Lumbar puncture (LP) is still an important modality in the diagnosis of subarachnoid hemorrhage (SAH). Rapid and correct fluid analysis can provide patients with a better prognosis by appropriate intervention.
To determine the value of cerebrospinal fluid lactate dehydrogenase level in differentiation between SAH and traumatic LP.
This was a cross-sectional observational study. Patients with a diagnostic suspicion of SAH who were admitted to the emergency department were enrolled in our study based on the inclusion criteria. All patients underwent head computed tomography scan without contrast. Patients with SAH confirmed on computed tomography scan and those who needed surgical intervention underwent LP by the neurosurgical service in the operation room (group 1). Other patients who fulfilled the inclusion criteria but had a traumatic LP in the emergency setting were also enrolled in our study (group 2). The fluid samples of all LPs were sent to the laboratory to be analyzed. Finally, we compared the results of the 2 groups with each other.
Fifty-two patients were enrolled in our study, 26 patients (50%) from each group. The cerebrospinal fluid lactate dehydrogenase level was significantly higher in group 1 than it was in group 2 (P < .001), and based on receiver operating characteristic curve analysis, the significant level of cerebrospinal fluid lactate dehydrogenase to differentiate SAH from traumatic LP was estimated to be 185. The red blood cell and white blood cell counts were significantly higher in group 1 than they were in group 2 (P < .001).
Cerebrospinal fluid lactate dehydrogenase can effectively differentiate SAH from traumatic tap in LP samples.
Subarachnoid hemorrhage (SAH) is the pathologic state of accumulating blood in the subarachnoid space, and it can be life threatening. In addition, SAH is the leading cause of stroke in 5% of cases.1 Generally speaking, head trauma is the most common cause of SAH. The most common cause known as the main etiology of spontaneous SAH is intracranial aneurysm. Its prevalence is 9 persons per 100 000 annually. It is more common in older age and women.1 The SAH mortality has decreased significantly in recent years because of early diagnosis.
The diagnostic hallmark of SAH is sudden and severe headache with a positive predictive value of nearly 93%. Eighty percent of patients report it as the worst headache experienced in their lifetime.2
Brain computed tomography (CT) scan without contrast is the first imaging in SAH management. Its value in diagnosing SAH depends on the amount of hemorrhage, time of bleeding, and machine quality.1 Lumbar puncture (LP) should be considered when the results of CT scan are within reference range and there are no contraindications. Sometimes, analyzing cerebrospinal fluid (CSF) seems challenging. Red blood cells (RBCs) are important indicators of bleeding in subarachnoid space, but that interpretation has both false-positive and false-negative results.3 Traumatic tap can cause false-positive results in LP samples. Many indicators have been introduced to help physicians in differentiating SAH from traumatic tap, such as:
A decrease in RBC count in serial tube specimens from tube 1 to tube 4 can provide a clue. Although this method is not reliable, it can provide a clue to traumatic LP.3 The likelihood ratio of this test for SAH, depending on the percentage of change in RBC count between the final and initial tubes, has a 95% CI of 3.6 (range, 2.7–4.7) for less than 63% change in RBC count and a 95% CI of 0.1 (range, 0.03–0.4) for more than 63% change in RBC count.4
Xanthochromia is a yellowish color change in the centrifuged CSF, which results from RBC hemolysis and is suggestive of, but not pathognomonic for, SAH.5 Sensitivity (95% CI), specificity (95% CI), and the likelihood ratio for this test are 50% (range, 1%–99%), 97% (range, 93%–99%), and 15.57% (range, 3.25%–74.54%), respectively, for visual detection, and 100% (range, 16%–100%), 29% (range, 23%–35%), and 1.17% (range, 0.70%–1.96%), respectively, for spectrophotometric detection.6
An RBC count greater than 10 000 favors a diagnosis of SAH. The likelihood ratios (95% CI) for this test for SAH, depending on the RBC count, are 0% (range, 0%–0.3%) for RBCs less than 100, 1.6% (range, 1.1%–2.3%) for RBC greater than 100 but less than 10 000, and 6.3% (range, 3.0%–13.1%) for RBCs greater than 10 000.4
Moreover, RBCs in the CSF can produce lactate dehydrogenase (LDH) after being lysed by time. That process requires at least 2 hours to become measurable in the CSF; thus, its level in traumatic tap should be less than that of SAH. The hypothesis is that because RBCs have a high concentration of LDH, the LDH is likely to be elevated in SAH compared with a traumatic tap. In this study, we compared CSF LDH levels in SAH and in traumatic LPs.
