Cytosorbents (CTSO)

Cytosorbents on one page: short interest, daily short volume, fails to deliver, large holders, 13F holders, earnings dates and insider trades. Listed on Nasdaq, classified by the SEC as surgical & medical instruments & apparatus.

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114K

Short interest

settlement 2026-10-15

10.3

Days to cover

-1.7 days vs prior

80.3%

Short share of volume

2026-11-03

755

Fails to deliver

settlement 2026-10-09

Thu 12 Nov

Next earnings

estimated date

$120K

Insider flow, 90 days

7 buys, 0 sells

As of 2026-11-03.

Short interest

FINRA, twice a month. The newest 48 settlements in the table, 48 in the chart. JSON

As of 15 October 2026, short interest in CTSO is 114,402 shares, down 6,204 shares over the last month. Over the last 48 readings it ranged from 114,402 shares (15 October 2026) to 2,306,196 shares (31 August 2026). The latest reading sits at the bottom of that range. At the reported average volume of 11K shares a day that is 10.3 days to cover.

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Settlement	Shares short	Change	Avg daily volume	Days to cover
2026-10-15	114,402	-7.7%	11,136	10.27
2026-09-30	123,890	+2.7%	10,339	11.98
2026-09-15	120,606	-94.8%	45,552	2.65
2026-08-31	2,306,196	+6.9%	126,008	18.30
2026-08-14	2,158,099	+0.7%	72,249	29.87
2026-07-31	2,142,523	+1.1%	55,888	38.34
2026-07-15	2,118,780	+1.9%	78,872	26.86
2026-06-30	2,078,902	-0.4%	333,438	6.23
2026-06-15	2,087,557	+0.8%	264,273	7.90
2026-05-29	2,071,713	+0.7%	111,887	18.52
2026-05-15	2,057,094	+0.7%	99,848	20.60
2026-04-30	2,042,494	-0.1%	43,286	47.19
2026-04-15	2,044,318	+1.2%	83,984	24.34
2026-03-31	2,020,680	+0.1%	134,521	15.02
2026-03-13	2,018,660	+0.9%	73,105	27.61
2026-02-27	2,000,812	-1.9%	51,125	39.14
2026-02-13	2,039,234	+0.1%	77,483	26.32
2026-01-30	2,036,463	+2.5%	78,920	25.80
2026-01-15	1,985,895	-0.8%	68,829	28.85
2025-12-31	2,002,634	+0.3%	151,262	13.24
2025-12-15	1,995,957	-0.9%	121,482	16.43
2025-11-28	2,013,299	+3.1%	124,043	16.23
2025-11-14	1,952,028	+24.6%	142,877	13.66
2025-10-31	1,566,174	+18.9%	79,185	19.78
2025-10-15	1,317,259	-1.9%	71,275	18.48
2025-09-30	1,342,026	-0.5%	86,404	15.53
2025-09-15	1,348,578	-2.8%	58,512	23.05
2025-08-29	1,387,175	-6.9%	186,080	7.45
2025-08-15	1,489,774	+8.9%	523,492	2.85
2025-07-31	1,367,365	-5.0%	68,334	20.01
2025-07-15	1,438,944	-2.9%	129,796	11.09
2025-06-30	1,481,862	+3.4%	141,449	10.48
2025-06-13	1,433,439	-2.1%	74,479	19.25
2025-05-30	1,463,783	-1.4%	93,721	15.62
2025-05-15	1,485,065	-1.3%	195,738	7.59
2025-04-30	1,505,054	-7.4%	68,498	21.97
2025-04-15	1,624,985	-6.9%	76,404	21.27
2025-03-31	1,745,606	-5.2%	70,779	24.66
2025-03-14	1,842,019	-0.4%	103,321	17.83
2025-02-28	1,850,036	-5.2%	126,245	14.65
2025-02-14	1,950,582	+0.8%	178,212	10.95
2025-01-31	1,934,385	+5.5%	80,276	24.10
2025-01-15	1,833,139	+26.6%	996,776	1.84
2024-12-31	1,447,610	+3.6%	177,629	8.15
2024-12-13	1,397,411	+2.0%	154,426	9.05
2024-11-29	1,369,474	+5.4%	103,615	13.22
2024-11-15	1,298,947	-4.2%	195,370	6.65
2024-10-31	1,355,760	+0.5%	97,074	13.97

Daily short volume

FINRA Reg SHO, the last 30 sessions. JSON

As of 3 November 2026, the short share of CTSO volume is 80.3%, up 49.1 points over the last five sessions. Over the last 30 readings it ranged from 6.4% (6 October 2026) to 81.6% (30 September 2026). The latest reading sits at the top of that range. The latest reading is 39.0 points above the 30-session average of 41.2%, on 5K shares reported.

