Clinical Focus

  • Clinical Informatics
  • Clinical Pathology

Honors & Awards

  • Chair, Chief Resident Council, Stanford University (2016-2017)
  • Chief Resident, Informatics, Stanford University - Pathology Department (2015-2017)
  • Medical Scientist Training Program, NIH (2007-2014)

Professional Education

  • Medical Education: Albert Einstein College of Medicine (2014) NY
  • Board Certification: American Board of Pathology, Clinical Pathology (2017)
  • Residency: Stanford University Pathology Residency CA
  • PhD, Albert Einstein College of Medicine, Systems & Computational Biology (2014)
  • B.S, University of North Carolina at Chapel Hill, Computer Science and Biology (2005)

All Publications

  • It is time to learn from patients like mine. NPJ digital medicine Gombar, S., Callahan, A., Califf, R., Harrington, R., Shah, N. H. 2019; 2: 16


    Clinicians are often faced with situations where published treatment guidelines do not provide a clear recommendation. In such situations, evidence generated from similar patients' data captured in electronic health records (EHRs) can aid decision making. However, challenges in generating and making such evidence available have prevented its on-demand use to inform patient care. We propose that a specialty consultation service staffed by a team of medical and informatics experts can rapidly summarize 'what happened to patients like mine' using data from the EHR and other health data sources. By emulating a familiar physician workflow, and keeping experts in the loop, such a service can translate physician inquiries about situations with evidence gaps into actionable reports. The demand for and benefits gained from such a consult service will naturally vary by practice type and data robustness. However, we cannot afford to miss the opportunity to use the patient data captured every day via EHR systems to close the evidence gap between available clinical guidelines and realities of clinical practice. We have begun offering such a service to physicians at our academic medical center and believe that such a service should be core offering by clinical informatics professional throughout the country. Only if we launch such efforts broadly can we systematically study the utility of learning from the record of routine clinical practice.

    View details for DOI 10.1038/s41746-019-0091-3

    View details for PubMedID 31304364

    View details for PubMedCentralID PMC6550176

  • It is time to learn from patients like mine NPJ DIGITAL MEDICINE Gombar, S., Callahan, A., Califf, R., Harrington, R., Shah, N. H. 2019; 2
  • Implementation of Whole-Blood Impedance Aggregometry for Heparin-Induced Thrombocytopenia Functional Assay and Case Discussion. American journal of clinical pathology Jin, J. n., Baker, S. A., Hall, E. T., Gombar, S. n., Bao, A. n., Zehnder, J. L. 2019; 152 (1): 50–58


    The diagnosis of heparin-induced thrombocytopenia (HIT) ideally requires a functional assay to confirm. 14C-serotonin release assay (SRA) as "gold standard" is technically challenging and unsuitable for routine use. We conducted a study to assess the performance of whole-blood impedance aggregometry (WBIA) as a simple and rapid HIT functional assay.Platelet factor 4 (PF4)/immunoglobulin G (IgG) antibody, WBIA, and SRA were tested on 70 patients suspected of having HIT. Patients with a 4Ts score of 4 or more, positive PF4/IgG, and positive SRA were considered HIT positive; others were designated HIT negative.WBIA had 85.7% (6/7) sensitivity and 98.4% (61/62) specificity, which were not statistically different compared with SRA. Sixty-two of 70 patients had concordant results (five positive and 57 negative) by both WBIA and SRA. Eight discordant cases revealed the importance of recognizing donor effect, interferences, and the presence of heparin-independent or non-heparin-dependent antibodies in functional assays.Implementation of WBIA could facilitate timely diagnosis and management of HIT.

    View details for DOI 10.1093/ajcp/aqz013

    View details for PubMedID 31165165

  • Advancing the Use of the ISBT-128 Coding System in Electronic Health Records to Monitor Blood Transfusion Prevalence in the United States Obidi, J., Chada, K., Gruber, J., Dores, G., Storch, E., Williams, A., Banda, J., Gombar, S., Balraj, D., Hayden, R., Hood, D., Falconer, T., Natarajan, K., Allakhverdiiev, E., Dempster, S., Reich, C., Williams, N., Shoaibi, A. WILEY. 2018: 167A
  • Transfusion Trends of Whole Blood and Blood Components in Electronic Health Records and Claims Databases Chada, K., Obidi, J., Gruber, J., Dores, G., Storch, E., Williams, A., Banda, J., Gombar, S., Balraj, D., Hayden, R., Hood, D., Falconer, T., Natarajan, K., Allakhverdiiev, E., Dempster, S., Reich, C., Williams, N., Shoaibi, A. WILEY. 2018: 91A
  • Big data modeling to predict platelet usage and minimize wastage in a tertiary care system PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Guan, L., Tian, X., Gombar, S., Zemek, A. J., Krishnan, G., Scott, R., Narasimhan, B., Tibshirani, R. J., Pham, T. D. 2017; 114 (43): 11368–73


