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DR. NICHOLAS GASTON CALLIHAN M.D.
NPI 1821482357
Emergency Medicine in Houston, TX

Active since March 23, 2015PECOS EnrolledAccepts Medicare Assignment
82.38/100
CMS Quality Rating
1635 NORTH LOOP W, HOUSTON, TX 77008(713) 867-2000 Get Directions Write a Review

NPPES record last updated: September 13, 2024. Verified against the NPPES registry weekly; last sync: October 25, 2026.

Record update history: Sep 13, 2024, Jun 21, 2021, Aug 27, 2018 (3 updates tracked since 2018).

About Dr. Nicholas Gaston Callihan M.d. NPPES

Official registry information on file with the National Plan and Provider Enumeration System.

DR. NICHOLAS GASTON CALLIHAN M.D. (NPI 1821482357) is an individual emergency medicine provider in Houston, Texas, licensed in Texas (R6532) and active in the NPI registry since March 2015. He is enrolled in Medicare PECOS, is affiliated with Memorial Hermann - Texas Medical Center, and maintains a secondary practice location in Houston.

NPPES Registry Identity

NPI1821482357
Entity TypeIndividualMale
Primary Taxonomy207P00000X
Provider Legal NameDR. NICHOLAS GASTON CALLIHANCredential: M.D.
Location Address1635 NORTH LOOP WHouston, TX 77008
Mailing Address909 Frostwood DrHouston, TX 77024-2301 · (832) 655-5665
Phone(713) 867-2000
Sole ProprietorNo
Medical School CMSMedical College Of Georgia School Of MedicineGraduated 2015
Enumeration DateMarch 23, 2015
Last NPPES UpdateSeptember 13, 20243 updates tracked since enumeration
NPPES CertifiedSeptember 13, 2024
✔ NPI 1821482357 is a valid, active identifier and passes the ISO check-digit test.

Specialties & Licenses

★ Primary SpecialtyEmergency MedicineAllopathic & Osteopathic Physicians
Taxonomy Code207P00000X
License✔ Licensed in TX · R6532
Definition
An emergency physician focuses on the immediate decision making and action necessary to prevent death or any further disability both in the pre-hospital setting by directing emergency medical technicians and in the emergency department. The emergency physician provides immediate recognition, evaluation, care, stabilization and disposition of a generally diversified population of adult and pediatric patients in response to acute illness and injury.
1635 NORTH LOOP W, Houston, TX 77008
Open in Google Maps ↗

Secondary Practice Location 1

Location 16431 Fannin St, Suite JJL 431Houston, TX 77030-1501 · Phone (713) 500-7882 · Fax (713) 500-0758

Accepted Insurance

The full list of accepted plans is on the Insurance tab. Issuers include Blue Cross and Blue Shield of Texas, Oscar Insurance Company, UnitedHealthcare.Insurance ›

Medicare Participation & PECOS CMS

Medicare enrollment, assignment, billing reassignment, and ordering and referring status from CMS.

Medicare Enrollment Status

✔

Enrolled in Medicare and accepts Medicare assignment

Dr. Nicholas Gaston Callihan M.d. is registered in PECOS and agrees to accept the Medicare-approved amount as full payment. Medicare patients are not billed beyond the standard deductible and coinsurance.

PECOS PAC ID3971866443
PECOS Enrollment IDI20180416000371
Eligible to Order & Refer✔ Part B Labs & Imaging✔ Durable Medical Equipment✔ Home Health Agency✔ Power Mobility DevicesPer the CMS Ordering and Referring file. Eligibility means Medicare pays claims that this provider orders or refers for these categories.

Medicare Billing Reassignments

5

Medicare enrollment records show Nicholas Callihan reassigns Medicare billing to 5 organizations. Each organization bills Medicare for the services this provider delivers there; the nearest is listed first.

