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Cytokeratin 19 fragment in blood
Medical expert of the article
Last reviewed: 05.07.2025
Reference values (norm) of the concentration of cytokeratin fragment 19 (CYFRA-21-1) in blood serum are up to 3.3 ng/ml.
Cytokeratins are insoluble framework proteins. Unlike cytokeratins, cytokeratin fragments are soluble in blood serum. Cytokeratins play an important role in tissue differentiation. CYFRA-21-1 has good specificity for benign lung diseases, the cutoff point of 3.3 ng/ml provides 95% specificity. A slight increase in CYFRA-21-1 to 10 ng/ml is found in progressive benign liver diseases and especially in renal failure.
CYFRA-21-1 is a marker of non-small cell lung carcinoma. With a specificity of 95%, CYFRA-21-1 has a significantly higher sensitivity (49%) than CEA (29%). The sensitivity of CYFRA-21-1 for squamous cell lung carcinoma is significantly higher (60%) than the sensitivity of CEA (18%). CYFRA-21-1 and CEA exhibit similar diagnostic sensitivity (42% and 40%, respectively) for lung adenocarcinoma. The combination of these two markers increases the sensitivity to 55%.
CYFRA-21-1 is the most informative of all known markers for monitoring muscle-invasive bladder carcinoma. With a specificity of 95%, CYFRA-21-1 has a sensitivity of 56% for invasive tumors of all stages. The sensitivity of CYFRA-21-1 depends on the stage of the disease: 4% at stage I, more than 33% at stage II, 36% at stage III, up to 73% at stage IV bladder cancer.
More than 50% of bladder tumors do not infiltrate the muscular layer. They are easily detected during urological examination. Invasive tumors are more difficult to diagnose. Monitoring the CYFRA-21-1 marker in many cases allows us to identify such forms of bladder carcinomas.
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