CPT code 11900: Lesion injection, up to seven lesions2026 Medicare rate & RVUs in Iowa
Reports medication injected directly into one to seven skin lesions, such as keloids or hypertrophic scars, during a single treatment session.
In Iowa, Medicare pays $52.54 for 11900 in the office and $22.59 when it’s performed in a hospital or facility.
Check a contract rate as a % of Medicare · 11900 nationwide
Medicare allowed amount for participating (non-QP) physicians, before deductible, coinsurance and claim adjustments. Not a patient’s bill or a hospital charge.
On this page 11 sections
What 11900 covers
A clinician injects medication directly into skin lesions, commonly using an intralesional corticosteroid for keloids, hypertrophic scars, or selected inflammatory lesions. Dermatologists and other clinicians who treat these conditions perform the service in office settings and, less often, in facility settings. The code is selected by the number of lesions treated, not the number of needle passes or the medication volume; it covers treatment of one through seven lesions. More than seven lesions are reported with 11901.
Document the treated lesions and their number, the medication and dose, and the clinical reason for injection. The medication may be reported separately when applicable and supported by documentation. CMS assigns a 0-day global period, so same-day preoperative and postoperative care is included. When multiple procedures are performed in the same session, the highest-valued procedure is paid in full and others at 50%. Modifier 50 is inappropriate. Assistant-at-surgery payment is restricted, and co-surgeon and team-surgery reporting are not permitted.
This summary was written with AI assistance from CMS physician fee schedule data and checked against the CMS billing rules shown here. Rates on this page come directly from CMS files.
How Iowa compares for 11900
Across 109 of 109 payment localities, the office rate for 11900 runs from $50.60 in Arkansas to $74.71 in San Benito County, CA. Iowa pays $52.54. The RVUs are the same everywhere; the geographic indexes change the dollars.
- Iowa · this page$52.54
- Los Angeles, CA · California$63.89+$11.35
- Washington, DC area · District of Columbia$64.67+$12.13
- Miami, FL · Florida$60.90+$8.36
- Chicago, IL · Illinois$59.25+$6.71
- Manhattan, NY · New York$65.02+$12.48
- Alaska · Alaska$67.02+$14.48
Other areas in Iowa first, then benchmark localities. Bars start at $0.
Every other payment area
| Payment locality | Office | Facility |
|---|---|---|
| AlabamaAlabama | $51.30 | $22.66 |
| ArkansasArkansas | $50.60 | $22.49 |
| ArizonaArizona | $55.36 | $23.64 |
| Bakersfield, CACalifornia | $60.11 | $24.23 |
| Chico, CACalifornia | $59.95 | $24.08 |
| El Centro, CACalifornia | $59.96 | $24.08 |
| Fresno, CACalifornia | $59.95 | $24.08 |
| Hanford, CACalifornia | $59.95 | $24.08 |
| Madera, CACalifornia | $59.95 | $24.08 |
| Merced, CACalifornia | $59.95 | $24.08 |
| Modesto, CACalifornia | $59.95 | $24.08 |
| Napa, CACalifornia | $69.14 | $26.00 |
| Oxnard, CACalifornia | $63.56 | $24.87 |
| Redding, CACalifornia | $59.95 | $24.08 |
| Rest of CaliforniaCalifornia | $59.95 | $24.08 |
| Riverside, CACalifornia | $60.50 | $24.62 |
| Sacramento, CACalifornia | $62.83 | $24.76 |
| Salinas, CACalifornia | $62.59 | $24.65 |
| San Diego, CACalifornia | $63.99 | $24.84 |
| Marin County, CACalifornia | $73.11 | $26.95 |
| San Francisco, CACalifornia | $73.05 | $26.90 |
| San Benito County, CACalifornia | $74.71 | $27.51 |
| Santa Clara County, CACalifornia | $74.48 | $27.28 |
| San Luis Obispo, CACalifornia | $61.59 | $24.31 |
