Additional testing and CXCL9
These tests can help with identifying HLH
Genetic testing takes time, and patients with primary HLH often require immediate treatment to control their hyperinflammation.1 There are a range of other tests that can be conducted in the meantime to help identify potential underlying triggers and to help confirm or rule out a primary HLH diagnosis.
Flow cytometry testing
CD=cluster of differentiation; SLAM=signaling lymphocytic activation molecule; XIAP=X-linked inhibitor of apoptosis.
Flow cytometry for perforin expression and CD107a have high specificity for identifying HLH with a genetic basis.3
Ancillary testing2,4
CMV=cytomegalovirus; CT=computed tomography; EBV=Epstein-Barr virus; HSV=herpes simplex virus; MRI=magnetic resonance imaging; PCR=polymerase chain reaction; PET=positron emission tomography.
These tests can help identify an underlying trigger for patients with primary HLH, or to rule out other conditions.2
Other tests2
ALT=alanine aminotransferase; CXCL9=chemokine (C-X-C motif) ligand 9; IL=interleukin.
These tests are useful for identifying the typical features of primary HLH.5 There is evidence suggesting that CXCL9 testing can be helpful for measuring the IFNγ levels in patients with HLH.6
CXCL9 and IFNγ
CXCL9 is a chemokine (a type of cytokine) released almost exclusively by IFNγ-activated macrophages. The primary function of CXCL9 is to attract T cells into inflamed tissues.6
A retrospective study:
CXCL9 as a novel prognostic marker to identify high-risk adults with hemophagocytic lymphohistiocytosis8
A retrospective, multicenter chart review was conducted to broadly evaluate potential clinical biomarkers, including CXCL9, to determine which combination of markers provides the greatest prognostic utility in a large cohort of individuals undergoing clinical HLH evaluation.
CXCL9 emerged as the only optimal predictor of inpatient mortality among all markers assessed, with risk increasing as CXCL9 levels rose.
Study limitations8
Retrospective design may be impacted by unrecognized confounders. Restricted to patients ≥15 years, limiting generalizability to younger populations. Variability in HLH recognition timing across patients and centers may introduce selection bias. Sensitivity analyses were conducted to mitigate bias.
Inclusion criteria8
Hospitalized patients ≥15 years undergoing HLH evaluation with ≥1 clinically validated CXCL9 test from a Clinical Laboratory Improvement Amendments (CLIA)-certified lab were included. Patients were excluded if CXCL9 testing occurred after initiation of HLH-directed therapy.
Patient characteristics8
171 adult patients were included and categorized as HLH- or HLH+. HLH+ was defined as meeting ≥4/8 HLH-2004 criteria and/or an HScore ≥169. Of 126 HLH+ patients, 73 met ≥5/8 HLH-2004 criteria.*
Key findings for clinical practice8
The authors reported that CXCL9, a surrogate marker for IFNγ, served as a novel and consistent clinical laboratory marker in the identification and prognosis of adults presenting with HLH.*
Elevated CXCL9 levels were associated with early mortality in HLH+ patients
Strength of association and mortality risk
In patients with HLH, CXCL9 emerged as the only optimal prognostic marker of inpatient mortality across all evaluated labs, with elevated levels significantly associated with early mortality.8
Increasing risk
Higher baseline CXCL9 levels were associated with progressively higher mortality risk, further supporting the strength of its prognostic utility.3
Decreased levels in survivors
Among patients with serial measurements, significant decreases in CXCL9 levels were observed more frequently in 90-day survivors.8
*Patients in the HLH+ cohort met at least 4 out of 8 HLH-2004 criteria and/or had an HScore ≥169. A cutoff of 4 out of 8 HLH-2004 criteria was used to capture a broad population including early HLH presentations and/or similar IFNγ-driven hyperinflammatory syndromes of which HLH represents the most severe manifestation. This modified cutoff also helped control for bone marrow biopsies not being routinely performed and a recent study suggested similar sensitivity when compared to the original cutoff.
Serial monitoring of absolute CXCL9 levels and their trajectory may help physicians evaluate the risk of mortality in patients with HLH.8
CXCL9 testing sites
cincinnatichildrens/Tests/723501
cxcl9-level
This is not an exhaustive list of labs offering CXCL9 testing, as additional labs continue to build new capabilities. Please check for the availability of this test within your own institution prior to contacting these sites.
References: 1. Jordan MB, Allen CE, Weitzman S, Filipovich AH, McClain KL. How I treat hemophagocytic lymphohistiocytosis. Blood. 2011;118(15):4041-4052. doi:10.1182/blood-2011-03-278127 2. Cincinnati Children’s Diagnosing HLH. Accessed October 23, 2023. https://www.cincinnatichildrens.org/service/h/hlh/clinical/test 3. Marsh RA, Haddad E. How I treat primary haemophagocytic lymphohistiocytosis. Br J Haematol. 2018;182(2):185-199. doi:10.1111/bjh.15274 4. Jongbloed EM, Hermans MAW, Wabbijn M, van Kampen JJA, van Laar JAM. HLH caused by an HSV-2 infection: a case report and review of the literature. Neth J Med. 2020;78(5):282-285. 5. Jordan MB, Allen CE, Greenberg J, et al. Challenges in the diagnosis of hemophagocytic lymphohistiocytosis: Recommendations from the North American Consortium for Histiocytosis (NACHO). Pediatr Blood Cancer. 2019;66(11):e27929. doi:10.1002/pbc.27929 6. Sylvest S. From the Clinical Laboratories of the Cancer & Blood Diseases Institute. Cincinnati Children’s Hospital. Winter 2019;(15):1-4. 7. De Benedetti F, Prencipe G, Bracaglia C, Marasco E, Grom AA. Targeting interferon-γ in hyperinflammation: opportunities and challenges. Nat Rev Rheumatol. 2021;17(11):678-691. doi:10.1038/s41584-021-00694-z 8. Rocco JM, Oved JH, Patel RJ, et al. CXCL9 as a novel prognostic marker to identify high-risk adults with hemophagocytic lymphohistiocytosis. Blood. 2026;147(9):960-972. doi:10.1182/blood.2025030976
