Gastroenterology
Volume 135, Issue 3 , Pages 731-733, September 2008

Ascites Fluid Lactoferrin: Data Emerges for a Logical Biomarker

  • Eric R. Kallwitz

      Affiliations

    • Corresponding Author InformationAddress requests for reprints to Eric R. Kallwitz, MD, 840 S Wood Street MC 787, 10th Floor CSB, Chicago, Il 60612. fax 312-996-1334

Section of Hepatology, Department of Internal Medicine, University of Illinois at Chicago, Chicago, Illinois

published online 08 August 2008.

Article Outline

 

See “Ascitic Fluid Lactoferrin for Diagnosis of Spontaneous Bacterial Peritonitis,” by Parsi MA, Saadeh SN, Zein NN, et al, on page 803.

Spontaneous bacterial peritonitis (SBP) is an important cause of morbidity and mortality in patients with cirrhosis and ascites. SBP is identified in 10%–30% of patients hospitalized with ascites,1 and mortality can approach 30%.2 The diagnosis of SBP requires a high index of suspicion, because many affected patients do not have symptoms such as abdominal pain, fever, or encephalopathy at the time of presentation. Therefore, it is recommended that all patients with cirrhosis and ascites undergo a paracentesis at the time of hospital admission to assess for SBP.1, 3 Paracentesis is commonly performed in emergency departments as well as in the outpatient setting to evaluate new-onset ascites and to manage diuretic-resistant or refractory ascites.3 Although SBP is not as prevalent in the outpatient setting, it is reasonable to evaluate ascitic fluid for SBP in these patients as well.

The diagnosis of SBP is based on a polymorphonuclear leukocyte (PMN) count ≥250/mm3.1, 3 The cell count and differential are generally performed manually, although automated cell counts may give comparable results.4 An elevated PMN count alone is sufficient to establish the diagnosis of SBP as ascitic and blood cultures are often negative.1, 3 The rapid diagnosis of SBP and institution of antibiotic therapy are critical owing to the high mortality associated with this condition. However, the diagnosis may be delayed when hospital laboratory personnel are not available at off hours and in the office setting where specimens are sent to an offsite laboratory. In some settings, clinicians do not receive the results of an ascites cell count until the following day.

As a result of the potential for delays in the diagnosis of SBP, there has been interest in developing a surrogate test to identify an elevated ascites PMN count. Ideally, such a test should be performed at the bedside at the time of paracentesis and should have a high sensitivity and a low false-positive rate. Leukocyte reagent strips, used to analyze urine samples, were evaluated in an initial attempt to develop a rapid screening test for the diagnosis of SBP.5, 6, 7 Data from small pilot studies seemed promising, with a sensitivity that ranged between 83% and 100%.5, 6, 7 However, in a large clinical trial of 1041 patients undergoing 2,123 procedures, leukocyte reagent strips with a threshold of 2+ for positivity had a sensitivity of only 45% (Table 1).8 Even when lowering the threshold for positivity to trace positive the sensitivity of the test only improved to 79%.9 Although specificity remained high in most studies and a strong positive result could predict SBP, the varied sensitivity in clinical trials make current leukocyte reagent strips suboptimal for the diagnosis of SBP.

Table 1. Comparison With Prior Studies of Reagent Strips for the Diagnosis of SBP
StudyMethodNumber PatientsNumber SamplesSensitivitySpecificityPPVNPV
Butani et al5Multistix 10SG ≥27513683999198
Castellote et al6Reagent strip ≥212822896897499
Vanbiervliet et al7Multistix 8SG >“trace”7272100100100100
Nousbaum et al8Multistix 8SG ≥2+1041212345997897
Parsi et al10⁎Lactoferrin ≥242 ng/mL14821896977899

⁎PPV and NPV were calculated based on the author's sensitivity, specificity, and number of patients.