| Santa Cruz, CACalifornia | $64.55 | $24.78 |
| Santa Maria, CACalifornia | $62.80 | $24.64 |
| Santa Rosa, CACalifornia | $65.20 | $25.00 |
| Stockton, CACalifornia | $59.95 | $24.08 |
| Vallejo, CACalifornia | $69.06 | $25.92 |
| Visalia, CACalifornia | $59.95 | $24.08 |
| Yuba City, CACalifornia | $59.95 | $24.08 |
| ColoradoColorado | $59.06 | $24.23 |
| ConnecticutConnecticut | $60.40 | $25.15 |
| DelawareDelaware | $56.24 | $23.90 |
| Fort Lauderdale, FLFlorida | $58.63 | $25.47 |
| Rest of FloridaFlorida | $55.95 | $24.65 |
| Atlanta, GAGeorgia | $57.78 | $24.52 |
| Rest of GeorgiaGeorgia | $52.99 | $23.79 |
| Hawaii, Guam, HIHawaii | $61.29 | $24.08 |
| IdahoIdaho | $52.86 | $22.74 |
| East St. Louis, ILIllinois | $55.43 | $25.31 |
| Rest of IllinoisIllinois | $54.41 | $24.52 |
| Suburban Chicago, ILIllinois | $59.22 | $25.60 |
| IndianaIndiana | $53.14 | $22.80 |
| KansasKansas | $52.30 | $22.71 |
| KentuckyKentucky | $52.41 | $23.31 |
| New Orleans, LALouisiana | $54.76 | $23.96 |
| Rest of LouisianaLouisiana | $52.33 | $23.36 |
| Metropolitan Boston, MAMassachusetts | $64.68 | $25.60 |
| Rest of MassachusettsMassachusetts | $58.73 | $24.27 |
| Baltimore area, MDMaryland | $60.23 | $25.11 |
| Rest of MarylandMaryland | $57.27 | $24.15 |
| Rest of MaineMaine | $53.10 | $22.99 |
| Southern Maine, MEMaine | $55.82 | $23.38 |
| Detroit, MIMichigan | $56.59 | $25.01 |
| Rest of MichiganMichigan | $53.68 | $23.80 |
| MinnesotaMinnesota | $56.71 | $23.03 |
| Metropolitan Kansas City, MOMissouri | $54.42 | $23.68 |
| Metropolitan St. Louis, MOMissouri | $54.96 | $23.80 |
| Rest of MissouriMissouri | $51.48 | $23.27 |
| MississippiMississippi | $51.05 | $22.87 |
| MontanaMontana | $56.78 | $24.05 |
| North CarolinaNorth Carolina | $53.63 | $23.09 |
| North DakotaNorth Dakota | $55.79 | $23.06 |
| NebraskaNebraska | $52.81 | $22.60 |
| New HampshireNew Hampshire | $58.13 | $24.06 |
| Northern New JerseyNew Jersey | $64.06 | $26.09 |
| Rest of New JerseyNew Jersey | $61.13 | $25.38 |
| New MexicoNew Mexico | $53.96 | $23.94 |
| NevadaNevada | $56.54 | $23.78 |
| NYC suburbs and Long Island, NYNew York | $66.50 | $27.58 |
| Poughkeepsie and northern NYC suburbs, NYNew York | $61.52 | $25.67 |
| Queens, NYNew York | $65.54 | $26.85 |
| Rest of New YorkNew York | $54.38 | $23.29 |
| OhioOhio | $53.48 | $23.60 |
| OklahomaOklahoma | $52.33 | $23.10 |
| Portland, OROregon | $60.85 | $24.49 |
| Rest of OregonOregon | $56.13 | $23.53 |
| Metropolitan Philadelphia, PAPennsylvania | $58.97 | $24.90 |
| Rest of PennsylvaniaPennsylvania | $53.57 | $23.52 |
| Puerto RicoPuerto Rico | $57.18 | $24.08 |
| Rhode IslandRhode Island | $58.18 | $24.37 |
| South CarolinaSouth Carolina | $53.64 | $23.39 |
| South DakotaSouth Dakota | $55.67 | $22.94 |
| TennesseeTennessee | $52.54 | $22.79 |
| Austin, TXTexas | $58.83 | $24.20 |
| Beaumont, TXTexas | $53.24 | $23.45 |
| Brazoria, TXTexas | $56.21 | $23.77 |
| Dallas, TXTexas | $56.55 | $23.94 |
| Fort Worth, TXTexas | $56.19 | $23.91 |
| Galveston, TXTexas | $56.36 | $23.86 |
| Houston, TXTexas | $57.28 | $24.78 |
| Rest of TexasTexas | $54.68 | $23.61 |
| UtahUtah | $54.33 | $23.56 |
| VirginiaVirginia | $55.64 | $23.47 |
| Virgin Islands, VIUnited States Virgin Islands | $57.18 | $24.08 |
| VermontVermont | $55.58 | $23.17 |
| Rest of WashingtonWashington | $58.62 | $24.15 |
| King County, WAWashington | $65.97 | $25.81 |
| WisconsinWisconsin | $54.03 | $22.67 |
| West VirginiaWest Virginia | $52.51 | $24.07 |
| WyomingWyoming | $56.35 | $23.61 |
11900 rates by state
Office rate range in each state. Select a state to see its payment localities.