    Maintaining a robust blood product supply is an essential requirement to guarantee optimal patient care in modern health care systems. However, daily blood product use is difficult to anticipate. Platelet products are the most variable in daily usage, have short shelf lives, and are also the most expensive to produce, test, and store. Due to the combination of absolute need, uncertain daily demand, and short shelf life, platelet products are frequently wasted due to expiration. Our aim is to build and validate a statistical model to forecast future platelet demand and thereby reduce wastage. We have investigated platelet usage patterns at our institution, and specifically interrogated the relationship between platelet usage and aggregated hospital-wide patient data over a recent consecutive 29-mo period. Using a convex statistical formulation, we have found that platelet usage is highly dependent on weekday/weekend pattern, number of patients with various abnormal complete blood count measurements, and location-specific hospital census data. We incorporated these relationships in a mathematical model to guide collection and ordering strategy. This model minimizes waste due to expiration while avoiding shortages; the number of remaining platelet units at the end of any day stays above 10 in our model during the same period. Compared with historical expiration rates during the same period, our model reduces the expiration rate from 10.5 to 3.2%. Extrapolating our results to the ∼2 million units of platelets transfused annually within the United States, if implemented successfully, our model can potentially save ∼80 million dollars in health care costs.

    View details for PubMedID 29073058

  • Clostridium difficile PCR Cycle Threshold Predicts Free Toxin JOURNAL OF CLINICAL MICROBIOLOGY Senchyna, F., Gaur, R. L., Gombar, S., Truong, C. Y., Schroeder, L. F., Banaei, N. 2017; 55 (9): 2651–60


    There is no stand-alone Clostridium difficile diagnostic that can sensitively and rapidly detect fecal free toxins. We investigated the performance of the C. difficile PCR cycle threshold (CT ) for predicting free toxin status. Consecutive stool samples (n = 312) positive for toxigenic C. difficile by the GeneXpert C. difficile/Epi tcdB PCR assay were tested with the rapid membrane C. Diff Quik Chek Complete immunoassay (RMEIA). RMEIA toxin-negative samples were tested with the cell cytotoxicity neutralization assay (CCNA) and tgcBIOMICS enzyme-linked immunosorbent assay (ELISA). Using RMEIA alone or in combination with CCNA and/or ELISA as the reference method, the accuracy of CT was measured at different CT cutoffs. Using RMEIA as the reference method, a CT cutoff of 26.35 detected toxin-positive samples with a sensitivity, specificity, positive predictive value, and negative predictive value of 96.0% (95% confidence interval [CI], 90.2% to 98.9%), 65.9% (95% CI, 59.0% to 72.2%), 57.4% (95% CI, 52.7% to 62%), and 97.1% (95% CI, 92.8% to 98.9), respectively. Inclusion of CCNA in the reference method improved CT specificity to 78.0% (95% CI, 70.7% to 84.2%). Intercartridge lot CT variability measured as the average coefficient of variation was 2.8% (95% CI, 1.2% to 3.2%). Standardizing the input stool volume did not improve CT toxin specificity. The median CT values were not significantly different between stool samples with Bristol scores of 5, 6, and 7, between pediatric and adult samples, or between presumptive 027 and non-027 strains. In addition to sensitively detecting toxigenic C. difficile in stool, on-demand PCR may also be used to accurately predict toxin-negative stool samples, thus providing additional results in PCR-positive stool samples to guide therapy.

