Cost of managing severe cutaneous adverse drug reactions to first-line tuberculosis therapy in South Africa.

OBJECTIVE: To compare the cost of managing treatment-limiting cutaneous adverse drug reactions (CADRs) to first-line anti-tuberculosis drugs to an alternative strategy of immediate treatment initiation using second-line drugs in a South African setting. METHODS: Clinical and cost data were retrospectively collected from patients presenting with a first-line anti-tuberculosis therapy-associated CADR. Costs (2016 US$) were estimated using an ingredient's approach from a healthcare provider perspective. The per-patient and total cost of drug rechallenge, the current management strategy for severe CADR, was calculated. Alternative strategies involving second-line treatment were derived from literature and expert clinical advice. RESULTS: Drug rechallenge costs US $5831 (95% CI: 5134-6527) per patient. Hospitalisation accounted for 62% of this cost. Alternative CADR management strategies using regimens containing rifabutin, bedaquiline and/or delamanid cost 44%-55% less than drug rechallenge (US $2651-US $3276/patient). In univariate sensitivity analyses, drug rechallenge and alternative strategies were most sensitive to hospitalisation and tuberculosis drug costs, respectively. CONCLUSION: Cutaneous adverse drug reactions to anti-tuberculosis treatment represent a significant economic burden. An alternate strategy of outpatient-initiated second-line therapy is economically feasible but requires clinical validation to assess effectiveness.

OBJECTIF: Comparer le coût de la prise ne charge des effets indésirables cutanés (EIC) limitant le traitement aux antituberculeux de première ligne à celui d'une stratégie alternative d'initiation immédiate du traitement par des médicaments de deuxième ligne dans un contexte sud-africain. MÉTHODES: Les données cliniques et les coûts ont été collectés rétrospectivement chez des patients présentant un EIC associé au traitement antituberculeux de première ligne. Les coûts (USD, 2016) ont été estimés en utilisant une approche d'ingrédient du point de vue d'un prestataire de soins de santé. Le coût par patient et le coût total du nouveau traitement, de la stratégie actuelle de prise en charge des cas d'EIC sévère, ont été calculés. Des stratégies alternatives impliquant un traitement de deuxième ligne ont été dérivées de la littérature et de conseils cliniques d'experts. RÉSULTATS: Le coût du nouveau traitement était de 5.831 USD (IC95%: 5.134 - 6.527) par patient. L'hospitalisation représentait 62% de ce coût. Les stratégies alternatives de prise en charge des EIC utilisant des schémas thérapeutiques contenant de la rifabutine, de la bédaquiline et/ou du delamanide coûtent de 44 % à 55 % moins cher que le nouveau traitement (2.651 USD - 3.276 USD/patient). Dans les analyses de sensibilité univariées, les stratégies de re-traitement et les stratégies alternatives étaient plus sensibles aux coûts d'hospitalisation et de médicaments antituberculeux, respectivement. CONCLUSION: Les EIC des antituberculeux représentent une charge économique importante. Une stratégie alternative de traitement de deuxième ligne mise en place chez des patients ambulatoires est économiquement réalisable mais nécessite une validation clinique pour évaluer l'efficacité.

In Vivo Molecular Dissection of the Effects of HIV-1 in Active Tuberculosis.

Increased risk of tuberculosis (TB) associated with HIV-1 infection is primarily attributed to deficient T helper (Th)1 immune responses, but most people with active TB have robust Th1 responses, indicating that these are not sufficient to protect against disease. Recent findings suggest that favourable outcomes following Mycobacterium tuberculosis infection arise from finely balanced inflammatory and regulatory pathways, achieving pathogen control without immunopathology. We hypothesised that HIV-1 and antiretroviral therapy (ART) exert widespread changes to cell mediated immunity, which may compromise the optimal host protective response to TB and provide novel insights into the correlates of immune protection and pathogenesis. We sought to define these effects in patients with active TB by transcriptional profiling of tuberculin skin tests (TST) to make comprehensive molecular level assessments of in vivo human immune responses at the site of a standardised mycobacterial challenge. We showed that the TST transcriptome accurately reflects the molecular pathology at the site of human pulmonary TB, and used this approach to investigate immune dysregulation in HIV-1/TB co-infected patients with distinct clinical phenotypes associated with TST reactivity or anergy and unmasking TB immune reconstitution inflammatory syndrome (IRIS) after initiation of ART. HIV-1 infected patients with positive TSTs exhibited preserved Th1 responses but deficient immunoregulatory IL10-inducible responses. Those with clinically negative TSTs revealed profound anergy of innate as well as adaptive immune responses, except for preservation of type 1 interferon activity, implicated in impaired anti-mycobacterial immunity. Patients with unmasking TB IRIS showed recovery of Th1 immunity to normal levels, but exaggerated Th2-associated responses specifically. These mechanisms of immune dysregulation were localised to the tissue microenvironment and not evident in peripheral blood. TST molecular profiling categorised different mechanisms of immunological dysfunction in HIV-1 infection beyond the effects on CD4 T cells, each associated with increased risk of TB disease and amenable to host-directed therapies.