Date	Short volume	Total volume	Short share	Exempt
2026-11-03	4K	5K	80.3%	166
2026-11-02	1K	10K	11.7%	20
2026-10-30	4K	14K	30.1%	1,456
2026-10-29	2K	22K	7.5%	59
2026-10-28	2K	6K	25.4%	0
2026-10-27	4K	13K	31.2%	1,696
2026-10-26	14K	22K	63.0%	2,608
2026-10-23	2K	22K	10.7%	32
2026-10-22	14K	42K	32.3%	0
2026-10-21	11K	24K	47.0%	0
2026-10-20	8K	29K	27.9%	0
2026-10-19	70K	135K	52.0%	798
2026-10-16	267K	381K	70.2%	1,332
2026-10-15	2K	8K	24.2%	948
2026-10-14	5K	11K	47.9%	673
2026-10-13	918	5K	20.1%	0
2026-10-12	2K	7K	36.4%	0
2026-10-09	1K	3K	33.6%	0
2026-10-08	3K	5K	56.5%	0
2026-10-07	810	3K	28.6%	0
2026-10-06	880	14K	6.4%	0
2026-10-05	2K	3K	53.1%	0
2026-10-02	3K	5K	76.6%	0
2026-10-01	2K	3K	46.2%	1
2026-09-30	6K	7K	81.6%	0
2026-09-29	2K	4K	49.0%	0
2026-09-28	1K	11K	10.7%	0
2026-09-25	1K	3K	48.2%	0
2026-09-24	12K	16K	71.5%	2,373
2026-09-23	2K	4K	57.5%	0

Fails to deliver

SEC, the last 30 settlement dates with a fail. JSON

As of 9 October 2026, the fails-to-deliver balance in CTSO is 755 shares, up 719 shares over the last settlement date. Over the last 30 readings it ranged from 1 share (29 July 2026) to 57,180 shares (15 June 2026). The latest reading sits at the bottom of that range.

Settlement	Shares failed	Price	Value
2026-10-09	755	$3.73	$3K
2026-10-08	36	$3.87	$139
2026-10-07	1,468	$3.96	$6K
2026-10-02	390	$4.05	$2K
2026-09-25	7	$4.35	$30
2026-09-24	185	$5.02	$929
2026-09-17	96	$5.73	$550
2026-09-16	65	$6.06	$394
2026-09-15	751	$5.75	$4K
2026-09-14	4,859	$6.41	$31K
2026-09-10	856	$6.33	$5K
2026-09-09	481	$6.76	$3K
2026-09-02	11	$0.34	$4
2026-09-01	1,646	$0.34	$560
2026-08-26	2,737	$0.36	$985
2026-08-14	3,929	$0.36	$1K
2026-07-29	1	$0.37	$0
2026-07-28	78	$0.36	$28
2026-07-23	7,838	$0.38	$3K
2026-07-02	20,709	$0.39	$8K
2026-06-23	82	$0.41	$34
2026-06-22	960	$0.44	$422
2026-06-15	57,180	$0.40	$23K
2026-06-12	30	$0.39	$12
2026-06-04	33,042	$0.49	$16K
2026-06-01	1,741	$0.49	$853
2026-05-29	3,909	$0.50	$2K
2026-05-28	913	$0.49	$447
2026-05-26	3,707	$0.46	$2K
2026-05-22	4,314	$0.46	$2K

Insider trades

SEC Form 4, newest first. JSON

Insiders at CTSO reported 7 open-market buys worth $120K in the last 90 days and no open-market sells. Latest filing: Sobel Alan D. (Director) on 2026-09-15.