Explore a state
Local rates. Clear comparisons.
Hover or focus a tile to see its rate range. Select it to open the state’s fee schedule.
$50.60
$67.33
Color shows the midpoint of each state’s locality range.
View every state and territory as a table
| State / territory | Office rate range | Localities |
|---|---|---|
| AK | $67.02 | 1 |
| AL | $51.30 | 1 |
| AR | $50.60 | 1 |
| AZ | $55.36 | 1 |
| CA | $59.95–$74.71 | 29 |
| CO | $59.06 | 1 |
| CT | $60.40 | 1 |
| DC | $64.67 | 1 |
| DE | $56.24 | 1 |
| FL | $55.95–$60.90 | 3 |
| GA | $52.99–$57.78 | 2 |
| GU | $61.29 | 1 |
| HI | $61.29 | 1 |
| IA | $52.54 | 1 |
| ID | $52.86 | 1 |
| IL | $54.41–$59.25 | 4 |
| IN | $53.14 | 1 |
| KS | $52.30 | 1 |
| KY | $52.41 | 1 |
| LA | $52.33–$54.76 | 2 |
| MA | $58.73–$64.68 | 2 |
| MD | $57.27–$64.67 | 3 |
| ME | $53.10–$55.82 | 2 |
| MI | $53.68–$56.59 | 2 |
| MN | $56.71 | 1 |
| MO | $51.48–$54.96 | 3 |
| MS | $51.05 | 1 |
| MT | $56.78 | 1 |
| NC | $53.63 | 1 |
| ND | $55.79 | 1 |
| NE | $52.81 | 1 |
| NH | $58.13 | 1 |
| NJ | $61.13–$64.06 | 2 |
| NM | $53.96 | 1 |
| NV | $56.54 | 1 |
| NY | $54.38–$66.50 | 5 |
| OH | $53.48 | 1 |
| OK | $52.33 | 1 |
| OR | $56.13–$60.85 | 2 |
| PA | $53.57–$58.97 | 2 |
| PR | $57.18 | 1 |
| RI | $58.18 | 1 |
| SC | $53.64 | 1 |
| SD | $55.67 | 1 |
| TN | $52.54 | 1 |
| TX | $53.24–$58.83 | 8 |
| UT | $54.33 | 1 |
| VA | $55.64–$64.67 | 2 |
| VI | $57.18 | 1 |
| VT | $55.58 | 1 |
| WA | $58.62–$65.97 | 2 |
| WI | $54.03 | 1 |
| WV | $52.51 | 1 |
| WY | $56.35 | 1 |
How the 11900 rate is calculated
Each of 11900’s three RVUs is multiplied by a geographic index (GPCI) for the payment locality, added up, and multiplied by the conversion factor. Drag the indexes or enter a ZIP to see what moves the rate.
How the rate is built · 11900
RVUs × geographic indexes × conversion factor
Work0.51
0.51 RVUs× 1.000 GPCI
Practice expense1.14
1.14 RVUs× 1.000 GPCI
Malpractice0.05
0.05 RVUs× 1.000 GPCI
Adjusted RVUs
1.7000
Conversion factor
$33.4009
Medicare rate
$56.78
Every GPCI starts at 1.000, the national rate. Enter a ZIP or drag a slider.
