The letter, authored by Barina Khan of Karachi Medical and Dental College and published on 3 September 2026 as Volume 29, article number 59 of the journal, is written in direct response to a pilot study by Tran and colleagues that documented dynamic platelet dysfunction in patients undergoing extracorporeal membrane oxygenation. That pilot work, which appeared in the same journal earlier in 2026, used platelet function testing to follow how platelet performance changed over the course of ECMO support and explored whether those changes tracked with clinically significant bleeding. The new letter does not dispute that platelet dysfunction is real and important in ECMO patients. Instead, it questions whether the specific instrument and protocol used can reliably detect it in this population.

The core of the concern lies in what laboratory scientists call a ceiling effect. The PFA-200 measures the time it takes for platelets, under controlled high shear conditions, to form a plug that occludes a microscopic aperture in a cartridge coated with platelet agonists such as collagen and epinephrine or collagen and adenosine diphosphate. When platelet function is severely impaired, the plug simply never forms, and the instrument reports a result at or above the maximum assay limit, typically a value greater than 300 seconds. In profoundly thrombocytopenic or platelet-exhausted patients, which many ECMO patients quickly become, large numbers of test results pile up at this artificial ceiling. Once a value has been censored at the upper limit, the assay can no longer distinguish between moderately severe and catastrophic platelet failure, compressing exactly the range of dysfunction that matters most for predicting bleeding.

Khan’s letter argues that this censoring problem is particularly acute during ECMO, where platelet counts fall progressively, platelets become activated and exhausted through continuous contact with the oxygenator membrane and circuit tubing, and acquired platelet defects accumulate over days of support. If a study correlates closure times with bleeding episodes in such a cohort, the relationship may be flattened or distorted by the many results that read simply as greater than 300 seconds. Statistical associations computed on censored data risk either underestimating the true strength of the link between platelet failure and hemorrhage or, depending on how the ceiling values are handled in the analysis, producing misleading conclusions about when platelet dysfunction begins to matter clinically.

The second confounder the letter highlights is hematocrit, the proportion of blood volume occupied by red blood cells. It is a long-standing observation in hematology that the PFA-100 and PFA-200 are exquisitely sensitive to the hematocrit of the sample. Red cells are not passive bystanders in primary hemostasis; they physically push platelets toward the vessel wall in flowing blood and contribute chemical signals, including adenosine diphosphate released from erythrocytes, that amplify platelet activation. When the hematocrit drops below roughly 30 percent, closure times lengthen even if platelets themselves are functioning normally, and severe anemia can push closure times beyond the assay limit on its own. Conversely, elevating the hematocrit can shorten closure times and mask genuine platelet defects, an effect documented decades ago in studies of uremic and cirrhotic patients evaluated on the platelet function analyzer.

This sensitivity is a serious problem in the ECMO population specifically. Patients on extracorporeal support are frequently anemic, whether from hemodilution caused by circuit priming, hemolysis within the circuit, repeated blood sampling, gastrointestinal bleeding, or the suppressed red cell production that accompanies critical illness. In such patients, a prolonged closure time may reflect the red cell deficit rather than intrinsic platelet failure, and the degree of prolongation may bear little relationship to the true functional capacity of the platelets. Khan’s letter suggests that unless hematocrit is either matched across study groups or formally adjusted for in the statistical model, the association reported between PFA-200 closure times and bleeding in ECMO patients may be confounded from the outset, with anemia masquerading as platelet dysfunction.

The letter places these concerns in a broader and somewhat sobering context. The clinical utility of closure times on the platelet function analyzer has been debated for more than two decades. Studies in cardiac surgery patients have repeatedly questioned whether the device predicts blood loss after cardiopulmonary bypass, another setting in which acquired platelet defects, hemodilution and anemia coexist. A comprehensive review in the American Journal of Hematology catalogued the assay’s utility across bleeding disorders while also documenting its susceptibility to hematologic variables, and a worldwide survey of platelet function testing practices conducted under the auspices of the International Society on Thrombosis and Haemostasis underscored how much variability exists in how platelet function is assessed even among expert laboratories. Against that backdrop, applying the PFA-200 to the uniquely harsh environment of extracorporeal circulation demands particular caution about the assay’s known limitations.