Date	Insider	Title	Type	Shares	Price	Value	Owned after
2026-09-15	Sobel Alan D.	Director	Buy	100	$6.01	$601	10K
2026-09-15	Sobel Alan D.	Director	Buy	500	$6.05	$3K	10K
2026-09-15	Sobel Alan D.	Director	Buy	2K	$6.12	$12K	9K
2026-09-15	Chan Phillip P.	Chief Executive Officer	Buy	4K	$6.00	$23K	101K
2026-09-14	Capponi Vincent	President and COO	Buy	273	$5.90	$2K	40K
2026-09-14	Capponi Vincent	President and COO	Buy	2K	$6.07	$11K	40K
2026-09-04	Chan Phillip P.	Chief Executive Officer	Buy	200K	$0.35	$70K	1.9M
2026-06-15	Chan Phillip P.	Chief Executive Officer	Buy	10K	$0.43	$4K	1.7M
2026-06-15	MARIANI PETER J	Chief Financial Officer	Buy	100K	$0.44	$44K	638K
2026-06-12	Chan Phillip P.	Chief Executive Officer	Buy	251K	$0.40	$100K	1.7M
2025-11-18	Chan Phillip P.	Chief Executive Officer	Grant	100K	$0.64	$64K	1.5M
2025-08-08	MARIANI PETER J	Chief Financial Officer	Grant	72K	$0.00	$0	538K
2025-08-08	Deliargyris Efthymios	Chief Medical Officer	Grant	70K	$0.00	$0	473K
2025-08-08	Chan Phillip P.	Chief Executive Officer	Grant	106K	$0.00	$0	1.4M
2025-08-08	Capponi Vincent	President and COO	Grant	89K	$0.00	$0	766K
2025-02-24	Sobel Alan D.	Director	Exercise (out of the money)	22K	$1.13	$25K	146K
2025-02-24	Chan Phillip P.	Chief Executive Officer	Exercise (out of the money)	34K	$1.13	$39K	1.3M
2025-02-24	MARIANI PETER J	Chief Financial Officer	Exercise (out of the money)	33K	$1.13	$37K	467K
2025-02-24	Capponi Vincent	President and COO	Exercise (out of the money)	12K	$1.13	$14K	677K
2025-02-24	BATOR MICHAEL G.	Director	Exercise (out of the money)	10K	$1.13	$11K	151K
2025-01-17	MARIANI PETER J	Chief Financial Officer	Exercise (in or at the money)	33K	$1.00	$33K	434K
2025-01-17	Chan Phillip P.	Chief Executive Officer	Exercise (in or at the money)	91K	$1.00	$91K	1.2M
2025-01-17	Sobel Alan D.	Director	Exercise (in or at the money)	22K	$1.00	$22K	124K
2025-01-17	Deliargyris Efthymios	Chief Medical Officer	Exercise (in or at the money)	16K	$1.00	$16K	403K
2025-01-17	Capponi Vincent	President and COO	Exercise (in or at the money)	32K	$1.00	$32K	665K
2025-01-17	BATOR MICHAEL G.	Director	Exercise (in or at the money)	16K	$1.00	$16K	141K
2024-12-13	MARIANI PETER J	Chief Financial Officer	Buy	20K	$0.96	$19K	401K
2024-12-12	MARIANI PETER J	Chief Financial Officer	Buy	20K	$0.89	$18K	381K
2024-12-11	MARIANI PETER J	Chief Financial Officer	Buy	11K	$0.89	$10K	361K
