The Value of Combined Measuring of the Cerebrospinal Fluid Lactate and ‎Serum Procalcitonin in Diagnosis of Acute Bacterial Meningitis ‎

INTRODUCTION

Bacterial meningitis is an inflammation of the meninges due to bacterial infection and represents one of ‎the endemic diseases in Egypt [1,2]. Aseptic meningitis is an inflammation of meninges without evidence of ‎bacterial infection on bacterial cultures and Gram staining. It is usually accompanied by a mononuclear ‎pleocytosis [3].The commonest cause of bacterial meningitis is Neisseria meningitidis, Haemophilus ‎influenzae type b, Streptococcus pneumoniae [4], while the common cause of aseptic meningitis is viral ‎meningitis [5]. Acute bacterial meningitis requires early diagnosis and immediate intravenous administration of ‎antibiotics, whereas aseptic meningitis is usually self-limiting so, the delay of accurate treatment increases the ‎adverse outcomes. Furthermore, signs and symptoms are often non-specific in the early phases of meningitis, ‎and it is not always possible to make a  diagnosis based on the routine examination of CSF [6]. Positive CSF ‎bacterial culture and Gram staining are considered the gold standard in the diagnosis of bacterial meningitis. ‎However, they have poor sensitivity and the bacterial culture is time-consuming [7].‎

The serum and CSF markers currently used in bacterial meningitis diagnosis, as C-reactive protein, are also ‎characterized by poor sensitivity and specificity. Therefore, searching for reliable and valid markers with more ‎sensitivity and specificity for bacterial meningitis is required [8]. The level of CSF lactate was considered a ‎useful marker for the differentiation of bacterial meningitis from viral meningitis [9]. Procalcitonin (PCT) is a ‎‎116-amino-acid protein that is formed by the parafollicular cells of the thyroid, the neuroendocrine cells, and ‎the leukocytes. The level of serum PCT increases markedly in bacterial infections in response to various ‎proinflammatory cytokines. The raised level of PCT may be used as a good marker for the diagnosis of ‎bacterial meningitis [10,11]. This work aimed to assess the role of the combined measuring of CSF lactate and ‎serum procalcitonin in the diagnosis of acute bacterial meningitis‎.

PATIENTS AND METHODS

A cross-sectional study including 42 meningitis patients was conducted at Zagazig Fever Hospital and ‎Zagazig University Hospitals in the period from November 2018 to June 2019. Inclusion Criteria; Patients ‎with clinical picture suggestive of meningitis (headache, fever, projectile vomiting, nuchal rigidity, Kernig’s ‎sign, and Brudzinski’s signs) and CSF analysis suggestive of meningitis. Exclusion Criteria; Patients with ‎either of the following; a disease that causes an increase in CSF lactate such as epilepsy, intracranial ‎hemorrhage and malignancy, another site of infection besides meningitis, brain tumor, other causes of impaired ‎conscious levels or neurological insults, antibiotic treatment before admission and tuberculosis or fungal ‎meningitis.‎

Patients were divided according to their final diagnosis into two groups; group I included 13 patients ‎with bacterial meningitis (positive CSF bacterial culture and/or  Gram stain), group II included 29 patients ‎with aseptic meningitis (negative CSF  bacterial culture and Gram stain) [12,13]. All patients were exposed to:‎

• A thorough clinical assessment; including personal data, presenting complaints, general symptoms, ‎neurological symptoms, general examination, and neurological examination.‎
• Laboratory investigations; Complete blood count (CBC), Erythrocyte sedimentation rate (ESR), C ‎reactive protein (CRP), random blood sugar.‎
• Lumbar Puncture (LP) and CSF analysis; The patient assumed the lateral recumbent position. After ‎palpating the landmarks, preparing the skin was done with disinfectant and local anesthesia, the needle ‎was inserted in the inter-space between L3 and L4 or L4 and L5, in the midline and around 15 degrees ‎cephalic [14]. CSF analysis;1-Physical (aspect and pressure), 2- Cell count:  total and differential ‎leukocyte count, 3- Chemical glucose and protein content, 4- Bacteriological analysis culture, and ‎Gram stain. Patients with clinical risk factors for raised intracerebral pressure with subsequent risk for ‎cerebral herniation had a CT scan of the head before LP [15]. ‎
• CSF lactate level testing, by Cobas 6000 (c501, Roche, Japan), Test principle; colorimetric assay. ‎Normal level 1.1 – 2.4 mmol/L [16].‎
• Serum PCT level testing, by Cobas (e 601, Roche, Japan), Test principle; electrochemiluminescence ‎immunoassay. The normal level is < 0.05 ng/mL [11].‎
• Empiric treatment was initiated directly after CSF sampling or when it was deferred with the following ‎regimen: Vancomycin plus a third-generation cephalosporin (ceftriaxone or cefotaxime) plus ampicillin ‎‎(in adults > 50 years of age or children < 3 months) plus dexamethasone (starting before the first dose ‎of antibiotics) [8].‎

