. The sCAL ELISA is based on the historic use of the dimeric format which will include the background level found normally within blood.
The sCAL turbo is based on the tetrameric format which avoids the background level and so lower values will be obtained.
References
A novel Serum Calprotectin (MRP8/14) particle enhanced immuno-turbidimetric assay (sCAL turbo) helps to differentiate SJIA from other diseases in routine clinical laboratory settings
The sCAL turbo assay showed an excellent correlation to the MRP8/14 ELISA used in the previous validation studies (r=0.99, p<0.001). It could reliably differentiate SJIA from all other diagnoses with significant accuracy (cut-off at 9,100 ng/ml, sensitivity 93%, specificity 87%, ROC area under curve 0.961 p<0.001).
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