2024-08-14	MARIANI PETER J	Chief Financial Officer	Grant	110K	$0.00	$0	110K
2024-08-14	MARIANI PETER J	Chief Financial Officer	Grant	65K	$0.00	$0	175K
2024-08-14	MARIANI PETER J	Chief Financial Officer	Grant	175K	$0.00	$0	350K
2024-04-02	Chan Phillip P.	Chief Executive Officer	Grant	96K	$0.00	$0	1.2M
2024-04-02	Capponi Vincent	President and COO	Grant	81K	$0.00	$0	665K
2024-04-02	BLOCH KATHLEEN P.	Chief Financial Officer	Grant	65K	$0.00	$0	533K
2024-04-02	Deliargyris Efthymios	Chief Medical Officer	Grant	61K	$0.00	$0	409K
2023-12-13	Chan Phillip P.	Chief Executive Officer	Buy	75K	$1.33	$100K	1.1M
2023-12-13	Kim Jiny	Director	Buy	8K	$1.33	$10K	78K
2023-12-13	BLOCH KATHLEEN P.	Chief Financial Officer	Buy	38K	$1.33	$50K	468K
2023-12-13	Jones Edward Raymond	Director	Buy	8K	$1.33	$10K	89K
2023-12-13	BATOR MICHAEL G.	Director	Buy	38K	$1.33	$50K	125K
2023-12-13	Capponi Vincent	President & COO	Buy	19K	$1.33	$25K	584K
2023-12-13	Deliargyris Efthymios	Chief Medical Officer	Buy	23K	$1.33	$30K	348K
2023-12-13	Sobel Alan D.	Director	Buy	23K	$1.33	$30K	102K
2023-09-18	BLOCH KATHLEEN P.	Chief Financial Officer	Grant	45K	$0.00	$0	442K
2023-08-07	BATOR MICHAEL G.	Director	Buy	1K	$3.20	$3K	87K
2023-08-07	BATOR MICHAEL G.	Director	Buy	1K	$3.15	$3K	88K
2023-08-04	BATOR MICHAEL G.	Director	Buy	1K	$3.23	$3K	86K
2023-07-07	Deliargyris Efthymios	Chief Medical Officer	Grant	55K	$0.00	$0	332K
2023-07-07	Capponi Vincent	President & COO	Grant	73K	$0.00	$0	576K
2023-07-07	Chan Phillip P.	Chief Executive Officer	Grant	87K	$0.00	$0	1.0M
2023-05-25	BLOCH KATHLEEN P.	Interim CFO	Buy	1K	$2.85	$3K	47K
2023-05-25	BLOCH KATHLEEN P.	Interim CFO	Buy	1K	$2.84	$3K	46K
2023-05-25	BLOCH KATHLEEN P.	Interim CFO	Buy	1K	$2.85	$3K	45K
2023-05-10	BLOCH KATHLEEN P.	Interim CFO	Buy	2K	$3.13	$6K	41K
2023-05-10	BLOCH KATHLEEN P.	Interim CFO	Buy	3K	$3.17	$10K	44K
2023-05-10	BLOCH KATHLEEN P.	Interim CFO	Buy	5K	$3.06	$15K	39K
2023-04-04	Capponi Vincent	See Remarks	Exercise or conversion	10K	$2.88	$29K	512K
2023-04-03	Chan Phillip P.	Chief Executive Officer	Exercise or conversion	31K	$2.88	$88K	928K
2023-02-27	Sobel Alan D.	Director	Gift	2K	$0.00	$0	81K
2023-02-27	Sobel Alan D.	Director	Gift	2K	$0.00	$0	0
2023-02-06	Kraus Al	Director	Exercise or conversion	12K	$2.65	$32K	142K
2022-12-08	Chan Phillip P.	Chief Executive Officer	Buy	6K	$1.26	$7K	897K
2022-12-07	Chan Phillip P.	Chief Executive Officer	Buy	10K	$1.26	$12K	891K