Lack of cross-toxicity between isoniazid and ethionamide in severe cutaneous adverse drug reactions: a series of 25 consecutive confirmed cases.

BACKGROUND: Isoniazid and ethionamide are important first- and second-line anti-TB drugs (FLDs and SLDs), respectively. Ethionamide is a structural analogue of isoniazid and the two drugs share other similarities, including their metabolism, therapeutic targets, hepato-toxicity patterns and drug resistance. As a result, there has always been concern about possible cross-reactivity between them. METHODS: Among 69 patients with drug rash with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) to FLDs, FLDs were stopped and SLDs added when the skin and laboratory parameters had settled. This was followed by sequential and additive rechallenge with FLDs. We report 25 consecutive cases that developed confirmed cutaneous adverse drug reactions (CADRs) to isoniazid or ethionamide used as FLD and SLD, respectively. RESULTS: Sixty-nine participants who developed CADRs on FLDs were enrolled in the study. Twenty developed a rechallenge reaction to isoniazid and five reacted to ethionamide. Four of the 20 isoniazid cases were patch test positive, 3/20 were skin prick test positive and 13/20 reacted to oral rechallenge. All seven cases that were patch and skin prick test positive were associated with systemic reactions. Twenty of the 25 cases had DRESS and 5 had SJS/TEN. Twenty-three of the 25 cases with rechallenge reactions were HIV infected. Importantly, none of the cases that reacted to ethionamide during the rechallenge reacted to isoniazid and none who subsequently reacted to isoniazid reacted to ethionamide. CONCLUSIONS: Our findings strongly suggest that the risk of cross-reactivity of isoniazid and ethionamide in DRESS syndrome and SJS/TEN is low. These findings have implications for clinical management.

Advanced human immunodeficiency virus (HIV) does not affect ability to utilize lymphadenopathy in assessment of drug reaction with eosinophilia and systemic symptoms syndrome in HIV and tuberculosis: Prospective comparative study.

Background: RegiSCAR validation criteria for drug reaction with eosinophilia and systemic symptoms (DRESS) includes lymphadenopathy, a frequent feature of both tuberculosis (TB) and human immunodeficiency virus (HIV). TB is the most common HIV-associated coinfection. Advanced HIV is associated with lymph node (LN) fibrosis. It is not clear if this negatively affects case validation in HIV-associated DRESS. To answer this question, we designed a prospective descriptive study to assess lymphadenopathy in various combinations of comorbid HIV, TB, and DRESS. Objectives: We sought to describe the prevalence of DRESS-associated lymphadenopathy and characterize LN quality, size, and distribution in a high HIV-TB burden setting over time. Methods: We prospectively and systematically examined LN in 25 consecutive acute DRESS cases hospitalized at a South African tertiary-care center and 10 hospitalized non-DRESS HIV-TB coinfected controls. Results: Fourteen (56%) of 25 patients were HIV infected, with a median (interquartile range) CD4 count of 254 (66-478) cells/mm³, and 7 of 14 were coinfected with TB. Using RegiSCAR criteria, 12 (46%) of 25 were definite DRESS cases, 8 (31%) of 25 probable, and 5 (23%) of 25 possible. Possible cases were excluded in the analysis. Fifteen (75%) of 20 subjects had LN in ≥2 anatomic sites, including all 7 patients with HIV-TB coinfection. In contrast, 1 (20%) of 5 hospitalized non-DRESS HIV-TB coinfected controls had LN. Cervical LN, in 15 (88%) of 17, was most common, followed by axillary (76%) and inguinal (59%). Cervical LN ranged between 1 and 2 cm in size. Among the 8 (32%) of 25 subjects with follow-up data, LN had regressed in all within 6 weeks of stopping the offending drug and initiating TB treatment. There was no correlation with CD4 cell count and LN. Conclusion: Lymphadenopathy is a common feature of acute DRESS, even among HIV-TB-coinfected patients with advanced immunosuppression.

