Investing.com -- Company insiders in the life science and diagnostic tools sector sold $187 million worth of stock during the first quarter of 2026, according to a Barclays analysis released Tuesday.

The analysis covered 20 companies and found that only five saw net insider purchases during the quarter. Avantor Inc (NYSE: AVTR), Waters Corp (NYSE: WAT), Illumina Inc (NASDAQ: ILMN), Quest Diagnostics Inc (NYSE: DGX), and Charles River Laboratories International Inc (NYSE: CRL) were the only companies where insiders bought shares in the open market.

Avantor led open market purchases with approximately $2.4 million in insider buying, representing about 0.04% of shares outstanding. This marked the fourth consecutive quarter of insider buying at Avantor, with insiders purchasing roughly $11.2 million of stock since the second quarter of 2025.

The remaining purchases at Waters, Illumina, Quest Diagnostics, and Charles River were relatively small, each representing less than 0.01% of shares outstanding.

On the selling side, Medpace Holdings Inc (NASDAQ: MEDP) saw the largest open market insider sales at approximately $14 million, or about 32,000 shares, representing 0.11% of shares outstanding. Guardant Health Inc (NASDAQ: GH) followed with roughly $6 million in sales, or about 63,000 shares.

Twist Bioscience Corp (NASDAQ: TWST) insiders sold approximately $5 million worth of stock, or 100,000 shares, representing about 0.17% of shares outstanding.

Natera Inc (NASDAQ: NTRA) insiders executed the most pre-scheduled sales, selling approximately $123 million worth of stock, or 568,000 shares, nearly all of which were pre-scheduled transactions.

Overall, insiders purchased $2.9 million worth of stock in the open market during the first quarter, compared to $33 million in total open market sales.