CSL shares were down 16.9 per cent on Monday afternoon to $99.65, their lowest level since December 2016, reducing the company's market capitalisation from $57 billion on Friday to $46 billion.
The plunge came after the biopharmaceutical firm said it was writing off $US5 billion ($6.9 billion) from the value of its Vifor kidney treatment business, which CSL acquired in 2021 for 10.9 billion Swiss francs ($19.4 billion).
The company also downgraded its earnings guidance, expecting to make a full-year profit of $US3.1 billion on $US15.2 billion of revenue, figures down four per cent and two per cent from 2024/25, respectively.
The company had previously predicted revenue and profit growth.
"At the first-half results, we called out ambitious growth expectations for IG (immunoglobulin), China albumin and our launch products," CSL chief financial officer Ken Lim told analysts.
"Regrettably, those ambitions have not been fully realised."
There was excess immunoglobulin in the US, China's market for the blood protein albumin continued to decline by value and the Middle East conflict had meant a pause in sales to Iran, Mr Lim said.
Meanwhile, cheaper generic versions of a Vifor-manufactured injection used to treat iron-deficiency anaemia launched in the US in late 2025, leading CSL to further write down the value of that division on top of a $US843 impairment declared in February.
It has been a tough few years for CSL, whose shares are down 42.5 per cent in 2026 after a 38.7 per cent drop in 2025.
Former chief executive and managing director Paul McKenzie retired abruptly in February after an internal review found he didn't have the skills to take the company forward.
Gordon Naylor, a non-executive director of the company, was appointed interim chief executive and launched a 90-day review that culminated in Monday's announcement.
A comprehensive review of its balance sheet found it was clear CSL's $32 billion in invested capital was not working as hard as it should, Mr Naylor said.
As the company's asset base has grown, its return on invested capital has fallen, he said.
For example, CSL has been slow to respond to the gains of its competitors in the plasma industry in the US, where it has fallen to be the third-largest immunoglobulin player by volume, Mr Naylor said.
The company has also under-utilised property, plant and equipment, the company said.
Mr Naylor said CSL was working to turn things around.
"There is no fundamental shift in business strategy," he said.
"This is primarily about excellence in execution."
A global search for a new chief executive is ongoing, but Mr Naylor said he would not be among the candidates for the job.
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