Comment on: Proposal for a new diagnostic classification of photodistributed Stevens-Johnson syndrome and toxic epidermal necrolysis.

Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and SJS/TEN overlap (SJS/TEN), collectively referred to SJS/TEN, form a spectrum of severe life-threatening adverse drug reactions whose pathomechanism is not fully understood. The article "Photodistributed Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis: A Systematic Review and Proposal for a New Diagnostic Classification" by McKinley et. al., discusses a distinct distribution of epidermal necrosis in SJS/TEN, attributable to preceding exposure to ultraviolet radiation (UVR), and relative sparing of photo-protected areas. After reviewing numerous cases within the Immune-mediated Adverse drug Reactions in African HIV endemic setting Register and Biorepository (IMARI-SA) at the University of Cape Town with a similar clinical pattern as those published by McKinley et. al., we propose that the relative sparing of some areas giving an impression of photo-distribution is due to localised increase in skin pressure that reduces the blood supply in that area below a critical threshold. A dip in blood supply below this critical threshold quantitively limited T lymphocytes and cytokines that drive SJS/TEN to reach and damage the skin.

Multiomic single-cell sequencing defines tissue-specific responses in Stevens-Johnson Syndrome and Toxic epidermal necrolysis.

Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) is a rare but life-threatening cutaneous drug reaction mediated by human leukocyte antigen (HLA) class I-restricted CD8+ T-cells. To obtain an unbiased assessment of SJS/TEN cellular immunopathogenesis, we performed single-cell (sc) transcriptome, surface proteome, and TCR sequencing on unaffected skin, affected skin, and blister fluid from 17 SJS/TEN patients. From 119,784 total cells, we identified 16 scRNA-defined subsets, confirmed by subset-defining surface protein expression. Keratinocytes upregulated HLA and IFN-response genes in the affected skin. Cytotoxic CD8+ T-cell subpopulations of expanded and unexpanded TCRαß clonotypes were shared in affected skin and blister fluid but absent or unexpanded in SJS/TEN unaffected skin. SJS/TEN blister fluid is a rich reservoir of oligoclonal CD8+ T-cells with an effector phenotype driving SJS/TEN pathogenesis. This multiomic database will act as the basis to define antigen-reactivity, HLA restriction, and signatures of drug-antigen-reactive T-cell clonotypes at a tissue level.

Management of Adult Patients With Drug Reaction With Eosinophilia and Systemic Symptoms: A Delphi-Based International Consensus.

Importance: Drug reaction with eosinophilia and systemic symptoms (DRESS) is a rare but potentially fatal drug hypersensitivity reaction. To our knowledge, there is no international consensus on its severity assessment and treatment. Objective: To reach an international, Delphi-based multinational expert consensus on the diagnostic workup, severity assessment, and treatment of patients with DRESS. Design, Setting, and Participants: The Delphi method was used to assess 100 statements related to baseline workup, evaluation of severity, acute phase, and postacute management of DRESS. Fifty-seven international experts in DRESS were invited, and 54 participated in the survey, which took place from July to September 2022. Main Outcomes/Measures: The degree of agreement was calculated with the RAND-UCLA Appropriateness Method. Consensus was defined as a statement with a median appropriateness value of 7 or higher (appropriate) and a disagreement index of lower than 1. Results: In the first Delphi round, consensus was reached on 82 statements. Thirteen statements were revised and assessed in a second round. A consensus was reached for 93 statements overall. The experts agreed on a set of basic diagnostic workup procedures as well as severity- and organ-specific further investigations. They reached a consensus on severity assessment (mild, moderate, and severe) based on the extent of liver, kidney, and blood involvement and the damage of other organs. The panel agreed on the main lines of DRESS management according to these severity grades. General recommendations were generated on the postacute phase follow-up of patients with DRESS and the allergological workup. Conclusions and Relevance: This Delphi exercise represents, to our knowledge, the first international expert consensus on diagnostic workup, severity assessment, and management of DRESS. This should support clinicians in the diagnosis and management of DRESS and constitute the basis for development of future guidelines.

Annular erythema and photosensitivity as manifestations of efavirenz-induced cutaneous reactions: a review of five consecutive cases.