None of this means the assay should be abandoned in the ECMO setting, the letter’s argument implies, but rather that its results must be interpreted with an awareness of when the instrument can and cannot see. Practical strategies exist. Researchers can report the proportion of censored results explicitly and use statistical methods designed for data with detection limits rather than treating the ceiling value as a genuine number. Studies can stratify closure times by hematocrit, exclude samples with severe anemia from platelet-focused analyses, or measure closure times only after red cell transfusion has stabilized the hematocrit. Complementary tests that are less dependent on shear, hematocrit and sample handling, such as light transmission aggregometry, flow cytometric markers of platelet activation, or other point-of-care viscoelastic and platelet-mapping devices, can help triangulate the true state of platelet function. The pilot study’s central observation, that platelet dysfunction evolves dynamically during ECMO, remains valuable; the question is whether the PFA-200, as deployed, is measuring that dysfunction or partly measuring the anemia around it.

The stakes are far from academic. Bleeding remains one of the most feared complications of ECMO, occurring in a substantial fraction of patients and driving decisions about anticoagulation intensity, transfusion thresholds and circuit management. If closure times on the PFA-200 are adopted as a bedside guide without accounting for ceiling effects and hematocrit, clinicians risk both false reassurance, when an apparently normal result is actually capped by the assay limit in a patient with profound platelet exhaustion, and false alarm, when a prolonged result in an anemic patient triggers unnecessary platelet transfusion. Given that platelet transfusions carry their own risks, including allergic reactions, transfusion-associated circulatory overload and the theoretical promotion of thrombosis in a patient group already prone to circuit clotting, refining which patients truly need platelet support is a matter of real clinical consequence.

Khan’s letter is a compact methodological intervention, but it lands at a moment when interest in platelet function testing during extracorporeal support is growing rapidly. As devices for measuring closure times, aggregometry and platelet activation migrate from hematology laboratories to the intensive care unit bedside, the letter serves as a reminder that the validity of any such measurement depends on the biology of the sample as much as the precision of the instrument. In ECMO patients, where thrombocytopenia, platelet exhaustion and anemia march together, closure times must be read with both eyes open. Whether future studies can confirm a robust, hematocrit-independent association between PFA-200 results and bleeding in this population will determine whether the assay earns a genuine place in the ECMO management toolkit, or remains a test whose ceiling it cannot see above and whose red cell context it cannot escape.

Subject of Research: The reliability of PFA-200 platelet function closure times for assessing bleeding risk during extracorporeal membrane oxygenation

Article Title: PFA-200 closure times in ECMO: Are ceiling effects and hematocrit confounding the bleeding association?

Article References: Khan, B. (2026). PFA-200 closure times in ECMO: Are ceiling effects and hematocrit confounding the bleeding association?. Journal of Artificial Organs, 29(4), Article 59. https://doi.org/10.1007/s10047-026-01589-0

Image Credits: AI Generated

DOI: 10.1007/s10047-026-01589-0

Keywords: ECMO, PFA-200, platelet function, closure time, bleeding risk, hematocrit, coagulation, extracorporeal membrane oxygenation, platelet dysfunction, anemia, point-of-care testing, Journal of Artificial Organs

Fibrinogen sits at the heart of hemostasis. When blood vessels are injured, the enzyme thrombin cleaves fibrinogen into fibrin strands, which weave together into the meshwork of a stable clot. When fibrinogen levels fall below roughly 2.0 grams per liter, the threshold the researchers used to define hypofibrinogenemia in this study, that meshwork becomes fragile or fails to form at all, leaving patients exposed to bleeding risks at a time when many are already fighting severe, multidrug-resistant infections. The problem for clinicians has long been that hypofibrinogenemia in intensive care patients has many potential causes, including sepsis itself, disseminated intravascular coagulation, liver dysfunction, and massive transfusion, making it difficult to know when the antibiotic rather than the underlying illness is to blame.