    View details for PubMedID 28615471

    View details for PubMedCentralID PMC5648702

  • Infection Rates. Journal of clinical microbiology Truong, C. Y., Gombar, S., Wilson, R., Sundararajan, G., Tekic, N., Holubar, M., Shepard, J., Madison, A., Tompkins, L., Shah, N., Deresinski, S., Schroeder, L. F., Banaei, N. 2017


    Health care-onset health care facility-associated Clostridium difficile infection (HO-CDI) is overdiagnosed for several reasons, including the high prevalence of C. difficile colonization and the inability of hospitals to limit testing to patients with clinically significant diarrhea. We conducted a quasiexperimental study from 22 June 2015 to 30 June 2016 on consecutive inpatients with C. difficile test orders at an academic hospital. Real-time electronic patient data tracking was used by the laboratory to enforce testing criteria (defined as the presence of diarrhea [≥3 unformed stools in 24 h] and absence of laxative intake in the prior 48 h). Outcome measures included C. difficile test utilization, HO-CDI incidence, oral vancomycin utilization, and clinical complications. During the intervention, 7.1% (164) and 9.1% (211) of 2,321 C. difficile test orders were canceled due to absence of diarrhea and receipt of laxative therapy, respectively. C. difficile test utilization decreased upon implementation from an average of 208.8 tests to 143.0 tests per 10,000 patient-days (P < 0.001). HO-CDI incidence rate decreased from an average of 13.0 cases to 9.7 cases per 10,000 patient-days (P = 0.008). Oral vancomycin days of therapy decreased from an average of 13.8 days to 9.4 days per 1,000 patient-days (P = 0.009). Clinical complication rates were not significantly different in patients with 375 canceled orders compared with 869 episodes with diarrhea but negative C. difficile results. Real-time electronic clinical data tracking is an effective tool for verification of C. difficile clinical testing criteria and safe reduction of inflated HO-CDI rates.

    View details for DOI 10.1128/JCM.02319-16

    View details for PubMedID 28250001

  • Implementation of Automated Calculation of Free and Bioavailable Testosterone in Epic Beaker Laboratory Information System. Journal of pathology informatics Chung, M. C., Gombar, S. n., Shi, R. Z. 2017; 8: 28


    Automated calculations by laboratory information system (LIS) are efficient and accurate ways of providing calculated laboratory test results. Due to the lack of established advanced mathematical functions and equation logic in LIS software, calculations beyond simple arithmetic functions require a tedious workaround. Free and bioavailable testosterone (BT) calculations require a quadratic solver currently unavailable as ready to use the function on most commercial LIS platforms. We aimed to develop a module within the Epic Beaker LIS to enable automatic quadratic equation solving capability and real-time reporting of calculated free and BT values.We developed and implemented an advanced calculation module from the ground up using existing basic calculation programming functions in the Epic Beaker LIS. A set of calculation variables were created, and mathematical logic and functions were used to link the variables and perform the actual quadratic equation based calculations. Calculations were performed in real-time during result entry events, and calculated results populated the result components in LIS automatically.Free and BT were calculated using instrument measured results of total testosterone, sex hormone binding globulin, and/or serum albumin, by applying equations widely adopted in laboratory medicine for endocrine diseases and disorders. Calculated results in Epic Beaker LIS were then compared and confirmed by manual calculations using Microsoft Excel spreadsheets and scientific calculators to have no discrepancies.Automated calculations of free and BT were successfully implemented and validated, the first of such implementation for the Epic Beaker LIS platform, eliminating the need of offline manual calculations, potential transcription error, and with improved turnaround time. It may serve as a model to build similarly complex equations when the clinical need arises.

    View details for PubMedID 28828199

    View details for PubMedCentralID PMC5545775

  • Plasmacytic posttransplant lymphoproliferative disorder with hyperviscosity syndrome in a child after liver transplant. Hepatology Yang, C. H., Gombar, S., Twist, C. J., Gratzinger, D., Esquivel, C. O., Lau, A. H. 2016

    View details for DOI 10.1002/hep.28657

    View details for PubMedID 27227484

  • MicroRNA transcriptome analysis identifies miR-365 as a novel negative regulator of cell proliferation in Zmpste24-deficient mouse embryonic fibroblasts MUTATION RESEARCH-FUNDAMENTAL AND MOLECULAR MECHANISMS OF MUTAGENESIS Xiong, X., Jung, H. J., Gombar, S., Park, J. Y., Zhang, C., Zheng, H., Ruan, J., Li, J., Kaeberlein, M., Kennedy, B. K., Zhou, Z., Liu, X., Suh, Y. 2015; 777: 69-78