Statistical analysis

All information was gathered and arranged by utilizing SPSS 22.0 for windows (SPSS Inc., Chicago, ‎IL, USA) and Med Calc 13 for windows. Constant information is summarized as the mean ± SD and middle ‎‎(extend), and the qualitative data is presented as a number (frequency). Mann-Whitney U test was applied to ‎compare non-ordinarily dispersed data between the two groups. The Chi-square test or Fisher's precise test ‎were used to analyze qualitative data. Receiver operating characteristic (ROC) curve analysis was used to ‎identify optimal cut-off values. p < 0.05 was considered statistically significant.

RESULTS

This study included 42 meningitis cases (24 males and 18 females) with ages ranging from 6 months to 73 ‎years. There was no statistically significant difference between the two groups for gender and age (Table 1). ‎According to the results of CSF bacterial culture and Gram staining, the patients were divided into two groups; ‎the bacterial meningitis group (I) included thirteen patients (31%) who had a positive CSF bacterial culture and ‎Gram stain results., and the aseptic meningitis group (II) included twenty-nine patients (69%) who had a ‎negative CSF bacterial culture and Gram stain results. The isolated bacteria included Neisseria meningitidis in ‎‎7 cases, Streptococcus Pneumoniae in 3 cases, Haemophilus influenzae in 2 cases, Escherichia coli in one ‎case. Table 2, compared the clinical manifestations of the two groups and showed a significant increase in the ‎incidence of Kernig's sign, Brudzinski's sign, and neck stiffness (30.8%, 30.8%, 76.9% respectively) in the ‎bacterial meningitis group when compared with the aseptic meningitis group  (6.9%, 6.9%, 13.8% ‎respectively). The main presenting manifestation of bacterial meningitis in our study was fever  (100%), neck ‎stiffness (76.9%), headache (61.5%), disturbed level of consciousness (61.5%), convulsion (53.8), vomiting ‎‎(53.8%), Brudzinski (30.8%), and Kernig’s (30.8%).‎

Table 3 shows that the mean levels of blood total leukocyte count (TLC), ESR, and CRP in the bacterial ‎meningitis group (14.06 ± 6.85, 47.1 ± 26.9, 103.3 ± 99 respectively) were significantly more than the aseptic ‎meningitis group ( 9.574 ± 4.11, 14.0 ± 6.4, 13.8 ± 9.8 respectively). The CSF analysis of the studied cases ‎showed that the CSF TLC, polymorphonucleocyte (PMN), and protein levels ( 7500, 80 ± 9.1, 208.2 ± 83.1 ‎respectively ) were significantly higher in bacterial meningitis group than aseptic meningitis group (15, 18 ± ‎‎9.3, 53.6 ± 89.8 respectively ), whereas the CSF lymphocyte and glucose mean levels were significantly ‎higher in the aseptic meningitis group (81.9 ± 9.3, 73.6 ± 22 respectively) than the bacterial meningitis group ‎‎(19.5 ± 9.1, 42.0 ± 12.7 respectively). Serum PCT and CSF lactate levels were significantly higher in the ‎bacterial meningitis group (1.16 ±1.24, 7.5 ± 6.6, respectively) than patients with aseptic meningitis (0.059 ± ‎‎0.04, 3.98 ± 2.1, respectively). Table 4 illustrates that the combined measuring of serum PCT and CSF lactate ‎levels had a higher sensitivity, specificity, and accuracy (96.6%, 76.9%, 90.9% respectively) for the diagnosis ‎of bacterial meningitis than testing either of them alone.  ROC analysis showed a significant high area under ‎the curve (AUC) for the combined measuring of CSF lactate and serum PCT when compared with AUC for ‎measuring either of them only (figure 1).

 ‎DISCUSSION

Meningitis is a public health problem that requires an accurate and rapid diagnosis, which in turn ‎affects the disease management and outcome [6]. The already used tools as CSF Gram stain, cultures, and ‎chemical CSF examination, have limitations to diagnose and differentiate between bacterial and aseptic ‎meningitis. [18]. Therefore, this study aimed to evaluate the role of combined testing of serum PCT, and CSF ‎lactate in the diagnosis of bacterial meningitis.‎

Our study included 57.1% male and 42.9% female, with no significant difference for age and gender ‎distribution between bacterial and aseptic meningitis groups, these results agreed with those of Abro et al. [19], ‎Alkholi et al. [20]. The commonest presenting manifestation of bacterial meningitis was fever (100%), ‎followed by neck stiffness and headache, whereas Thomas et al.,  reported that headache (92%) followed by ‎fever (71%) were the main presenting symptoms for meningitis [21], this difference can be explained by ‎selection bias as our patients were recruited from a fever hospital.‎

