Tests
1st tests to order
CT head
Test
This is the standard diagnostic test for SAH and should be ordered if SAH is suspected.[52]
Modern, third-generation scanners have dramatically improved the sensitivity of detecting subarachnoid blood, reaching 100% when performed within 6 hours of headache onset and read by experienced neuroradiologists.[55][56][57] In patients who present <6 hours from symptom onset of acute onset severe headache, a noncontrast head CT performed on a high-quality scanner and interpreted by a board-certified neuroradiologist is reasonable to diagnose/exclude aneurysmal SAH.[37] In patients with acute onset of severe headache who present >6 hours from symptom onset or who have a new neurologic deficit, a negative noncontrast head CT should prompt a lumbar puncture to diagnose/exclude aneurysmal SAH.[37] CT may also show subdural or parenchymal hematoma, hypodensities, hydrocephalus, and sometimes the aneurysm(s) if large or thrombosed.[54]
Result
hyperdense areas in the basal cisterns, major fissures, and sulci
CBC
Test
This is a nonspecific test. Leukocytosis following SAH is an independent risk factor for cerebral vasospasm.[89]
Result
may show leukocytosis
clotting profile
Test
Coagulopathy may be present.
Result
may show coagulopathy: elevated INR, prolonged PTT
serum electrolytes
Test
Hyponatremia is usually associated with syndrome of inappropriate antidiuretic hormone secretion (SIADH).[7] It may also occur due to salt wasting.[7][48] Hyponatremia occurs in up to 50% of patients.[90] It is associated with increased morbidity including vasospasm.[91]
Result
may show electrolyte abnormalities
troponin I
Test
Elevated in 20% to 28% of cases during the first 24 hours, in the absence of coronary artery disease.[44][50] This elevation in troponin I is an order of magnitude less than what is usually seen in the setting of myocardial infarction, and it seems to be associated with an increased risk of delayed cerebral ischemia, poor outcome, and death following SAH.[51][92]
Result
may be elevated
serum glucose
Test
Hyperglycemia develops in one third of SAH patients and is a feature of any acute brain injury. It is associated with poor clinical condition on admission and independently associated with poor outcome.[39]
Result
may be elevated
Tests to consider
lumbar puncture (LP)
Test
In patients with acute onset of severe headache who present >6 hours from symptom onset or who have a new neurologic deficit, a negative noncontrast head CT should prompt a lumbar puncture to diagnose/exclude aneurysmal SAH.
Cerebrospinal fluid (CSF) opening pressure should be measured. Four tubes of CSF should be collected and examined for gross blood. A serial count of red blood cells in tubes 1 to 4 is not sufficiently accurate to distinguish SAH from a traumatic LP. Visual inspection for xanthochromia is unreliable. Spectrophotometric analysis of hemoglobin degradation products is most reliable.[59]
Xanthochromia is an indicator of the presence of blood in the subarachnoid space.
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Result
bloody CSF (xanthochromia)
digital subtraction angiography (DSA)
Test
DSA is considered the gold-standard modality for the evaluation of cerebrovascular anatomy and aneurysm geometry and can aid in decision-making on the choice of optimal treatment modality.[37] AHA/ASA recommends that in patients with spontaneous SAH with high level of concern for aneurysmal source and a negative or inconclusive CT angiography (CTA), digital subtraction angiography (DSA) should be performed to diagnose/exclude cerebral aneurysm(s).[37] For diffuse SAH, DSA is indicated for evaluation regardless of CTA results because small aneurysms or other vascular lesions may not be fully appreciated or defined on CTA imaging owing to limitations in spatial resolution.[74][76][77][78][79]
Result
aneurysm
computed tomography angiography (CTA)
Test
CTA is widely available and often is the next diagnostic test performed when SAH is diagnosed with noncontrast CT.[37] A meta-analysis reported CTA to have a sensitivity of 92.7% and specificity of 77.2%, though another reported sensitivity and specificity surpassing 95%, especially when newer-generation multidetector scanners were used.[68][69][72][73]
CTA head sensitivity for detecting aneurysm decreases for aneurysms <3 mm in size in the setting of diffuse SAH, and for aneurysms occurring adjacent to an osseous structure.[67] CTA head may be sufficient to rule out a vascular cause of SAH when the location of hemorrhage is isolated to the perimesencephalic region with follow-up catheter-directed angiography indicated in CTA negative diffuse or peripheral SAHs.[67][74] However, there remains equipoise concerning the appropriate diagnostic pathway for a perimesencephalic distribution of SAH with CTA alone versus catheter-based DSA.[37]
Result
aneurysm
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