The exact Iowa inputs and CMS source lines
PPRRVU2026_Oct_nonQPP.csv
1,379
- Code
- 11900
- Physician work
- 0.51
- Practice expense
- 1.14
- Malpractice
- 0.05
GPCI2026.csv
53
- Locality
- Iowa
- Physician work
- 1.000
- Practice expense
- 0.915
- Malpractice
- 0.397
| Component | RVU | Locality factor | Adjusted |
|---|---|---|---|
| Physician work | 0.51 | × 1.000 | 0.5100 |
| Practice expense | 1.14 | × 0.915 | 1.0431 |
| Malpractice | 0.05 | × 0.397 | 0.0199 |
| Total RVUs | 1.5729 | ||
| Conversion factor | × 33.4009 | ||
Office rate, Iowa$52.54
Office: (0.51 × 1 + 1.14 × 0.915 + 0.05 × 0.397) × $33.4009 = $52.54
Facility: (0.51 × 1 + 0.16 × 0.915 + 0.05 × 0.397) × $33.4009 = $22.59
Payment rules and modifiers for 11900
The CMS indicators that decide how 11900 is paid alongside other services.
CMS payment indicators · 11900
Lesion injection, up to seven lesions
| Rule | CMS value | What it means |
|---|---|---|
| Global period | 000 | Same-day global: pre- and post-op care on the day of the procedure is included. |
| Multiple procedures | 2 | Standard reduction: highest-valued procedure at 100%, others at 50%. |
| Bilateral (modifier 50) | 0 | The 150% bilateral adjustment doesn’t apply. |
| Assistant at surgery (80/81/82/AS) | 1 | Not paid (statutory restriction). |
| Co-surgeons (62) | 0 | Not permitted. |
| Team surgery (66) | 0 | Not permitted. |
| Professional/technical | 0 | Physician service: no professional/technical split. |
What modifiers do to the payment
Modifier 51 · payment effect
With and without the modifier
11900 without 51 · national office
$56.78
Lesion injection, up to seven lesions
11900-51 · Second procedure: 50%
$28.39
When this isn’t the highest-valued procedure in the session, Medicare pays 50% of its fee schedule amount (the highest is paid at 100%).
How 11900 has changed in Iowa
11900 · Office / nonfacility
$52.54
Effective 2026-10-01
The base rate is $1.02 higher than on 2025-10-01, moving from $51.52 to $52.54 (2.0%).
It is unchanged from the immediately preceding available release, effective 2026-07-01.
One bar per available release, ordered by effective date. Missing rates remain gaps. These comparisons hold the code, setting and locality identifiers constant; they do not isolate which policy or input caused a change.
What changed, release by release
January 1, 2026
RVU26A
$51.52changed to$52.54
- Conversion factor 32.3465 changed to 33.4009
- Work RVU 0.52 changed to 0.51
- Practice expense RVU 1.15 changed to 1.14
- Practice expense GPCI 0.913 changed to 0.915
- Malpractice GPCI 0.457 changed to 0.397
Held through RVU26B, RVU26C, RVU26D.
January 1, 2025
RVU25A
$53.17changed to$51.52
- Conversion factor 33.2875 changed to 32.3465
- Malpractice RVU 0.06 changed to 0.05
Held through RVU25B, RVU25C, RVU25D.
March 9, 2024
RVU24AR
$52.30changed to$53.17
- Conversion factor 32.7442 changed to 33.2875
Held through RVU24B, RVU24C, RVU24D.
January 1, 2024
RVU24A
$53.36changed to$52.30
- Conversion factor 33.8872 changed to 32.7442
- Practice expense RVU 1.13 changed to 1.15
- Practice expense GPCI 0.910 changed to 0.913
- Malpractice GPCI 0.441 changed to 0.457
January 1, 2023
RVU23A
$53.57changed to$53.36
- Conversion factor 34.6062 changed to 33.8872
- Practice expense RVU 1.11 changed to 1.13
- Malpractice RVU 0.05 changed to 0.06
- Practice expense GPCI 0.907 changed to 0.910
- Malpractice GPCI 0.425 changed to 0.441
Held through RVU23B, RVU23C, RVU23D.
January 1, 2022
RVU22A
$53.07changed to$53.57
- Conversion factor 34.8931 changed to 34.6062
- Practice expense RVU 1.08 changed to 1.11
Held through RVU22B, RVU22C, RVU22D.
January 1, 2021
RVU21A
$51.94changed to$53.07
- Conversion factor 36.0896 changed to 34.8931
- Practice expense RVU 0.99 changed to 1.08
- Malpractice GPCI 0.424 changed to 0.425
Held through RVU21B, RVU21C, RVU21D.