2022-12-06	Chan Phillip P.	Chief Executive Officer	Buy	14K	$1.26	$18K	882K
2022-09-08	Chan Phillip P.	Chief Executive Officer	Buy	35K	$1.70	$60K	867K
2022-08-25	Unknown	Director	Buy	1K	$1.91	$2K	70K
2022-08-10	Chan Phillip P.	Chief Executive Officer	Grant	79K	$0.00	$0	845K
2022-08-10	BLOCH KATHLEEN P.	Chief Financial Officer	Grant	56K	$0.00	$0	405K
2022-08-10	Capponi Vincent	President and COO	Grant	69K	$0.00	$0	513K
2022-08-10	Deliargyris Efthymios	Chief Medical Officer	Grant	55K	$0.00	$0	228K
2022-08-10	Deliargyris Efthymios	Chief Medical Officer	Grant	52K	$0.00	$0	283K
2022-06-21	Capponi Vincent	President and COO	Buy	2K	$1.80	$4K	444K
2022-06-16	Chan Phillip P.	Chief Executive Officer	Buy	2K	$1.85	$4K	768K
2022-06-16	Capponi Vincent	See Remarks	Buy	3K	$2.00	$6K	442K
2022-06-09	Chan Phillip P.	Chief Executive Officer	Buy	16K	$2.17	$35K	766K
2022-06-06	BLOCH KATHLEEN P.	Chief Financial Officer	Buy	9K	$1.90	$17K	34K
2022-05-23	Capponi Vincent	President and COO	Buy	299	$2.03	$607	435K
2022-05-23	Capponi Vincent	President and COO	Buy	2K	$2.04	$3K	435K
2022-05-23	Capponi Vincent	President and COO	Buy	3K	$2.03	$6K	439K
2022-05-18	BATOR MICHAEL G.	Director	Buy	2K	$2.20	$4K	84K
2022-05-18	BATOR MICHAEL G.	Director	Buy	2K	$2.20	$4K	80K
2022-05-18	BATOR MICHAEL G.	Director	Buy	2K	$2.18	$4K	78K
2022-05-18	BATOR MICHAEL G.	Director	Buy	2K	$2.18	$4K	76K
2022-05-18	BATOR MICHAEL G.	Director	Buy	2K	$2.20	$4K	82K
2022-05-18	BATOR MICHAEL G.	Director	Buy	1K	$2.21	$2K	85K
2022-05-16	Jones Edward Raymond	Director	Buy	2K	$2.24	$4K	81K
2022-05-11	Sobel Alan D.	Director	Buy	1K	$2.00	$2K	71K
2022-05-11	Sobel Alan D.	Director	Buy	9K	$2.02	$18K	79K
2022-05-06	Kraus Al	Director	Buy	5K	$1.96	$10K	130K
2022-04-05	Kim Jiny	Director	Grant	69K	$0.00	$0	69K
2022-02-14	Sobel Alan D.	Director	Gift	2K	$0.00	$0	2K
2021-12-30	Chan Phillip P.	Chief Executive Officer	Buy	5K	$4.05	$22K	768K
2021-12-29	Chan Phillip P.	Chief Executive Officer	Buy	9K	$4.05	$38K	763K
2021-12-29	Chan Phillip P.	Chief Executive Officer	Buy	100	$4.04	$404	754K
2021-12-10	Chan Phillip P.	Chief Executive Officer	Buy	5K	$5.25	$26K	753K
2021-12-09	Jones Edward Raymond	Director	Tax withholding	3K	$5.22	$17K	80K
2021-12-09	Jones Edward Raymond	Director	Exercise or conversion	4K	$4.13	$17K	83K
2021-11-23	BLOCH KATHLEEN P.	Chief Financial Officer	Buy	4K	$4.98	$20K	25K
2021-08-31	Kraus Al	Director	Sell	4K	$9.40	$38K	125K