MATERIALS AND METHODS
Participants
This study was approved by the ethics committee of Tehran University of Medical Sciences (Tehran, Iran) with an ethics code of 118359. All patients were required to read an informed consent letter, which they signed if they accepted participation in our observational and cross-sectional study. The study was performed in tertiary referral centers of Tehran (Shariati and Sina hospitals) from April 2015 to April 2016.
Our inclusion criteria were diagnostic suspicion of SAH with symptoms' onset of longer than 2 hours or persistent indications for LP in the emergency department. Patients were excluded if they were unwilling to participate in the study, if their diagnosis of SAH was confirmed in a CT scan but they didn't have the indications for surgical operation, their clinical manifestations of SAH were persistent for longer than 2 weeks, and their elevated CSF LDH level had another cause, such as infectious diseases (meningoencephalitis), malignancies, inflammatory diseases (multiple sclerosis, systemic lupus erythematosus cerebritis), or cerebrovascular thrombosis.
All patients with a diagnostic suspicion of SAH who were admitted to the emergency departments of Shariati and Sina hospitals (Tehran, Iran) and fit within the inclusion criteria were enrolled in our study. All patients underwent brain CT scan. In cases with SAH confirmation on CT scan and surgical indications, LP was performed in the operating room by the neurosurgical team. Those patients constituted group 1.
Other patients who had any indication for an LP in the emergency department (except those who met the exclusion criteria) and their sample was a traumatic tap compromised group 2. We considered an LP as traumatic if the operator could see blood inside the LP needle. Both groups' samples were analyzed in the laboratory for cell count, biochemistry, LDH level, and smear and culture. Concomitant complete blood cell counts, serum glucose, and LDH levels were drawn and sent to the laboratory.
Primary and Secondary Endpoints
Our primary outcome was LDH levels in the CSF of patients with SAH, compared with patients who had a traumatic tap. By this evaluation, we might be able to determine the significant cutoff point in LDH levels in the CSF to differentiate SAH from traumatic tap. Our secondary outcomes were comparing RBC and white blood cell (WBC) counts, glucose and protein levels in the CSF, and all other demographic data between the 2 groups.
Statistical Analysis and Sample Size Calculation
If the CSF level of LDH in a traumatic tap less than 2 hours was 120, and we expected it to increase at least 20% in SAH, the sample size needed could be calculated as 26 patients in each group (SD, 25; α = 0.05; power, 80%).
The data are presented as means and median values or proportions, and differences in those values are presented with accompanying 95% CIs. Variables were tested for normality (Kolmogorov-Smirnov test) before analysis. Analytic statistical tests included the unpaired, 2-tailed t test for continuous, normally distributed data and the Mann-Whitney U test for nonnormal and ordinal data. The χ2 and Fisher exact tests were used to compare proportions of the qualitative variables. The level of significance was .05. To determine the significant cutoff point in CSF LDH level to diagnose SAH, we used receiver operating characteristic curve. The SPSS for Windows software (IBM Corporation, Armonk, New York) was used for all data analysis.
RESULTS
Fifty-two patients were enrolled in our study, 26 cases (50%) in each group. All 26 patients (100%) in group 1 underwent LP by the neurosurgery team in the operating room, and all (100%) had SAH in their brain CT scans. The mean (SD) age of patients in groups 1 and 2 were 45.96 (17.09) and 52.87 (18.20), respectively. The patients in these groups had no significant differences in age (P = .56). In group 1, 20 patients (77%) were men and 6 (23%) were women. In the group 2, 13 patients (50%) were men, and 13 (50%) were women. Gender distribution had no significant difference between the 2 groups (P = .08).
