What is SAA?

Serum Amyloid A is a non-specific acute phase time-phase response protein synthesised in the liver by activated macrophages and fibroblasts.It can rapidly activate and induce chemokines, which further stimulate the migration of monocytes, neutrophils, mast cells and T lymphocytes and act as a pro-inflammatory factor to accelerate the inflammatory response of the body.The clinical value of SAA as an inflammatory marker has gained widespread attention and is of great significance in the early diagnosis, efficacy assessment and prognostic evaluation of infectious diseases.

SAA changes significantly before and after the inflammatory response, the transcript level of the gene can be increased up to 200-fold during the inflammatory response, it can be significantly increased as soon as 4 hours after infection, it has a short half-life and a low basal concentration, and the mechanism of in vivo elimination of SAA is non-kidney-dependent.

SAA is widely used in the auxiliary diagnosis of infectious diseases, the prediction of coronary heart disease risk, the dynamic observation of the efficacy and prognosis of oncology patients, the observation of transplantation rejection, and the observation of the improvement of rheumatoid arthritis.

Clinical application of SAA

The application value of SAA in early diagnosis, risk assessment, efficacy observation and prognosis evaluation of infectious diseases has been generally recognised. Elevated levels of SAA have been detected in the serum of patients with non-infectious diseases such as type II diabetes mellitus, atherosclerosis, tumours, rheumatoid arthritis, transplant rejection, amyloidosis and so on, which is of guiding significance for the auxiliary diagnosis of the diseases.

During the acute phase of inflammation or infection, it rapidly increases in 48~72 hours and rapidly decreases in the recovery phase of the disease, so it is a sensitive marker of the inflammatory response.

Specific clinical applications of SAA are shown below:

① Early diagnosis of viral infections：SAA, an acute phase response protein, is significantly elevated to 10-100 mg/L during the acute phase of infections with a variety of viruses, such as influenza virus, respiratory syncytial virus, adenovirus and enterovirus.

② Early diagnosis of bacterial infections：SAA are more sensitive than CRP in early infection, rising earlier and falling faster and more dramatically on recovery.

③ Assessment of severity, prognosis and outcome of infectious diseases: SAA is a sensitive indicator of acute inflammation, the magnitude of which is largely dependent on the severity of the infection, and can be used as an independent factor in assessing the severity of infectious disease and inflammation.

④ SAA can be used as an independent risk factor for cardiovascular disease and its level can be used to assess the progression of the disease, which facilitates the early diagnosis, prevention and treatment of cardiovascular disease.

⑤ SAA can be used as a non-specific tumour marker for adjuvant diagnosis, therapeutic detection and prognosis of tumours.

⑥ SAA concentration can be used as a preferred indicator for rejection monitoring, facilitating early anti-rejection therapy and reducing the risk of graft failure.

Factors affecting SAA

Although elevated SAA concentrations are mainly from the occurrence of infectious diseases, there are also some non-infectious diseases that lead to elevated SAA levels, so we need to understand why SAA occurs, and the specific causes of SAA are as follows:

Infectious Disease

(Infection of the organism by pathogens such as bacteria, viruses, fungi, etc.)

Atherosclerosis

(Slow blood flow in the body, accompanied by chest tightness, headache and other discomforts)

Rheumatoid Arthritis

(Presence of rheumatoid factor in the body, accompanied by symptoms such as morning stiffness, swelling and pain in the joints)

Malignant Tumour

(When a malignant tumour metastasises, the tumour cells infiltrate and put the body under stress)

Septicaemia, Sepsis, Tuberculosis

Summary

SAA is a non-specific inflammatory marker with high sensitivity, short half-life and other characteristics, and has important reference value in the diagnosis and differential diagnosis of acute inflammation, follow-up of therapeutic efficacy and prognosis judgement.Although a number of non-specific inflammatory markers have been associated with cardiovascular disease, SAA is considered to be a better indicator of disease activity due to its wider dynamic range and more rapid response.

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References

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[2] Clinical Diagnosis and Experimental Medicine Branch of Chinese Maternal and Child Health Association. Expert consensus on the application of SAA alone and in combination with CRP in infectious diseases in children[J]. Laboratory medicine,2021,36(7):685-690. DOI:10.3969/j.issn.1673-8640.2021.07.001.

[3] CHEN Changqiang. Research progress of serum amyloid A in disease applications[J]. Laboratory medicine,2012,27(9):776-779. DOI:10.3969/j.issn.1673-8640.2012.09.020.

[4] Xingcheng Zhu, Yong Duan, Dongju Wang, et al. .PCT Clinical application value of hs-CRP and SAA detection in early diagnosis of sepsis[J]. Journal of Practical Laboratory Physicians,2014,6(1):27-30. DOI:10.3969/j.issn.1674-7151.2014.01.007.