January 1, 2020
RVU20A
$50.86changed to$51.94
- Conversion factor 36.0391 changed to 36.0896
- Practice expense RVU 0.95 changed to 0.99
- Malpractice RVU 0.07 changed to 0.05
- Malpractice GPCI 0.423 changed to 0.424
Held through RVU20B, RVU20C, RVU20D.
January 1, 2019
RVU19A
$52.76changed to$50.86
- Conversion factor 35.9996 changed to 36.0391
- Practice expense RVU 1.01 changed to 0.95
Held through RVU19B, RVU19C, RVU19D.
January 1, 2018
RVU18AR1
$51.86changed to$52.76
- Conversion factor 35.8887 changed to 35.9996
- Practice expense RVU 0.99 changed to 1.01
- Practice expense GPCI 0.902 changed to 0.907
- Malpractice GPCI 0.458 changed to 0.423
Held through RVU18B, RVU18C, RVU18D.
January 1, 2017
RVU17A
$51.29changed to$51.86
- Conversion factor 35.8043 changed to 35.8887
- Practice expense RVU 0.98 changed to 0.99
- Practice expense GPCI 0.896 changed to 0.902
- Malpractice GPCI 0.493 changed to 0.458
Held through RVU17B, RVU17C, RVU17D.
January 1, 2016
RVU16A
$51.30changed to$51.29
- Conversion factor 35.9335 changed to 35.8043
- Malpractice RVU 0.06 changed to 0.07
Held through RVU16B, RVU16C, RVU16D.
July 1, 2015
RVU15C
$51.05changed to$51.30
- Conversion factor 35.7547 changed to 35.9335
Held through RVU15D.
January 1, 2015
RVU15A
$50.18changed to$51.05
- Conversion factor 35.8228 changed to 35.7547
- Practice expense RVU 0.95 changed to 0.98
- Malpractice RVU 0.07 changed to 0.06
- Practice expense GPCI 0.892 changed to 0.896
- Malpractice GPCI 0.475 changed to 0.493
Held through RVU15B.
January 1, 2014
RVU14A
$51.37changed to$50.18
- Conversion factor 34.0230 changed to 35.8228
- Practice expense RVU 1.08 changed to 0.95
- Practice expense GPCI 0.887 changed to 0.892
- Malpractice GPCI 0.456 changed to 0.475
Held through RVU14B, RVU14C, RVU14D.
January 1, 2013
RVU13AR
Earliest loaded release: $51.37
Held through RVU13B, RVU13C, RVU13D.
| Effective from | Office | Facility | CMS release |
|---|---|---|---|
| 2026-10-01 | $52.54 | $22.59 | RVU26D |
| 2026-07-01 | $52.54 | $22.59 | RVU26C |
| 2026-04-01 | $52.54 | $22.59 | RVU26B |
| 2026-01-01 | $52.54 | $22.59 | RVU26A |
| 2025-10-01 | $51.52 | $26.71 | RVU25D |
| 2025-07-01 | $51.52 | $26.71 | RVU25C |
| 2025-04-01 | $51.52 | $26.71 | RVU25B |
| 2025-01-01 | $51.52 | $26.71 | RVU25A |
| 2024-10-01 | $53.17 | $27.64 | RVU24D |
| 2024-07-01 | $53.17 | $27.64 | RVU24C |
| 2024-04-01 | $53.17 | $27.64 | RVU24B |
| 2024-03-09 | $53.17 | $27.64 | RVU24AR |
| 2024-01-01 | $52.30 | $27.19 | RVU24A |
| 2023-10-01 | $53.36 | $28.08 | RVU23D |
| 2023-07-01 | $53.36 | $28.08 | RVU23C |
| 2023-04-01 | $53.36 | $28.08 | RVU23B |
| 2023-01-01 | $53.36 | $28.08 | RVU23A |
| 2022-10-01 | $53.57 | $27.83 | RVU22D |
| 2022-07-01 | $53.57 | $27.83 | RVU22C |
| 2022-04-01 | $53.57 | $27.83 | RVU22B |
| 2022-01-01 | $53.57 | $27.83 | RVU22A |
| 2021-10-01 | $53.07 | $28.38 | RVU21D |
| 2021-07-01 | $53.07 | $28.38 | RVU21C |
| 2021-04-01 | $53.07 | $28.38 | RVU21B |
| 2021-01-01 | $53.07 | $28.38 | RVU21A |
| 2020-10-01 | $51.94 | $29.35 | RVU20D |
| 2020-07-01 | $51.94 | $29.35 | RVU20C |
| 2020-04-01 | $51.94 | $29.35 | RVU20B |
| 2020-01-01 | $51.94 | $29.35 | RVU20A |
| 2019-10-01 | $50.86 | $29.94 | RVU19D |