Form 4 filings are due within two business days of the trade. Insiders sell for many reasons that say nothing about the company; open-market buys are rarer.

Large holders (13D and 13G)

One row per reporting person with its latest filing, newest first. JSON

2 holders report 5% or more of CTSO in their latest filing, all on Schedule 13G (passive). The largest reported stake is AVENIR CORP at 8.3% of the class (5,230,099 shares), filed 2026-02-13 for an event on 2025-12-31.

Filed	Form	Holder	Shares	Of class	Event
2026-02-13	13G/Ano. 4	AVENIR CORPinvestment adviser	5.2M	8.3%	2025-12-31
2026-02-13	13G/Ano. 4	James H. Rooneyindividual	n/a	8.3%	2025-12-31

13F holders

Tracked managers holding CTSO at their latest 13F. JSON

1 of the 30 tracked managers held CTSO at their latest 13F, $37K in total at quarter-end prices. Renaissance Technologies is the largest at $37K (0.0% of its portfolio) as of 2026-06-30. Over the prior quarter 0 added shares and 1 cut.

Fund	Quarter	Shares	Value	Of portfolio	Change in shares
Renaissance Technologies	2026-06-30	100K	$37K	0.00%	-700

Only the 30 tracked managers on the funds hub; a 13F reports long positions in US listed stock at quarter end, 45 days late, and says nothing about shorts or positions sold since.

What this page is

Cytosorbents in the regulatory record

Regulators publish company data in separate files that never sit next to each other: FINRA's twice-monthly short interest, its daily short sale volume, the SEC's fails-to-deliver counts, and each insider's Form 4. A company page puts those series for one ticker on one URL, with planned sales, large holders, 13F holders and financials beside them, so the short position, the daily flow, the settlement fails and what insiders are doing can be read together.

Each section has its own history table, a one-line summary of the latest figures and its own JSON and CSV links, and says when its source last updated.

This page follows Cytosorbents (CTSO), SEC CIK 1175151, listed on Nasdaq, classified by the SEC as surgical & medical instruments & apparatus. The cross-market tables live on the short interest and insider transactions hubs.

Source and updates

Short interest: FINRA consolidated short interestSource: FINRA.Twice a month, about eight business days after settlement. Latest 2026-10-15.JSON and CSV
Daily short volume: FINRA Reg SHO daily filesSource: FINRA.Every trading day, the morning after FINRA posts it. Latest 2026-11-03.JSON and CSV
Fails to deliver: SEC fails-to-deliver dataSource: SEC.Twice a month, a few weeks after the half month ends. Latest 2026-10-09.JSON and CSV
Large holders: SEC EDGAR Schedule 13D and 13GSource: SEC.New filings appear shortly after the SEC posts them. A 13D is due within five business days of crossing 5%; a 13G follows the passive schedule. Latest 2026-02-13.JSON and CSV
13F holders: SEC EDGAR Form 13F-HRSource: SEC.Quarterly, filed within 45 days of quarter end; 30 tracked managers. Latest 2026-06-30.JSON and CSV
Earnings dates: SEC EDGAR 8-K filings (Item 2.02)Source: SEC.Twice a day. Reported dates come from the company's 8-K filings; the next date is marked as an estimate until the 8-K arrives. Latest 2026-08-06.JSON and CSV
Insider trades: SEC EDGAR Form 4Source: SEC.New filings appear shortly after the SEC posts them; they're due two business days after the trade. Latest 2026-09-15.JSON and CSV
Company record: EDGAR filing index for CIK 1175151Ticker, name and exchange from the SEC's company list, refreshed weekly.
Rate limits: 10 requests a minute without a key, 30 with a free key from a free account.

How to read it

Read the position against the flow: rising short interest with a high daily short share is new shorting; rising short interest with a normal short share is old shorts holding on.
Insider buys next to a large short position are rare and stand out; insider sells next to one are common and mean little.
Fails to deliver matter relative to the float, not in absolute shares; a million failed shares in a mega cap is noise.

Analysis of what the data shows, not advice. XOOMAR does not recommend buying, selling or holding anything.

Other companies the SEC classifies as surgical & medical instruments & apparatus

Other company pages

Datasets

Frequently Asked Questions

How much of CTSO is sold short?

114,402 shares were held short at the 2026-10-15 settlement, 10.3 days of average volume. FINRA publishes the next count about eight business days after the 15th and the last business day of the month.

What is CTSO's daily short volume?

On 2026-11-03, 4,273 of the 5,323 CTSO shares reported to FINRA were sold short, 80.3% of the day's reported volume. Short volume is a flow for one day, not a position.

Does CTSO have fails to deliver?

The SEC's latest file shows 755 CTSO shares failed to deliver at settlement 2026-10-09. Fails are reported per settlement date and published twice a month with a lag.

Are CTSO insiders buying or selling?

Insiders at CTSO reported 7 open-market buys worth $120K in the last 90 days and no open-market sells. Latest filing: Sobel Alan D. (Director) on 2026-09-15.

Who owns 5% or more of CTSO?

Which tracked 13F managers own CTSO?

1 of the 30 tracked 13F managers held CTSO shares at their latest filing, $37K in all. The largest: Renaissance Technologies (100K shares, $37K).

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