OBJECTIVES: In HIV-infected persons, a rash is the most common manifestation of drug hypersensitivity reactions. Non-nucleotide reverse transcriptase inhibitors are a major cause of cutaneous reactions. While the characteristics of nevirapine-associated cutaneous adverse drug reactions (CADRs) have been well described, there are limited data on efavirenz-associated CADRs. The objective of this study was to characterize the clinical features of consecutive cases of efavirenz-associated CADRs in a single referral centre diagnosed over a 3 year period. METHODS: We retrospectively reviewed the clinical records of 231 patients admitted with CADRs to a tertiary dermatology ward in Cape Town, South Africa. RESULTS: In 42/231(18%) cases, there had been exposure to efavirenz in the preceding 8 weeks. Of these, 5/42 (12%) patients were diagnosed with probable efavirenz-associated CADRs based on the Naranjo score. The median exposure to efavirenz before the onset of the rash was 12 days (range 2-48). All the patients were female, with a median age of 31 years and a median CD4 cell count of 300 cells/mm(3) (range 81-887). Four had a photo-distributed eruption and one had a confluent indurated erythema affecting the face, trunk and limbs. In three out of five cases, there were annular plaques with raised erythematous edges and dusky centres, which were photo-distributed. Two patients had a mild transaminitis and another a mild eosinophilia. Histological features were non-specific, with perivascular lymphocytes the only consistent feature. In all five cases, efavirenz was withdrawn and potent topical steroid was the only CADR-specific intervention. The eruptions resolved on discharge from hospital, with no sequelae except for residual post-inflammatory hyperpigmentation. CONCLUSIONS: Photo-distribution and annular erythema should alert clinicians to the possibility of efavirenz-associated CADRs.

Updates in SJS/TEN: collaboration, innovation, and community.

Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN) is a predominantly drug-induced disease, with a mortality rate of 15-20%, that engages the expertise of multiple disciplines: dermatology, allergy, immunology, clinical pharmacology, burn surgery, ophthalmology, urogynecology, and psychiatry. SJS/TEN has an incidence of 1-5/million persons per year in the United States, with even higher rates globally. One of the challenges of SJS/TEN has been developing the research infrastructure and coordination to answer questions capable of transforming clinical care and leading to improved patient outcomes. SJS/TEN 2021, the third research meeting of its kind, was held as a virtual meeting on August 28-29, 2021. The meeting brought together 428 international scientists, in addition to a community of 140 SJS/TEN survivors and family members. The goal of the meeting was to brainstorm strategies to support the continued growth of an international SJS/TEN research network, bridging science and the community. The community workshop section of the meeting focused on eight primary themes: mental health, eye care, SJS/TEN in children, non-drug induced SJS/TEN, long-term health complications, new advances in mechanisms and basic science, managing long-term scarring, considerations for skin of color, and COVID-19 vaccines. The meeting featured several important updates and identified areas of unmet research and clinical need that will be highlighted in this white paper.

Transcriptional profiling of innate and adaptive human immune responses to mycobacteria in the tuberculin skin test.

The tuberculin skin test (TST) is a model of integrated innate and adaptive human immune responses to Mycobacterium tuberculosis, but the component processes that are involved in this model have not previously been defined in vivo. We used transcriptional profiling to study these responses within the TST at molecular and system levels. Skin biopsies from TST injection sites were examined in subjects classified as TST(+) or TST(-) by clinical and histological criteria. Genome-wide expression arrays showed evolution of immune responses reflecting T-cell activation and recruitment with uniquely Th1-polarized responses and cytotoxic T cells (CTLs). In addition, distinct innate immune and IFN-γ-stimulated gene expression signatures were identified, under the regulation of NF-κB and STAT1 transcriptional control. These were highly enriched for chemokines and MHC class II molecules providing a potential mechanism for paracrine amplification of inflammatory responses in the TST, by supporting cellular recruitment and enhancing antigen presentation. The same repertoire of innate and adaptive immune responses was evident in TST(+) and TST(-) subjects alike, clinically positive TSTs being distinguished only by quantitatively greater differences. These data provide new insights into complex multifaceted responses within the TST, with much greater sensitivity than previous clinical or histological assessments.

Disease severity and status in Stevens-Johnson syndrome and toxic epidermal necrolysis: Key knowledge gaps and research needs.

Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are on a spectrum of cutaneous drug reactions characterized by pan-epidermal necrosis with SJS affecting < 10% of body surface area (BSA), TEN > 30%, and SJS/TEN overlap between 10 and 30%. Severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is a validated tool to predict mortality rates based on age, heart rate, BSA, malignancy and serum urea, bicarbonate, and glucose. Despite improved understanding, SJS/TEN mortality remains constant and therapeutic interventions are not universally accepted for a number of reasons, including rarity of SJS/TEN; inconsistent definition of cases, disease severity, and endpoints in studies; low efficacy of interventions; and variations in treatment protocols. Apart from mortality, none of the other endpoints used to evaluate interventions, including duration of hospitalization, is sufficiently standardized to be reproducible across cases and treatment centers. Some of the gaps in SJS/TEN research can be narrowed through international collaboration to harmonize research endpoints. A case is made for an urgent international collaborative effort to develop consensus on definitions of endpoints such as disease status, progression, cessation, and complete re-epithelialization in interventional studies. The deficiencies of using BSA as the sole determinant of SJS/TEN severity, excluding internal organ involvement and extension of skin necrosis beyond the epidermis, are discussed and the role these factors play on time to healing and mortality beyond the acute stage is highlighted. The potential role of artificial intelligence, biomarkers, and PET/CT scan with radiolabeled glucose as markers of disease status, activity, and therapeutic response is also discussed.

Recognizing Drug Hypersensitivity in Pigmented Skin.

The imagery of pigmented skin is underrepresented in teaching materials such as textbooks, journals, and online references, and this has resulted in poorer diagnostic and management outcomes of skin pathology, including delayed cutaneous drug hypersensitivity reactions. In this review, we use clinical images to highlight factors that impact clinical presentations and sequelae of drug hypersensitivity reactions in pigmented skin compared with nonpigmented skin. We describe clinical features in some anatomic sites that aid diagnosis or are associated with more severe sequelae. Finally, we discuss strategies that may aid the diagnosis and management of these reactions in pigmented skin.

Delabeling Delayed Drug Hypersensitivity: How Far Can You Safely Go?

Delayed immune-mediated adverse drug reactions (IM-ADRs) are defined as reactions occurring more than 6 hours after dosing. They include heterogeneous clinical phenotypes that are typically T-cell-mediated reactions with distinct mechanisms across a wide spectrum of severity from benign exanthems through to life-threatening cutaneous or organ-specific diseases. For mild reactions such as benign exanthem, considerations for delabeling are similar to immediate reactions and may include a graded or single-dose drug challenge with or without preceding skin or patch testing. Evaluation of challenging cases such as the patient who is on multiple drugs at the time a severe delayed IM-ADR occurs should prioritize clinical ascertainment of the most likely phenotype and implicated drug(s). Although not widely available and validated, procedures such as patch testing, delayed intradermal skin testing, and laboratory-based functional drug assays or genetic (human leukocyte antigen) testing may provide valuable information to further help risk stratify patients and identify the likely implicated and/or cross-reactive drug(s). The decision to use a drug challenge as a diagnostic or delabeling tool in a patient with a severe delayed IM-ADR should weigh the risk-benefit ratio, balancing the severity and priority for the treatment of the underlying, and the availability of alternative efficacious and safe treatments.

SJS/TEN 2019: From science to translation.

Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are potentially life-threatening, immune-mediated adverse reactions characterized by widespread erythema, epidermal necrosis, and detachment of skin and mucosa. Efforts to grow and develop functional international collaborations and a multidisciplinary interactive network focusing on SJS/TEN as an uncommon but high burden disease will be necessary to improve efforts in prevention, early diagnosis and improved acute and long-term management. SJS/TEN 2019: From Science to Translation was a 1.5-day scientific program held April 26-27, 2019, in Vancouver, Canada. The meeting successfully engaged clinicians, researchers, and patients and conducted many productive discussions on research and patient care needs.

Drug hypersensitivity in HIV infection.