Ut Physicians
7.0 mi
Anesthesiology
6410 FANNIN ST, 1500
Houston, TX 77030
  • Reassigned Medicare billing, Texas enrollment
  • 3,111 clinicians in this Medicare group
NPI 1033157821 (832) 325-7325
Memorial Hermann Hospital Based Physician Group
7.2 mi
Emergency Medicine
929 GESSNER RD STE 2700
Houston, TX 77024
  • Reassigned Medicare billing, Texas enrollment
  • 408 clinicians in this Medicare group
NPI 1295363497 (713) 242-2712
Acs Primary Care Physicians Southwest, PA
284 mi
Emergency Medicine
1900 HOSPITAL BLVD
Gainesville, TX 76240
  • Reassigned Medicare billing, Texas enrollment
  • 1,193 clinicians in this Medicare group
NPI 1538101019 (925) 924-1600
Concord Medical Group PLLC
459 mi
Emergency Medicine
1602 AVENUE Q
Lubbock, TX 79401
  • Reassigned Medicare billing, Texas enrollment
  • 1,338 clinicians in this Medicare group
NPI 1083630610 (888) 264-0330
Concord Medical Group Of Texas PLLC
459 mi
Emergency Medicine
1602 AVENUE Q
Lubbock, TX 79401
  • Reassigned Medicare billing, Texas enrollment
  • 1,439 clinicians in this Medicare group
NPI 1750790762 (888) 264-0330

Source: CMS Revalidation Reassignment List, October 2026 release. Reassignment records can lag staffing changes; confirm a current affiliation with the organization.

Areas of Expertise CMS Part B claims 4

Services this provider delivered to Medicare fee-for-service patients, from the CMS Medicare utilization data. Higher counts generally reflect more experience with a service; care delivered outside Medicare is not included.

Emergency department visit with high level of medical decision making 99285
An emergency department visit for severe conditions is when you urgently seek medical help due to serious health issues. These could be severe injuries, breathing problems, unbearable pain, or sudden severe illness. Doctors and nurses will provide immediate care to stabilize your condition.
162 services161 patients
Emergency department visit with moderate level of medical decision making 99284
An emergency department visit for a high-severity issue means you're experiencing a serious health problem that needs immediate attention. This could be a severe injury, serious illness, or life-threatening condition. Medical professionals will provide urgent care to stabilize your condition.
49 services49 patients
Critical care, first 30-74 minutes 99291
Critical care involves immediate and constant attention by a team of specially-trained health professionals. It's for patients with life-threatening conditions, requiring first 30-74 minutes of intense monitoring and treatment.
26 services26 patients
Routine electrocardiogram (ecg) using at least 12 leads with interpretation and report only 93010
A routine electrocardiogram (ECG) with 12 leads is a simple, non-invasive test that records the electrical activity of your heart. It helps in identifying heart conditions by detecting irregularities in your heart rhythms. The results are interpreted and a report is provided.
22 services22 patients

Hospital Affiliations CMS Care Compare 2

Hospitals where this provider delivers care, identified from recent Medicare claims and place-of-service records.

Memorial Hermann - Texas Medical Center

Acute Care Hospitals · Houston, TX
3/5 CMS rating
OwnershipVoluntary non-profit - Private
CMS Certification Number450068
Location6411 FanninHouston, TX 77030 · Harris County
Emergency services Birthing friendly

Memorial Hermann Hospital System

Acute Care Hospitals · Houston, TX
3/5 CMS rating
OwnershipVoluntary non-profit - Private
CMS Certification Number450184
Location1635 North Loop WestHouston, TX 77008 · Harris County
Emergency services Birthing friendly

Physician Visit Costs CMS claims · ZIP area

Typical Medicare office-visit costs in the 77008 ZIP code area, from fee-for-service claims. These are area statistics, not this provider’s prices; actual charges vary by service and coverage.

New Patient
$90.40 typical visit price
range $58.24 – $176.98
Typical copayment $22.60 (range $14.56 – $44.24)
Most-billed visit code 99203
Established Patient
$102.71 typical visit price
range $18.60 – $143.93
Typical copayment $25.67 (range $4.65 – $35.98)
Most-billed visit code 99214
Amounts reflect what Medicare beneficiaries in this ZIP area are typically charged for office visits. Patients with other coverage should check their individual plans.