Those data showed that the CSF LDH level in SAH was significantly higher than it was in traumatic LP. The median CSF LDH level in the SAH group was 477 U/L greater than traumatic tap group (P < .001). None of the patients (0%) with traumatic tap had CSF LDH levels greater than 210 U/L.
We used receiver operating characteristic curve (Figure) to define the cutoff point for CSF LDH to differentiate SAH from traumatic LP. Based on the area under curve, we found that the CSF LDH level could be predictive in differentiating these 2 situations. The best LDH level in CSF for differentiating SAH from traumatic tap was 185 U/L. According to that significant cutoff point, 21 patients (81%) in group 1 and only one patient (4%) in group 2 had CSF LDH above 185 U/L. Validity of that level is shown in Table 3.
Receiver operating characteristic (ROC) curves of cerebrospinal fluid (CSF) lactate dehydrogenase (LDH) and CSF red blood cells (RBCs).
Receiver operating characteristic (ROC) curves of cerebrospinal fluid (CSF) lactate dehydrogenase (LDH) and CSF red blood cells (RBCs).
DISCUSSION
Differentiation between SAH and traumatic LP is an important, yet difficult, task in some situations. There is limited evidence to guide physicians under those conditions, and most studies in this field were performed on animals. Different studies have used CSF RBC and WBC counts and protein levels to determine SAH in lots of LP samples, but they are incapable of definitely determining significant cutoff points for those values. Shah et al3 reported in 2002 that, despite the effective and valuable role of brain CT scans in the diagnosis of SAH, they might not show bleeding during its early hours. Shah and colleagues3 also emphasized using xanthochromia by spectrophotometry rather than visual techniques. Nagy et al,7 in a review of cases from 1990 to 2013, concluded that differentiating SAH from traumatic tap was important, yet difficult, for emergency department physicians. They found that visual analysis of xanthochromia was not reliable, and its usage should be discontinued.
The UK National External Quality Assessment Scheme for Immunochemistry Working Group,8 in 2003, evaluated CSF bilirubin levels in SAH and concluded that the high levels of bilirubin in CSF could suggest a diagnosis of SAH. Perry et al9 enrolled 1739 awake patients older than 15 years who had severe headaches. They concluded that a sensitive cutoff point for RBC counts in SAH was more than 2000 ×106/L.
In our study, determination of the RBC count in SAH was a secondary outcome. We found that variable was significantly increased in group 1 compared with group 2. Our study revealed that the CSF LDH levels in patients with SAH were also significantly increased in patients with a traumatic tap. The hypothesis is that because RBCs have a high concentration of LDH, it is likely more elevated in SAH than it is with a traumatic tap. Receiver operating characteristic curve defined that cutoff point as 185 U/L, which means that if the CSF LDH level of a patient who is suspicious for SAH is more than 185 U/L, the diagnosis can be confirmed with 81% sensitivity (21 of 26 patients). None of our samples with CSF LDH levels greater than 210 U/L had a traumatic tap.
Shuttleworth et al10 studied 22 rabbits with induced SAH in 1977 and measured the CSF LDH level of their LP samples during the first 24 hours. They concluded that CSF LDH levels in SAH were significantly higher than those with traumatic tap. They recommended its usage in human studies. In 2016, Wu et al11 reported that elevation of CSF interleukin-6 and tumor necrosis factor α levels could be 2 important biomarkers for early diagnosis and disease follow-up in SAH. Kellermann et al,12 in 2016, confirmed that serum and CSF S100B levels were significantly higher in traumatic brain injury than they were in SAH, and that higher level was associated with a worse patient outcome.
Limitations of the Study
One of the limitations of our study was the few patients with SAH in the emergency department; thus, we had to collect LP samples in the operating room from the neurosurgical team. Our sample size was not large enough to expand the results to a bigger population. Additional human studies are needed for a definitive differentiation of SAH from traumatic tap using an accurate cutoff point in CSF LDH levels.
CONCLUSIONS
Cerebrospinal fluid LDH levels might be helpful in differentiating between SAH and traumatic tap.
We thank the patients who have participated in this study.