The patients with bacterial meningitis in this study had significantly higher blood TLC, ESR, and CRP ‎levels than patients with aseptic meningitis. These results agreed with those of Makoo et al., who found a ‎significant difference between acute bacterial meningitis and aseptic meningitis regarding TLC and ESR and ‎CRP levels in favor of patients with bacterial meningitis [22]. This finding can be explained by the ‎hematological reaction in response to bacterial infection [23]. The patients with bacterial meningitis also had ‎significantly higher levels of CSF TLC, PMN, and protein than patients with aseptic meningitis, while they ‎had significantly lower levels of CSF glucose and lymphocyte than patients with aseptic meningitis. Many ‎studies reported similar findings [22,24]. The elevated CSF protein level is due to the disruption and increased ‎permeability of the blood-brain barrier by the bacteria and the immune system reaction[25]. The ‎hypoglycorrhachia (CSF glucose < 45 mg/dl) in bacterial meningitis is due to the disruption of glucose ‎diffusion and increased glucose consumption in response to bacterial infection [26].‎

CSF lactate level at a cut-off value ≥ 2.4 mmol/l showed a 66.7% diagnostic accuracy, 75.9% sensitivity, ‎‎46.2% specificity, 46.2% Negative predictive value (NPV), and 75.9% positive predictive value (PPV) which ‎seemed to be inadequate for differentiating bacterial meningitis from aseptic meningitis. This result nearly ‎agrees with Schwarz et al., who found that CSF lactate at cut-off value  ≥ 2.1 had a sensitivity of 94%, but the ‎specificity was low (42%) and considered it a weak and unsatisfactory marker for differentiating bacterial and ‎aseptic meningitis [27], on the other side, many studies reported high sensitivity, specificity, and NPV but at a ‎higher cut off values (3 - 3.5 mmmol/l) and concluded that CSF lactate could help in the diagnosis of bacterial ‎meningitis [28,29,30], this controversy makes the combination of biomarkers more favorable than single ‎biomarker as recommended recently by Danish study, which found that combination of biomarkers increased ‎the predictive value and recommended against using a single biomarker alone to establish or exclude the ‎diagnosis [29].  ‎

Our study showed that serum PCT level at a  cut-off value  ≥ 0.075 ng/dl was a reliable biomarker in ‎differentiating bacterial meningitis from aseptic meningitis (the diagnostic accuracy 85.7%, sensitivity 93.1% ‎specificity 69.2%, NPV of  81.0%, and PPV of 87.1%).  Different studies showed wide variations in the ‎sensitivity, specificity, and cut-off values of serum PCT, this variation could be attributed to the diverse age ‎range and nature of the study populations [20]. We statistically analyzed the combined testing of both the ‎serum PCT and CSF lactate, to determine their diagnostic usefulness as a novel and clinically feasible ‎diagnostic indicator of bacterial meningitis. The combined measuring of serum PCT and CSF lactate data ‎demonstrated increased sensitivity (96.6%), specificity (76.9%), PPV (90.3%), NPV (90.3%), and accuracy ‎‎(90.9%), when compared with the measuring of either of them only. Although serum PCT showed relatively ‎high accuracy (85.7%), the combined testing of serum PCT and CSF lactate demonstrated more accuracy ‎‎(90.9%) than serum PCT alone. this result indicates that combined measuring of both tests could be a useful ‎diagnostic parameter for accurate differentiation of acute bacterial from aseptic meningitis.‎

Limitations ‎

Small study population. Unavailability of Polymerase chain reaction test in Zagazig fever hospital. It can help ‎in identifying the pathogen, particularly if negative CSF culture and could be a standard reference test for the ‎validation of serum PCT and CSF lactate.  ‎

CONCLUSION

‎The combined measuring of both serum procalcitonin and CSF lactate levels is highly accurate in the diagnosis ‎of bacterial meningitis cases and helps to differentiate bacterial meningitis from aseptic meningitis. ‎

Recommendations: Measuring both CSF lactate and serum PCT in routine workup of suspected meningitis ‎cases to help in the diagnosis of bacterial meningitis while awaiting the culture results. Multi-center studies ‎with a large sample size to compare the combined testing of  CSF lactate level and serum PCT with other ‎noninvasive markers, and to assess its prognostic value. ‎

Ethical considerations: A review board of the Tropical Medicine Department of Zagazig University ‎approved the protocol in concordance with the Medical Association Code of Ethics (declaration of Helsinki). ‎Written informed consent was taken from all participants.‎

Funding: None. ‎

Conflicts of interest: No conflict of interest.‎