Fisher Grade Calculator
Grade subarachnoid hemorrhage on CT using the Fisher classification for vasospasm risk. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateStandard monitoring with serial neurological exams. Nimodipine prophylaxis recommended. Repeat CT if clinical change. Low probability of symptomatic vasospasm but continued vigilance warranted.
Formula
Original Fisher: Grade 1 = no blood, Grade 2 = diffuse thin (<1mm) blood, Grade 3 = thick (>1mm) clot, Grade 4 = ICH/IVH with diffuse or no SAH. Modified Fisher incorporates IVH presence with SAH thickness for improved vasospasm prediction.
Last reviewed: January 2026
Worked Examples
Example 1: Fisher Grade 3 with High Vasospasm Risk
Example 2: Modified Fisher Grade 4
Background & Theory
The Fisher Grade Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Fisher Grade Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Key Features
- Calculates both weighted and unweighted GPA from course grades and credit hours, supporting common 4.0 and 5.0 scale systems used by US high schools and universities.
- Converts raw percentage scores to letter grades using customizable grading scales, and maps letter grades back to GPA points for transcript analysis.
- Assesses text reading difficulty using Flesch-Kincaid Grade Level and Gunning Fog Index formulas, returning a target grade level and readability score.
- Generates a recommended weekly study schedule based on enrolled credit hours and subject difficulty weighting, helping students allocate preparation time effectively.
- Determines the minimum score needed on a final exam or assignment to reach a target overall course grade, given current scores and their respective weights.
- Estimates scholarship and need-based financial aid eligibility by combining GPA thresholds, enrollment status, and household income inputs against standard award criteria.
- Converts between credit hours, contact hours, and Carnegie units across semester and quarter systems, useful for transfer credit evaluation and course equivalency mapping.
- Looks up standardized test score percentile rankings for exams including the SAT, ACT, GRE, and GMAT, showing how a given score compares to the test-taking population.
Frequently Asked Questions
Sources & References
- 1Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by CT scanning. Neurosurgery. 1980;6(1):1-9
- 2Claassen J et al. Effect of cisternal and ventricular blood on risk of delayed cerebral ischemia after SAH. Stroke. 2001;32(9):2012-2020
- 3Frontera JA et al. Prediction of symptomatic vasospasm after SAH: the modified Fisher Scale. Neurosurgery. 2006;59(1):21-27
Formula
Fisher Grade 1-4 based on CT appearance of subarachnoid blood
Original Fisher: Grade 1 = no blood, Grade 2 = diffuse thin (<1mm) blood, Grade 3 = thick (>1mm) clot, Grade 4 = ICH/IVH with diffuse or no SAH. Modified Fisher incorporates IVH presence with SAH thickness for improved vasospasm prediction.
Worked Examples
Example 1: Fisher Grade 3 with High Vasospasm Risk
Problem: A 48-year-old woman presents with thunderclap headache. CT head shows thick subarachnoid blood greater than 1 mm in the basal cisterns and left Sylvian fissure with no intraventricular hemorrhage.
Solution: CT findings: Localized thick subarachnoid blood (>1 mm layer)\nNo intraventricular hemorrhage\nOriginal Fisher Grade: 3 (thick clot/blood >1 mm)\nModified Fisher Grade: 3 (thick SAH, no IVH)\nVasospasm risk (original): 30-70%\nVasospasm risk (modified): 30-40%
Result: Fisher Grade 3 - High vasospasm risk requiring aggressive TCD monitoring and nimodipine prophylaxis
Example 2: Modified Fisher Grade 4
Problem: A 62-year-old man with sudden loss of consciousness. CT shows thick subarachnoid hemorrhage in bilateral Sylvian fissures and basal cisterns with blood in the third and fourth ventricles.
Solution: CT findings: Thick subarachnoid blood (>1 mm) in multiple cisterns\nIntraventricular hemorrhage present in third and fourth ventricles\nOriginal Fisher Grade: 4 (intraventricular clot with diffuse SAH)\nModified Fisher Grade: 4 (thick SAH with IVH)\nVasospasm risk (modified): 40-50%\nConsider EVD placement for hydrocephalus
Result: Modified Fisher Grade 4 - Very high vasospasm risk with IVH; consider EVD and aggressive monitoring
Frequently Asked Questions
What is the Fisher Grade and what does it measure?