This issue of Gastroenterology includes an important study by Parsi et al10 that evaluated a novel use of lactoferrin as a biomarker for SBP. Lactoferrin is an iron-binding protein contained in PMNs that is released on degranulation.11, 12 Titers of lactoferrin correlate with absolute neutrophil count in blood samples, and with the presence of neutrocytic inflammation in body fluids such as sputum samples.13 In the gastrointestinal tract, previous studies showed that lactoferrin provides a reliable marker of inflammatory diarrhea. Similar to the proposed utility of lactoferrin in the diagnosis of SBP, measurement of fecal lactoferrin was evaluated as a means to diagnose inflammatory diarrhea in a community setting where cell lysis and specimen transport might result in false-negative results.14, 15 These early pilot studies evaluated quantitative measures of lactoferrin, but qualitative assays also exist. A subsequent study showed that a commercial latex agglutination kit had a sensitivity of 90% and specificity of 98% to distinguish patients with inflammatory bowel disease from those with other causes of diarrhea and from healthy controls.16

The study by Parsi et al10 represents a promising approach to developing a rapid and reliable assay for the diagnosis of SBP. The authors proposed that lactoferrin would act as a surrogate marker for PMNs in ascites fluid for the reasons delineated above. Lactoferrin levels were measured in ascites fluid from 218 samples obtained from 148 patients. Ten percent of samples had evidence of SBP based on cell count. ROC analysis identified an optimal lactoferrin level of 242 ng/mL to distinguish the presence of SBP. Ascites lactoferrin concentrations ≧242 ng/mL had a sensitivity of 96% and specificity of 98% to identify a PMN count >250/mm3. This was based on 21 of 22 patients who presented with SBP and had a lactoferrin level ≥242 ng/dL. Additionally, lactoferrin levels decreased to <242 ng/dL in 17 of 18 patients who had a decline in PMN count to <250/mm3 after treatment with antibiotics. In both the diagnostic and the posttreatment setting, lactoferrin levels correlated closely with ascitic fluid PMN count. The authors proposed that commercially available kits might be developed and used to establish a qualitative bedside assay.

The strength of the current study is the logical hypothesis that the measurement of ascitic fluid lactoferrin could provide a reliable biomarker for the presence of PMNs, which was validated by the results thus far. Further issues regarding the use of lactoferrin in the diagnosis of SBP deserve comment. A small number of samples with SBP were included in this initial study, comparable with the early studies of leukocyte reagent strips shown in Table 1. Studies including larger numbers of patients with SBP should be performed to validate the results and to further assess the optimal lactoferrin threshold to identify an elevated ascites PMN count. Lactoferrin levels also need to be defined in traumatic taps and in hemorrhagic ascites, which could potentially predispose to false-positive results. Correction factors for the PMN count in hemorrhagic ascites have been defined.1

A further consideration is whether lactoferrin testing for SBP should be applied to all patients undergoing paracentesis. In series of outpatients undergoing paracentesis, SBP was identified in only 0%–3.5% of samples.8, 17, 18 In this setting, with a low pretest probability for SBP, the positive predictive value of the test is reduced. The utility of measuring ascitic fluid lactoferrin in outpatients where a low prevalence of SBP is observed needs to be evaluated. After passing these hurdles, the next step would be the development and testing of a qualitative bedside assay to identify ascites lactoferrin levels associated with SBP. Although the initial results are promising, much work is needed before lactoferrin testing can enter the realm of clinical practice.

In an era where organ availability is limited, the care of patients with complications of cirrhosis requires meticulous attention to detail and rigorous follow-up. For clinicians with busy practices and for house staff or hospitalists taking care of large numbers of patients with liver disease, a rapid test to identify patients with SBP would be quite useful. Lactoferrin, a product of activated PMNs, is a logical marker. Perhaps in time, a qualitative assay for lactoferrin will make it possible to diagnosis SBP at the bedside. Until then, the ascites cell count remains the standard diagnostic test.

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References 

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PII: S0016-5085(08)01423-6

doi:10.1053/j.gastro.2008.07.037

Refers to article:

  • Editorial Accompanies Article Ascitic Fluid Lactoferrin for Diagnosis of Spontaneous Bacterial Peritonitis , 22 May 2008

    Mansour A. Parsi, Sherif N. Saadeh, Nizar N. Zein, Gary L. Davis, Rocio Lopez, James Boone, Maria R. Lepe, Linsheng Guo, Mohammad Ashfaq, Goran Klintmalm, Arthur J. McCullough
    Gastroenterology September 2008 (Vol. 135, Issue 3, Pages 803-807)

Gastroenterology
Volume 135, Issue 3 , Pages 731-733, September 2008

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