| 2019-07-01 | $50.86 | $29.94 | RVU19C |
| 2019-04-01 | $50.86 | $29.94 | RVU19B |
| 2019-01-01 | $50.86 | $29.94 | RVU19A |
| 2018-10-01 | $52.76 | $29.91 | RVU18D |
| 2018-07-01 | $52.76 | $29.91 | RVU18C |
| 2018-04-01 | $52.76 | $29.91 | RVU18B |
| 2018-01-01 | $52.76 | $29.91 | RVU18AR1 |
| 2017-10-01 | $51.86 | $29.85 | RVU17D |
| 2017-07-01 | $51.86 | $29.85 | RVU17C |
| 2017-04-01 | $51.86 | $29.85 | RVU17B |
| 2017-01-01 | $51.86 | $29.85 | RVU17A |
| 2016-10-01 | $51.29 | $29.80 | RVU16D |
| 2016-07-01 | $51.29 | $29.80 | RVU16C |
| 2016-04-01 | $51.29 | $29.80 | RVU16B |
| 2016-01-01 | $51.29 | $29.80 | RVU16A |
| 2015-10-01 | $51.30 | $29.73 | RVU15D |
| 2015-07-01 | $51.30 | $29.73 | RVU15C |
| 2015-04-01 | $51.05 | $29.58 | RVU15B |
| 2015-01-01 | $51.05 | $29.58 | RVU15A |
| 2014-10-01 | $50.18 | $29.41 | RVU14D |
| 2014-07-01 | $50.18 | $29.41 | RVU14C |
| 2014-04-01 | $50.18 | $29.41 | RVU14B |
| 2014-01-01 | $50.18 | $29.41 | RVU14A |
| 2013-10-01 | $51.37 | $29.04 | RVU13D |
| 2013-07-01 | $51.37 | $29.04 | RVU13C |
| 2013-04-01 | $51.37 | $29.04 | RVU13B |
| 2013-01-01 | $51.37 | $29.04 | RVU13AR |
Where the Iowa rate applies
Iowa is a Medicare payment area, not a city. Our Census mapping connects it to 1026 cities and communities in Iowa. Some span more than one payment area; confirm with the service ZIP.
- Ackley
- Ackworth
- Adair
- Adel
- Afton
- Agency
- Ainsworth
- Akron
11900 billing questions
How many lesions qualify for 11900?
Report 11900 for treatment of one through seven lesions in the session. Use 11901 when more than seven lesions are treated.
Do separate injections into one lesion count as multiple lesions?
No. Select the code by the number of distinct lesions treated, not the number of needle passes or injection sites within a lesion.
Can the injected medication be billed separately?
The medication may be reported separately when applicable. Document the drug and dose, and follow the applicable drug-code requirements.
Is modifier 50 appropriate when lesions are on both sides of the body?
No. CMS identifies bilateral adjustment as inappropriate for 11900; report the service based on the number of lesions treated.
How does the 0-day global period affect same-day care?
Same-day preoperative and postoperative care is included in the procedure. CMS applies the standard multiple-procedure reduction when other procedures are performed in the same session.
Can an assistant or co-surgeon be reported?
CMS does not pay an assistant at surgery for this code. Co-surgeons and team surgery are not permitted.
Where these rates come from
FeeBase calculates base physician payments from CMS work, practice-expense and malpractice RVUs, adjusted by each locality’s geographic indexes and the conversion factor. Services without a published rate are labeled, never given a made-up amount. Amounts are Medicare allowed amounts before claim adjustments: not a patient’s bill or a commercial rate.
CMS RVU26D · effective Oct 1, 2026 through the day before Jan 1, 2027
Show the CMS file lines behind this rate
Fee sheets · Coming soon
Put 11900 and the rest of your codes on one sheet
Your codes at your locality, with payer contracts beside Medicare.
Join the waitlist