Increased natural killer cell activity (NKCA) is linked to reduced risk of colorectal cancer (CRC). Several prior studies have investigated the association of NKCA and the incidence of CRC in high-risk subjects. The aim of our study was to investigate NKCA sensitivity in diagnosing advanced neoplasia (AN) and CRC in an average risk population.

Material and methods:
NKCA was assessed by an enzyme-linked immunosorbent assay (ELISA) blood test in average risk subjects with a range of 25–2500 pg/ml set for ELISA. NKCA higher than 200 pg/ml was defined as negative. The performance of NKCA was evaluated using measures such as sensitivity, specificity, negative and positive predictive values (NPV, PPV), clinical utility index, etc. In addition, odds ratios for developing CRC using logistic regression models were calculated.

NKCA was evaluated in 354 average risk individuals (mean age: 58.5 years; 36.2% male). The diagnostic accuracy of NKCA for CRC and AN was 75.5% and 72.3% respectively, with 96.4% NPV. The NKCA test demonstrated a good negative clinical utility index for CRC and AN (0.664 and 0.741, respectively). Individuals with low NKCA had 6.84 times higher odds of having CRC (95% CI: 2.31–20.27; p < 0.001). NKCA was higher in men vs. women (548.5 pg/ml vs. 500.0 pg/ml) and lower in smokers (412 pg/ml vs. 544 pg/ml), non-exercisers (413 pg/ml vs. 653.5 pg/ml), alcohol users (389 pg/ml vs. 476 pg/ml), and native Kazakhs and other Asian ethnic groups (446 pg/ml vs. 514 pg/ml).

A high NKCA level has potential ability to rule out CRC and AN in an average risk population.