The research team, led by Xiong Guo, Yao Zhang, Tao Yin, and corresponding author Ping Wang, addressed this ambiguity by focusing on the tigecycline trough concentration, the lowest level of the drug in plasma, measured just before the next dose is administered. Trough concentrations are a cornerstone of therapeutic drug monitoring because they capture the baseline exposure a patient carries between doses. Patients treated between January 2018 and May 2026 were enrolled, and every case of hypofibrinogenemia was adjudicated using WHO-UMC causality criteria, a standardized pharmacovigilance framework that helps separate drug-induced adverse events from those attributable to disease processes. Patients were then divided into a hypofibrinogenemia group and a normal group based on their fibrinogen measurements.

Using multivariable logistic regression, a statistical technique that isolates the independent contribution of each factor while controlling for the others, the team identified three independent risk factors for developing the complication: baseline fibrinogen level, duration of tigecycline treatment, and, critically, the trough concentration of the drug itself. Baseline fibrinogen carried a p-value of 0.022, treatment duration a p-value of 0.007, and trough concentration a p-value of 0.026, all of which reached conventional thresholds of statistical significance. Receiver operating characteristic analysis, which evaluates how well a continuous variable discriminates between patients who do and do not experience an outcome, then translated these risk factors into practical clinical cutoffs. Patients with a trough concentration of 0.27 micrograms per milliliter or higher, a treatment duration of 6.50 days or longer, or a baseline fibrinogen below 4.55 grams per liter faced markedly elevated risk.

Perhaps the most striking finding emerged when the investigators sorted patients into quartiles according to their trough concentrations. The incidence of hypofibrinogenemia rose in a clean, stepwise gradient across the quartiles, climbing from 36.11 percent in the lowest quartile to 82.05 percent in the highest, with a p-value for trend below 0.001. This dose-response relationship is exactly the kind of biological signal that lends credibility to a causal association: as exposure to the drug increases, so does the probability of harm, in a predictable and monotonic fashion. For intensive care physicians, the implication is that a simple blood measurement, available through routine therapeutic drug monitoring, could flag patients heading toward a coagulation crisis before fibrinogen levels collapse.

Beyond establishing who is at risk, the study mapped the natural history of the complication in unusual detail. The median time from the start of therapy to the onset of hypofibrinogenemia was 7 days, meaning clinicians should not assume that early uneventful treatment rules the risk out. Once established, the median duration of hypofibrinogenemia was 6 days. Most reassuring, however, was the recovery phase: after tigecycline was discontinued, fibrinogen levels returned to normal within a median of just 2.5 days. This rapid rebound suggests that the drug’s effect on fibrinogen is, at least in most patients, reversible rather than a sign of lasting injury to the synthetic machinery of the liver, which produces the vast majority of circulating fibrinogen.

The correlation analysis revealed an intriguing internal logic to the recovery process. Fibrinogen recovery time after discontinuation of tigecycline was positively correlated with both the time to hypofibrinogenemia onset and the duration of the hypofibrinogenemia episode, with both correlations reaching a p-value of 0.004. In other words, patients whose fibrinogen fell early, and those whose levels remained suppressed for longer, also took longer to bounce back once the drug was withdrawn. This pattern hints at a cumulative exposure phenomenon: the deeper and more prolonged the disruption, the more time the body’s fibrinogen production requires to restore equilibrium. It also reinforces the practical value of early detection, since patients identified and managed before prolonged suppression sets in may recover faster.

Importantly, the researchers also examined whether hypofibrinogenemia translated into worse short-term survival. Using Cox regression, they assessed 30-day mortality and found no significant association between the complication and death within a month, with a p-value of 0.289. That null finding should not be read as license for complacency, the study’s structure suggests, because the enrolled patients were already among the sickest in the hospital, with severe infections caused by multidrug-resistant pathogens, and competing risks in such a population can obscure the specific contribution of any single complication. Nevertheless, the result provides useful context: tigecycline-induced hypofibrinogenemia appears to be a common and monitorable adverse effect whose clinical management can focus on surveillance and timely drug withdrawal rather than panic.

The mechanistic story behind these observations remains an open question, and the authors are careful not to overclaim. Tigecycline is extensively metabolized and cleared through the liver and biliary system, and previous reports have linked the drug to elevations in liver enzymes, bilirubin, and coagulation parameters including prothrombin time and the international normalized ratio. One plausible explanation is that high cumulative exposure interferes directly or indirectly with hepatic fibrinogen synthesis, or with the clotting cascade more broadly, though the precise molecular pathway has not been pinned down. What the new study adds is a quantitative framework: a specific trough concentration threshold, a specific treatment duration, and a specific baseline fibrinogen level that together allow clinicians to stratify risk before the complication develops.

For the growing field of therapeutic drug monitoring in critical care, the findings carry a broader message. Antibiotics are often dosed by standard weight-based formulas that ignore the enormous pharmacokinetic variability among critically ill patients, whose organ function, fluid status, and protein binding can swing dramatically from day to day. Tigecycline, despite its approval and widespread use against serious Gram-positive and Gram-negative infections, has no well-established therapeutic range for safety, and this study suggests that establishing one could prevent a substantial burden of harm. The work was supported by the Hunan Natural Science Foundation, and the team notes that the risk gradient across concentration quartiles was prominent and progressive. If future prospective studies confirm the cutoffs identified here, routine trough measurement could become as standard a part of tigecycline therapy as the drug’s acclaimed antimicrobial coverage, turning an invisible pharmacokinetic variable into an actionable shield for patients who have little physiological reserve left to spare.

One reason trough monitoring may be especially informative for tigecycline lies in the drug’s unusual pharmacokinetic profile. Unlike most antibiotics, tigecycline distributes extensively into tissues, yielding a large volume of distribution and plasma concentrations that are only a small fraction of total body exposure. Critically ill patients are notoriously variable in this regard: shifts in fluid balance, hypoalbuminemia, hepatic congestion, and evolving organ dysfunction can all reshape how the drug behaves in a given individual, so two patients receiving the same weight-based dose may carry very different internal exposures. A trough measurement offers a practical window into that variability at the bedside.

The choice of a 2.0 grams per liter fibrinogen threshold also deserves comment. Fibrinogen is an acute-phase reactant, meaning it typically rises during inflammation, so many patients with severe infections start therapy with elevated levels. This may explain why a baseline value below 4.55 grams per liter emerged as a risk factor: patients whose fibrinogen reserves are already modest have less buffer before drug-related suppression pushes them into the hypofibrinogenemic range. It also complicates interpretation, since a falling fibrinogen in an inflamed patient may still represent a meaningful decline even if the absolute value remains above conventional cutoffs.

As a retrospective, single-center analysis, the study has inherent limitations that temper broad generalization. Concentration measurements were obtained as part of routine care rather than a standardized sampling protocol, and unmeasured confounders such as concurrent transfusions, blood products, or other fibrinogen-lowering drugs cannot be fully excluded. The authors’ use of WHO-UMC adjudication mitigates but does not eliminate this concern. Nevertheless, the open-access dataset, the dose-response gradient, and the internally consistent timing relationships provide a solid foundation for the prospective validation studies that would be needed before the proposed cutoffs enter routine clinical practice.

Subject of Research: The association between tigecycline trough plasma concentration and tigecycline-induced hypofibrinogenemia in critically ill patients.

Article Title: Tigecycline trough concentration and its relationship with hypofibrinogenemia: from onset and duration to recovery

Article References: Guo, X., Zhang, Y., Yin, T., & Wang, P. (2026). Tigecycline trough concentration and its relationship with hypofibrinogenemia: from onset and duration to recovery. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14419-8

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14419-8

Keywords: tigecycline, hypofibrinogenemia, trough concentration, therapeutic drug monitoring, fibrinogen, intensive care unit, antibiotic adverse effects, coagulation, multidrug-resistant infections, pharmacokinetics, drug safety, BMC Infectious Diseases

The clinical logic behind platelet-rich plasma, commonly abbreviated PRP, is deceptively simple. Platelets are the blood’s first responders, streaming to sites of injury and releasing a cocktail of growth factors and signaling proteins that orchestrate clotting, inflammation resolution, and tissue rebuilding. By concentrating platelets from a patient’s blood and re-delivering them to a damaged site, clinicians aim to amplify the body’s own repair mechanisms. Because the material is autologous, derived from the patient, it sidesteps immune rejection and disease transmission concerns that complicate donor-derived products. But aging is known to blunt tissue regeneration, raising an uncomfortable question: if regeneration slows with age, does the PRP made from an 80-year-old’s blood still carry the molecular machinery needed to heal?

That is precisely the question addressed by Anna Buisan-Farré, Montserrat Serra-Mas, Marta Otero-Viñas, and colleagues working across the University of Vic – Central University of Catalonia, the Institute for Research and Innovation in Life and Health Sciences in Central Catalonia, and the Institute for Research in Biomedicine in Barcelona. Their study stands out for its focus. Most proteomic investigations of PRP have examined samples from young or mixed-age donors, leaving a substantial evidence gap for the elderly, whose tissues are the ones most in need of regenerative support and whose blood may differ immunologically, hormonally, and in its clotting behavior.

The technical pipeline behind the study reflects the rigor required to make such claims defensible. Blood samples were collected from 32 elderly donors under institutional review board approval with informed written consent. Platelet-rich plasma was prepared by sequential centrifugation, the standard method of separating blood components by density. To release the platelet payload, the researchers activated the platelets with calcium gluconate and heparin, then centrifuged the samples again to strip out residual platelets, leaving behind the soluble protein cargo that a clinician would actually inject. Control plasma samples were processed in parallel to distinguish proteins genuinely concentrated by platelets from those simply circulating in blood.

Mass spectrometry formed the analytical core of the work. Because the most abundant blood proteins, chiefly albumin and immunoglobulins, can mask the rarer signaling molecules of interest, the team first depleted these high-abundance proteins. The remaining proteome was enzymatically digested into peptides and analyzed by liquid chromatography coupled to tandem mass spectrometry, a technique that separates peptides by chemical properties before fragmenting them in the mass spectrometer to infer their amino acid sequences. Bioinformatic pipelines then mapped the identified proteins onto known biological processes using tools such as Gene Ontology biological process annotations and the Kyoto Encyclopedia of Genes and Genomes pathway database.

The headline result is striking: 324 of the 1,378 detected proteins appeared exclusively in the platelet-rich plasma and not in control plasma. Functional analysis showed that the PRP proteome, whether unique to PRP or shared with plasma, was strongly linked to vesicle transport, immune and coagulation processes, cytoskeleton organization, and wound healing. In other words, the concentration step does not merely add platelet fragments; it enriches a coherent biological program centered on the very processes tissue repair demands. Cytoskeleton organization proteins point to cell migration and structural remodeling, while vesicle transport proteins reflect the exosome-rich cargo platelets deliver to injured tissue.

Perhaps the most clinically consequential finding, however, concerns variability. The researchers observed marked inter-individual differences in which proteins were detected across the 32 donor samples, and critically, the proteins showing this person-to-person variability were themselves linked to tissue regeneration processes. That observation carries a double meaning. On one hand, it suggests that not every elderly patient’s PRP preparation will be equally potent, a fact that could explain the notoriously inconsistent results of PRP clinical trials, where some patients respond robustly and others see little benefit. On the other hand, it opens a genuine opportunity for personalized medicine: rapid proteomic or functional screening of a patient’s PRP could, in principle, predict therapeutic quality before injection, or guide dosage and treatment protocols on an individual basis.

The study’s authors are careful about what their data do and do not establish. This is a characterization study, not a clinical trial; it demonstrates that elderly-derived PRP is rich in regenerative proteins and that its composition varies between people, but it does not yet prove that variations in the proteome translate into differences in healing outcomes for patients. Translating these molecular inventories into standardized, efficacy-graded PRP products will require correlating proteomic signatures with clinical endpoints in controlled studies, and the inter-individual variability the team documented is precisely the kind of biological signal that such trials should stratify for.

Still, the implications for an aging global population are considerable. As life expectancy rises, the burden of chronic wounds, osteoarthritis, tendinopathies, and other degenerative conditions grows with it, and the elderly are often the least well served by existing regenerative options. The new proteomic map provides reassurance that age does not strip PRP of its therapeutic cargo: even in advanced age, the platelet concentrate retains a wealth of proteins playing crucial roles in tissue regeneration. At the same time, it hands the field a molecular framework for moving beyond one-size-fits-all formulations toward personalized autologous therapies, where the composition of a patient’s own PRP becomes a measurable, and potentially optimizable, clinical variable. In a therapy long criticized for its biological opacity, that transparency may prove the most regenerative development of all.

The choice of activation agents in the study deserves particular attention, because it shapes what the mass spectrometer ultimately sees. Calcium gluconate mimics the physiological trigger for platelet activation, since rising intracellular calcium is the canonical signal that causes platelet granules to fuse with the cell surface and discharge their contents. Heparin, an anticoagulant, was used alongside it, and the combination allowed the researchers to drive degranulation in a controlled manner before removing the platelet bodies entirely. What remains after this step is the secretome: the soluble proteins, growth factors, and chemokines that would, in a living wound, be released directly at the site of injury. This design choice means the measured proteome approximates the bioactive payload a patient would actually receive, rather than an inventory of intact platelet contents.

The depletion of high-abundance proteins is equally consequential for interpreting the results. Albumin and immunoglobulins dominate blood plasma to such an extent that, undepleted, they can consume the vast majority of the mass spectrometer’s analytical capacity, drowning out low-copy signaling molecules. By removing them first, the team gained sensitivity into the mid- and low-abundance range where many regulatory proteins reside, including those governing extracellular matrix assembly and cell communication. This technical step helps explain why the study resolved nearly 1,400 distinct proteins, a depth of coverage that few earlier PRP characterizations achieved, and why proteins tied to vesicle transport and cytoskeletal dynamics emerged so prominently.

The finding that 324 proteins were detected only in platelet-rich plasma underscores how much the concentration step transforms the starting material. Platelets are not merely passive carriers; they are secretory cells whose alpha granules and dense granules hold a curated cargo accumulated during platelet production in the bone marrow. When activated, this cargo is released together with vesicles and microparticles that can deliver signaling molecules to target cells. The enrichment of vesicle transport proteins in the PRP samples is consistent with this biology, suggesting that the therapeutic effect of PRP may depend not only on soluble growth factors but also on the extracellular vesicles that platelets shed, which are increasingly recognized as mediators of intercellular communication in tissue repair.

The inter-individual variability documented across the 32 donors also invites reflection on its possible origins. Protein detection differences between donors could reflect genuine biological variation in platelet content, differences in circulating plasma proteins, or variation in how each donor’s blood responded to the preparation protocol. Age-related changes in platelet reactivity, chronic low-grade inflammation, comorbidities, and medication use are all plausible contributors in an elderly cohort, although the study design did not dissect these factors individually. What the data establish is that the variability itself concentrates in proteins associated with tissue regeneration, meaning the differences are not random noise scattered across irrelevant functions but are centered on the biology that matters therapeutically.

Methodologically, the work also contributes to reproducibility in a field often criticized for heterogeneity. The researchers reported quality control metrics including false discovery rate control for peptide and protein identification, and they deposited their data in the PRIDE proteomics repository, allowing other laboratories to reanalyze the raw spectra. Such transparency matters because PRP preparations differ widely across clinics in centrifugation protocols, activation methods, and platelet concentrations, making cross-study comparison difficult. A well-annotated molecular reference for elderly-derived PRP, produced under a documented preparation pipeline, gives the field a benchmark against which future formulations can be compared, and a foundation for the stratified clinical trials that will be needed to convert proteomic characterization into therapeutic guidance.

Subject of Research: Proteomic profiling of platelet-rich plasma from elderly individuals for autologous regenerative therapy

Article Title: Comprehensive proteomic profiling of platelet-rich plasma from elderly individuals: insights for autologous therapeutic applications

Article References: Buisan-Farré, A., Serra-Mas, M., Sarri, E., Salgado-Pacheco, V., Arauz-Garofalo, G., Odena-Caballol, A., Vilaseca, M., Gay, M., Ferrer-Solà, M., Masó-Albareda, C., Casals-Zorita, M., & Otero-Viñas, M. (2026). Comprehensive proteomic profiling of platelet-rich plasma from elderly individuals: insights for autologous therapeutic applications. Clinical Proteomics. https://doi.org/10.1186/s12014-026-09630-3

Image Credits: AI Generated

DOI: 10.1186/s12014-026-09630-3

Keywords: platelet-rich plasma, PRP, proteomics, mass spectrometry, elderly, tissue regeneration, regenerative medicine, autologous therapy, wound healing, coagulation, inter-individual variability, Clinical Proteomics