Medicare Quality Performance CMS QPP · MIPS

Performance in the CMS Quality Payment Program: the MIPS final score across four weighted categories, and the individual quality measures reported to Medicare.

82.38/100
MIPS Final ScoreMerit-based Incentive Payment System · CMS Quality Payment Program
Scored as part of a group practice
Quality79.23
Promoting Interoperability100
Improvement Activities40
Cost58.5

Other Providers at the Same Location NPPES 20

Providers registered at the same practice address, or within the immediate area, according to the NPPES registry.

HYUNG J KIM MD
Anesthesiology
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 540-6980
THANG HLEI KIM
Nurse Practitioner (Acute Care)
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 867-2000
DAYNA EVELYN MCDANIEL CRNA
Nurse Anesthetist, Certified Registered
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 867-2000
STACEY WUNGSEE LAU OTR
Occupational Therapist
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 803-6778
LOUIS T PENA CRNA
Nurse Anesthetist, Certified Registered
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 400-2990
MEMORIAL HERMANN HEALTH SYSTEM
Clinic/Center (Radiology)
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 867-3336
TATSUO YAMAKAWA M.D.
Emergency Medicine
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (713) 338-6565
MAHREEN UMATIYA FNP-C
Nurse Practitioner
1635 NORTH LOOP W
HOUSTON, TX 77008
Harris County (904) 372-3943

Frequently Asked Questions NPPES & CMS

Common questions about this NPI record, answered from the official NPPES registry and CMS datasets shown on this page.

What is Nicholas Callihan's NPI number?

The NPI number for Nicholas Callihan is 1821482357. It was assigned to this individual provider in the NPPES registry on March 23, 2015.

Where is Nicholas Callihan located?

Nicholas Callihan practices at 1635 North Loop W, Houston, TX 77008. The listed phone number is (713) 867-2000.

What is Nicholas Callihan's specialty?

The primary specialty registered for this NPI is Emergency Medicine with taxonomy code 207P00000X.

Is Nicholas Callihan enrolled in Medicare?

Yes. Nicholas Callihan is registered in the Medicare PECOS system and accepts Medicare assignment, which means accepting the Medicare-approved amount as payment in full for covered services.

Which organizations bill Medicare for Nicholas Callihan's services?

According to the CMS Revalidation Reassignment List (October 2026 release), Nicholas Callihan reassigns Medicare benefits to 5 organizations: Ut Physicians (Houston, TX), Memorial Hermann Hospital Based Physician Group (Houston, TX), Acs Primary Care Physicians Southwest, PA (Gainesville, TX), Concord Medical Group PLLC (Lubbock, TX) and Concord Medical Group Of Texas PLLC (Lubbock, TX). Each reassignment is filed with Medicare on form CMS-855R, signed by both the clinician and the organization, and lets the organization bill Medicare and receive payment for Nicholas Callihan's services. Reassignment records can lag staffing changes; confirm current arrangements with the organization.

What insurance does Nicholas Callihan accept?

Health plans from Blue Cross and Blue Shield of Texas, Oscar Insurance Company and UnitedHealthcare list Nicholas Callihan as in-network in at least one marketplace plan. Coverage varies by plan and year; verify with the insurer or the provider before a visit.

Is Nicholas Callihan affiliated with any hospitals?

According to CMS data, Nicholas Callihan is affiliated with Memorial Hermann - Texas Medical Center and Memorial Hermann Hospital System.

When was this NPI record last updated?

The NPPES record for Nicholas Callihan was last updated on September 13, 2024. NPI Profile syncs weekly with the NPPES registry data releases published by CMS. This NPI record was last updated 2 years ago. If this record has changed at CMS more recently, you can request an on-demand re-check against the live CMS registry, directly from this page.