PURPOSE OF REVIEW: Immune-mediated adverse drug reactions (IM-ADRs) are many times more common in HIV-infected patients. Usual offending drugs include antiretroviral and antiinfectives, but the burden of specific drug IM-ADRs is population-specific; changing as new and fixed dose combinations enter the market, and drug-resistance patterns demand. This review considers recent literature on epidemiology, mechanisms, clinical management and prevention of IM-ADRs amongst persons living with HIV/AIDS. RECENT FINDINGS: Epidemiological studies continue to describe high rates of delayed hypersensitivity to known offenders, as well as similar reactions in preexposure prophylaxis. IM-ADRs to oral and injectable integrase strand transfer inhibitors are reported with expanding use. The clinical spectrum and management of IM-ADRs occurring in HIV-infected populations is similar to uninfected; with exceptions such as a recently described severe delayed efavirenz DILI with high mortality. Furthermore, the context can be unique, such as the lower than expected mortality in a Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) cohort from a HIV/TB high burden setting. Programmatic data showing the near complete elimination of Abacavir drug hypersensitivity syndrome following implementation of HLA-B57:01 screening is a stellar example of how prevention is possible with mechanistic insight. SUMMARY: IM-ADRs remain a challenge in persons living with HIV. The complexities posed by polypharmacy, overlapping drug toxicities, drug interactions, overlap of IM-ADRs with other diseases, limited alternative drugs, and vulnerable patients with advanced immunosuppression with high mortality, necessitate increased use of drug provocation testing, treat-through and desensitization strategies. There is an urgent need for improved diagnostics and predictive biomarkers for prevention, or to guide treat-through, rechallenge and desensitization approaches.

SJS/TEN 2017: Building Multidisciplinary Networks to Drive Science and Translation.

Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) is a life-threatening, immunologically mediated, and usually drug-induced disease with a high burden to individuals, their families, and society with an annual incidence of 1 to 5 per 1,000,000. To effect significant reduction in short- and long-term morbidity and mortality, and advance clinical care and research, coordination of multiple medical, surgical, behavioral, and basic scientific disciplines is required. On March 2, 2017, an investigator-driven meeting was held immediately before the American Academy of Dermatology Annual meeting for the central purpose of assembling, for the first time in the United States, clinicians and scientists from multiple disciplines involved in SJS/TEN clinical care and basic science research. As a product of this meeting, this article summarizes the current state of knowledge and expert opinion related to SJS/TEN covering a broad spectrum of topics including epidemiology and pharmacogenomic networks; clinical management and complications; special populations such as pediatrics, the elderly, and pregnant women; regulatory issues and the electronic health record; new agents that cause SJS/TEN; pharmacogenomics and immunopathogenesis; and the patient perspective. Goals include the maintenance of a durable and productive multidisciplinary network that will significantly further scientific progress and translation into prevention, early diagnosis, and management of SJS/TEN.

Impact of correcting the lymphocyte count to improve the sensitivity of TB antigen-specific peripheral blood-based quantitative T cell assays (T-SPOT.(®)TB and QFT-GIT).

BACKGROUND: The standardized blood-based TB antigen-specific T cell assay, T-SPOT.(®)TB, is ~10% more sensitive than QuantiFERON(®)-TB-GIT (QFT-GIT) in detecting presumed latent TB infection (LTBI). Whilst T-SPOT.(®)TB uses a fixed number of lymphocytes per well, QFT-GIT uses a fixed volume of blood (~1 mL). However, the person-to-person lymphocyte count can vary by 2 to 3 fold. We hypothesized that this variability could explain the reduced sensitivity of QFT-GIT. The findings could have potential implications for improving case detection. METHODS: T-SPOT.(®)TB was compared to QFT-GIT readouts before and after normalization of lymphocyte count (by adjusting the blood volume or lymphocyte enrichment within a fixed 1 mL volume) to an arbitrary value of 2.5×10(6) cells/mL. Within-test variability was evaluated to meaningfully interpret results. RESULTS: In patient-specific optimization experiments IFN-γ concentrations significantly increased when QFT-GIT positive samples were enriched with increasing concentrations of lymphocytes (1×10(6) vs. 2.5×10(6) cells/mL). However, for the group as a whole lymphocyte enrichment whilst maintaining a ~1 mL volume, compared to un-enriched samples, did not significantly increase IFN-γ [median (range): 0.03 (0-4.41) vs. 0.20 (0-2.40) IU/mL; P=0.64]. There was also no increase in IFN-γ readouts when QFT-GIT lymphocyte numbers were corrected (to 2.5×10(6) lymphocytes/mL) using volume adjustment. Interestingly, adjusted values were significantly lower than unadjusted ones [median (range): 0.02 (0-12.93) vs. 0.09 (0-14.23) IU/mL; P=0.008]. CONCLUSIONS: In QFT-GIT negative subjects lymphocyte enrichment did not increase QFT-GIT positivity rates. The reduced clinical sensitivity of the QFT-GIT assay, compared to T-SPOT.(®)TB, is likely to be due to factors other than lymphocyte count alone. Further studies are required to clarify these findings.