    Zmpste24 is a metalloproteinase responsible for the posttranslational processing and cleavage of prelamin A into mature laminA. Zmpste24(-/-) mice display a range of progeroid phenotypes overlapping with mice expressing progerin, an altered version of lamin A associated with Hutchinson-Gilford progeria syndrome (HGPS). Increasing evidence has demonstrated that miRNAs contribute to the regulation of normal aging process, but their roles in progeroid disorders remain poorly understood. Here we report the miRNA transcriptomes of mouse embryonic fibroblasts (MEFs) established from wild type (WT) and Zmpste24(-/-) progeroid mice using a massively parallel sequencing technology. With data from 19.5 × 10(6) reads from WT MEFs and 16.5 × 10(6) reads from Zmpste24(-/-) MEFs, we discovered a total of 306 known miRNAs expressed in MEFs with a wide dynamic range of read counts ranging from 10 to over 1 million. A total of 8 miRNAs were found to be significantly down-regulated, with only 2 miRNAs upregulated, in Zmpste24(-/-) MEFs as compared to WT MEFs. Functional studies revealed that miR-365, a significantly down-regulated miRNA in Zmpste24(-/-) MEFs, modulates cellular growth phenotypes in MEFs. Overexpression of miR-365 in Zmpste24(-/-) MEFs increased cellular proliferation and decreased the percentage of SA-β-gal-positive cells, while inhibition of miR-365 function led to an increase of SA-β-gal-positive cells in WT MEFs. Furthermore, we identified Rasd1, a member of the Ras superfamily of small GTPases, as a functional target of miR-365. While expression of miR-365 suppressed Rasd1 3' UTR luciferase-reporter activity, this effect was lost with mutations in the putative 3' UTR target-site. Consistently, expression levels of miR-365 were found to inversely correlate with endogenous Rasd1 levels. These findings suggest that miR-365 is down-regulated in Zmpste24(-/-) MEFs and acts as a novel negative regulator of Rasd1. Our comprehensive miRNA data provide a resource to study gene regulatory networks in MEFs.

    View details for DOI 10.1016/j.mrfmmm.2015.04.010

    View details for Web of Science ID 000356736100009

    View details for PubMedID 25983189

    View details for PubMedCentralID PMC4654172

  • SMiRK: an Automated Pipeline for miRNA Analysis. Source journal of genomics Milholland, B., Gombar, S., Suh, Y. 2015; 1 (1)


    Micro RNAs (miRNAs), important regulators of cell function, can be interrogated by high-throughput sequencing in a rapid and cost-effective manner. However, the tremendous amount of data generated by such methods is not easily analyzed. In order to extract meaningful information and draw biological conclusions from miRNA data, many challenges in quality control, alignment, normalization, and analysis must be overcome. Typically, these would only be possible with the dedicated efforts of a specialized computational biologist for a sustained period of time.Here, we present SMiRK, an automated pipeline that allows such tasks to be completed with minimal time and without dedicated bioinformatics personnel. SMiRK's flexibility also allows experienced users to exert more control, if they wish. We describe how SMiRK automatically normalizes the data, removes low-information miRNAs, and produces heatmaps of the processed data. We give details on SMiRK's implementation and use cases for novice and advanced users. As a demonstration of its capabilities, SMiRK was used to rapidly and automatically analyze a dataset taken from the literature.SMiRK is a useful and efficient tool that can be used by investigators at multiple skill levels. Those who lack bioinformatics training can use it to easily and automatically analyze their data, while those with experience will find it beneficial to not need to write tools from scratch.

    View details for PubMedID 26613105

    View details for PubMedCentralID PMC4657868

  • Epigenetics Decouples Mutational from Environmental Robustness. Did It Also Facilitate Multicellularity? PLOS COMPUTATIONAL BIOLOGY Gombar, S., MacCarthy, T., Bergman, A. 2014; 10 (3)


    The evolution of ever increasing complex life forms has required innovations at the molecular level in order to overcome existing barriers. For example, evolving processes for cell differentiation, such as epigenetic mechanisms, facilitated the transition to multicellularity. At the same time, studies using gene regulatory network models, and corroborated in single-celled model organisms, have shown that mutational robustness and environmental robustness are correlated. Such correlation may constitute a barrier to the evolution of multicellularity since cell differentiation requires sensitivity to cues in the internal environment during development. To investigate how this barrier might be overcome, we used a gene regulatory network model which includes epigenetic control based on the mechanism of histone modification via Polycomb Group Proteins, which evolved in tandem with the transition to multicellularity. Incorporating the Polycomb mechanism allowed decoupling of mutational and environmental robustness, thus allowing the system to be simultaneously robust to mutations while increasing sensitivity to the environment. In turn, this decoupling facilitated cell differentiation which we tested by evaluating the capacity of the system for producing novel output states in response to altered initial conditions. In the absence of the Polycomb mechanism, the system was frequently incapable of adding new states, whereas with the Polycomb mechanism successful addition of new states was nearly certain. The Polycomb mechanism, which dynamically reshapes the network structure during development as a function of expression dynamics, decouples mutational and environmental robustness, thus providing a necessary step in the evolution of multicellularity.

    View details for DOI 10.1371/journal.pcbi.1003450

    View details for Web of Science ID 000336509000007

    View details for PubMedID 24604070

    View details for PubMedCentralID PMC3945085

  • Comprehensive microRNA profiling in B-cells of human centenarians by massively parallel sequencing BMC GENOMICS Gombar, S., Jung, H. J., Dong, F., Calder, B., Atzmon, G., Barzilai, N., Tian, X., Pothof, J., Hoeijmakers, J. H., Campisi, J., Vijg, J., Suh, Y. 2012; 13


    MicroRNAs (miRNAs) are small, non-coding RNAs that regulate gene expression and play a critical role in development, homeostasis, and disease. Despite their demonstrated roles in age-associated pathologies, little is known about the role of miRNAs in human aging and longevity.We employed massively parallel sequencing technology to identify miRNAs expressed in B-cells from Ashkenazi Jewish centenarians, i.e., those living to a hundred and a human model of exceptional longevity, and younger controls without a family history of longevity. With data from 26.7 million reads comprising 9.4 × 108 bp from 3 centenarian and 3 control individuals, we discovered a total of 276 known miRNAs and 8 unknown miRNAs ranging several orders of magnitude in expression levels, a typical characteristics of saturated miRNA-sequencing. A total of 22 miRNAs were found to be significantly upregulated, with only 2 miRNAs downregulated, in centenarians as compared to controls. Gene Ontology analysis of the predicted and validated targets of the 24 differentially expressed miRNAs indicated enrichment of functional pathways involved in cell metabolism, cell cycle, cell signaling, and cell differentiation. A cross sectional expression analysis of the differentially expressed miRNAs in B-cells from Ashkenazi Jewish individuals between the 50th and 100th years of age indicated that expression levels of miR-363* declined significantly with age. Centenarians, however, maintained the youthful expression level. This result suggests that miR-363* may be a candidate longevity-associated miRNA.Our comprehensive miRNA data provide a resource for further studies to identify genetic pathways associated with aging and longevity in humans.

    View details for DOI 10.1186/1471-2164-13-353

    View details for Web of Science ID 000315030300001

    View details for PubMedID 22846614

    View details for PubMedCentralID PMC3563618

  • A high-throughput, near-saturating screen for type III effector genes from Pseudomonas syringae PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chang, J. H., Urbach, J. M., Law, T. F., Arnold, L. W., Hu, A., Gombar, S., Grant, S. R., Ausubel, F. M., Dangl, J. L. 2005; 102 (7): 2549-2554


    Pseudomonas syringae strains deliver variable numbers of type III effector proteins into plant cells during infection. These proteins are required for virulence, because strains incapable of delivering them are nonpathogenic. We implemented a whole-genome, high-throughput screen for identifying P. syringae type III effector genes. The screen relied on FACS and an arabinose-inducible hrpL sigma factor to automate the identification and cloning of HrpL-regulated genes. We determined whether candidate genes encode type III effector proteins by creating and testing full-length protein fusions to a reporter called Delta79AvrRpt2 that, when fused to known type III effector proteins, is translocated and elicits a hypersensitive response in leaves of Arabidopsis thaliana expressing the RPS2 plant disease resistance protein. Delta79AvrRpt2 is thus a marker for type III secretion system-dependent translocation, the most critical criterion for defining type III effector proteins. We describe our screen and the collection of type III effector proteins from two pathovars of P. syringae. This stringent functional criteria defined 29 type III proteins from P. syringae pv. tomato, and 19 from P. syringae pv. phaseolicola race 6. Our data provide full functional annotation of the hrpL-dependent type III effector suites from two sequenced P. syringae pathovars and show that type III effector protein suites are highly variable in this pathogen, presumably reflecting the evolutionary selection imposed by the various host plants.

    View details for DOI 10.1073/pnas.0409660102

    View details for Web of Science ID 000227073100055

    View details for PubMedID 15701698

    View details for PubMedCentralID PMC549004