(Reuters) - Medical device maker Dexcom ( DXCM ) cut its annual revenue forecast on Thursday, blaming a restructuring of its sales team, fewer customers, and lower revenue from each customer, sending its shares plummeting 40% in extended trading.

The company expects 2024 revenue of about $4 billion to $4.05 billion, compared with its previous forecast of $4.20 billion to $4.35 billion. Analysts on an average were expecting $4.33 billion, according to LSEG data.

Dexcom ( DXCM ) makes continuous glucose monitors (CGM) - wearable devices that track glucose levels throughout the day without the need for fingerstick blood tests. It has been facing competition from Abbott and Medtronic ( MDT ).

Revenue from Dexcom's ( DXCM ) US customers dipped quicker than was expected, as customers took advantage of rebates for the new CGM called G7, CEO Kevin Sayer said on a post-earnings call with analysts.

The company also forecast third-quarter revenue of about $975 million to $1 billion, below estimates of $1.15 billion.

It reported second-quarter revenue of $1 billion, compared with estimates of $1.03 billion.