The Fisher Grade is a radiological classification system developed by Dr. C. Miller Fisher in 1980 to categorize the amount and distribution of subarachnoid hemorrhage (SAH) visible on computed tomography (CT) scans. The primary purpose of this grading system is to predict the risk of cerebral vasospasm, a dangerous narrowing of brain blood vessels that typically occurs 4-14 days after the initial hemorrhage. The scale ranges from Grade 1 (no visible blood) to Grade 4 (intracerebral or intraventricular clot), with Grade 3 (thick subarachnoid blood) carrying the highest vasospasm risk. It is routinely assessed on the initial CT scan in emergency departments.
What is the difference between the original and modified Fisher Scale?
The original Fisher Scale, published in 1980, has four grades based on the amount of subarachnoid blood on CT. However, it has a paradoxical relationship where Grade 4 has lower vasospasm risk than Grade 3. The modified Fisher Scale, proposed by Claassen and colleagues in 2001, addresses this limitation by incorporating both the thickness of subarachnoid blood (thin vs thick) and the presence or absence of intraventricular hemorrhage (IVH). The modified version provides a more linear correlation between grade and vasospasm risk, making it more clinically useful. Many contemporary neurocritical care units now prefer the modified Fisher Scale because of its improved predictive accuracy for delayed cerebral ischemia.
How is the CT scan evaluated for Fisher grading?
Fisher grading requires careful evaluation of the initial non-contrast CT scan of the head performed after suspected subarachnoid hemorrhage. The radiologist or clinician assesses several features: the presence or absence of subarachnoid blood in the basal cisterns, Sylvian fissures, and interhemispheric fissure; the thickness of the blood layer (less than 1 mm vs 1 mm or greater for the original scale); the presence of localized blood clots; and the presence of intraventricular hemorrhage (IVH) or intracerebral hemorrhage (ICH). The CT should ideally be performed within 24 hours of symptom onset for optimal sensitivity. Modern high-resolution CT scanners have improved detection of subtle subarachnoid blood compared to older technology.
What is the role of nimodipine in Fisher Grade management?
Nimodipine is a calcium channel blocker that is the only pharmacological agent with strong evidence for improving outcomes after subarachnoid hemorrhage. It is recommended for all SAH patients regardless of Fisher Grade, typically administered as 60 mg orally every 4 hours for 21 days. While nimodipine has not been definitively shown to prevent angiographic vasospasm, it does reduce the incidence of delayed cerebral ischemia and improve neurological outcomes. The drug works through neuroprotective mechanisms beyond simple vasodilation. Patients with higher Fisher Grades (particularly Grade 3) who are at greatest vasospasm risk may benefit most from strict adherence to the nimodipine protocol, along with hemodynamic optimization and close monitoring.
What is delayed cerebral ischemia and how does Fisher Grade predict it?
Delayed cerebral ischemia (DCI) is a clinical syndrome occurring after subarachnoid hemorrhage, characterized by new neurological deficits or infarction on imaging that cannot be attributed to other causes such as rebleeding, hydrocephalus, or metabolic derangements. DCI typically occurs between days 4 and 14 after the hemorrhage and affects approximately 30% of SAH patients. The Fisher Grade, particularly the modified version, is one of the strongest predictors of DCI. Higher grades with thicker subarachnoid blood and intraventricular hemorrhage correlate with increased DCI risk. This relationship exists because larger volumes of blood in the subarachnoid space lead to greater release of blood breakdown products that trigger arterial vasospasm and inflammation.
When should the Fisher Grade be reassessed after initial CT?
The Fisher Grade is typically assigned based on the initial CT scan obtained at presentation, as this provides the most relevant prognostic information for vasospasm risk. However, repeat CT scanning is performed for several clinical indications that may require reassessment of the hemorrhage pattern. These include clinical deterioration, failure to improve as expected, suspicion of rebleeding, development of hydrocephalus, or post-procedural evaluation after aneurysm treatment. While the Fisher Grade itself is not formally reassigned on follow-up scans, the evolution of blood on serial imaging provides valuable clinical information. Clearance of subarachnoid blood over time generally correlates with decreasing vasospasm risk, while persistent or increased blood may indicate rebleeding or ongoing hemorrhage.
References
- Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by CT scanning. Neurosurgery. 1980;6(1):1-9
- Claassen J et al. Effect of cisternal and ventricular blood on risk of delayed cerebral ischemia after SAH. Stroke. 2001;32(9):2012-2020
- Frontera JA et al. Prediction of symptomatic vasospasm after SAH: the modified Fisher Scale. Neurosurgery. 2006;59(1):21-27
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy