More Details on Likelihood Ratios

Definition

The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.

How to Calculate LRs

We can assume that there are four possible groups of patients, as indicated (a,b,c,d) in the table below:

		Target Disorder
		Present	Absent
Diagnostic Test Result	+	a	b	a + b
	-	c	d	c + d
Totals		a + c	b + d	a + b + c + d

From these we can determine the sensitivity and specificity as follows:

Sensitivity = a/(a+c)
Specificity = d/(b+d)

We can now use these to calculate the likelihood ratio for a positive test result (LR+):
LR+ = sensitivity/(1-specificity)

Similarly, we can calculate the likelihood ratio for a negative test result (LR-):
LR- = (1-sensitivity)/specificity

Sample Calculation

Suppose you have a patient with anemia and a serum ferritin of 60 mmol/L. You come across a systematic review (J Gen Intern 1992; 7:145-53) of serum ferritin as a diagnostic test for iron deficiency anemia, with the results summarised as follows in the table:

		Target Disorder (iron deficiency anemia)
		Present	Absent
Diagnostic Test Result (serum ferritin)	+ (<65 mmol/L)	731 a	270 b	1001 a + b
	- (≥64 mmol/L)	78 c	1500 d	1578 c + d
Totals		a + c 809	b + d 1770	a + b + c + d 2579

These results indicate that 90% of the patients with iron deficiency anemia have a positive test result (serum ferritin < 65 mmol/L). This is known as the sensitivity and is calculated as:

Sensitivity = a/(a+c) = 731/809 = 90%

The results also show that 85% of patients who do not have iron deficiency anemia have a negative test result. This is referred to as the specificity, calculated as:

Specificity = d/(b+d) = 1500/1770 = 85%

From these the positive and negative likelihood ratios can be determined:

LR+ = sensitivity/(1-specificity) = 90%/15% = 6 LR- = (1-sensitivity)/specificity = 10%/85% = 0.12

Thus, from your calculation of LR+ you determine that your patient's positive test result would be about 6 times as likely to be seen in someone with iron deficiency anemia than in someone without the disorder.

Practice Calculation

The results of a blinded study (Stroke 1996;27:1516-20) assessing the use of plasma D-dimer levels for diagnosing deep venous thrombosis (DVT) in patients hospitalised for stroke rehabilitation are summarised in the table below. The presence or absence of DVT was determined by positive or negative venous duplex ultrasound results.

		Target Disorder (DVT)
		Present	Absent
Diagnostic Test Result (Plasma D-dimer level)	+ (>1591text{ng/mL})	13 a	19 b	32 a + b
	- (≤1591text{ng/mL})	1 c	72 d	73 c + d
Totals		a + c 14	b + d 91	a + b + c + d 105

What would the likelihood ratio for a positive test result (LR+) and the likelihood ratio for a negative test result (LR-) be?

LR+ = _______
LR- = _______

See our answer and compare

Sensitivity = a/(a+c) = 13/14 = 93%
Specificity = d/(b+d) = 72/91 = 79%
LR+ = sensitivity/(1-specificity) = 93%/21% = 4.4

How to Use LRs

The likelihood ratio is used to assess the value of a diagnostic test, sign or symptom. High likelihood ratios (e.g., LR>10) indicate that the test, sign or symptom can be used to rule in the disease, while low likelihood ratios (e.g., LR < 0.1) can rule out the disease. Likelihood ratios of around 1 indicate that no useful information for ruling the diagnosis in or out has been produced from the clinical findings.

Likelihood ratios can also be used to calculate the post-test probability for a disorder, which is another way to assess the value of a diagnostic test. For example, suppose you have a patient with anemia and prior to doing the serum ferritin test you think the chance that she has iron deficiency anemia is 50-50. Thus, her pre-test probability is 50%, which is equivalent to a pre-test odds of 1:1. You also determine that the likelihood ratio for a positive serum ferritin test result is 6 (see Sample Calculation above). The post-test probability can now be calculated as follows:

post-test odds = 1 x 6 = 6
post-test probability = 6/(6+1) = 86%

The serum ferritin test is performed and your patient is found to have a serum ferritin concentration of 60 mmol/L. The increase in probability from 50% (pre-test) to 86% (post-test), suggests that the serum ferritin test is useful for determining whether or not your patient has iron deficiency anemia.

Examples

Criteria for Inclusion of Examples

(Modified from criteria used by ACP Journal Club)

1. Inclusion of an appropriate spectrum of patients - both those with and without the target disorder of interest.

2. Interpretation of diagnostic standard without knowledge of the test result.

3. Interpretation of the test without knowledge of the diagnostic standard result.

4. Each person must receive the new test and the diagnostic standard use of an objective criterion standard measure of diagnosis or current clinical standard for diagnosis.

Tables of Examples

Target Disorder	Sign, Test, Symptom	Reference Standard	Patient, Population, Setting	LR+ (95% CI)
Dementia1	Mini-Mental Status Examination(MMSE) score at the 26/27 cut-off point	Diagnosis of dementia and depression made by senior psychiatrists using a checklist of DSM-III-R criteria	Patients admitted to a university geriatric hospital or outpatient memory clinic in Switzerland	2.5
Deep Venous Thrombosis (DVT)2	Plasma D-dimer level > 1092 ng/mL	Venous duplex ultrasonography (VDU)	Patients hospitalised in a stroke rehabilitation unit in the US	3.1
Group A?b-haemolytic streptococcus (GABHS) pharyngitis3	Positive rapid streptococcal antigen detection test	Throat culture	Patients with sore throat presenting to general practices in the Netherlands	15.2
Proximal DVT4	Ultrasonography	Venography	Symptomatic patients	47.5
DVT4	Ultrasonography	Venography	Asymptomatic patients	7.8
Alzheimers Disease (AD)5	Positive apolipoprotein E (APOE) genotype test	Criteria from the National Institute of Neurological Disorders & stroke or the DSM-III-R	Patients referred for evaluation of dementia in AD centres in US	2
Peripheral vascular disease6	Unilateral cool limb	Ankle-to-arm systolic pressure index	Systematic review of 17 studies	5.8
Arterial stenosis6	Limb bruit	Ankle-to-arm systolic pressure index	Systematic review of 17 studies	3.2
Myocardial Infarction (MI)7	Any ST-segment elevation on an ECG	Diagnosis of MI based on World Health Organization (WHO) criteria = confirmation by ECG and lab test results	Adult patients with chest pain	11.2
Myocardial Infarction7	Radiation of pain to both arms	Diagnosis of MI based on WHO criteria	Adult patients with chest pain	7.1
Myocardial Infarction7	New conduction defect	Diagnosis of MI based on WHO criteria	Adult patients with chest pain	6.3

Target Disorder	Sign, Test, Symptom	Reference Standard	Patient, Population, Setting	LR+ (95% CI)	LR- (95% CI
Deep venous thrombosis (DVT) 8	Compression ultrasound (USS) in all patients	Venography	Hospital patients	39	0.23
	USS in high risk	Venography	Hospital patients	∞	0.09
	USS in moderate risk	Venography	Hospital patients	53	0.39
	USS in low risk*	Venography	Hospital patients	24	0.34
DVT9	Homan's sign (positive if no dorsiflexion of the foot on squeezing the calf muscles)		Hospital patients	1.5	0.6
Adult meningitis10	Jolt accentuation of headache	Lumbar puncture or autopsy	Patients presenting to outpatient or emerg. dept. with headache and fever; n=30, all with objectively confirmed meningitis	2.2	0
Abdominal aortic aneurysm (AAA)11	Abdominal palpation; AAA ≥ 3.0cm	Ultrasound	Systematic review; 15 studies of patients not previously known to have AAA	12.0 (7.4-19.5)	0.72 (0.65-0.81)
AAA11	Abdominal palpation; ≥ 4.0cm	Same as above	Same as above	15.6 (8.6-28.5)	0.51 (0.38-0.67)
Ascites12	Fluid wave	Abdominal ultrasound	Inpatients veteran with evidence of liver disease examined by internists	9.6	0.2
Postnatal depression13	Number of routine and non-routine contacts had by general practitioners (GPs), health visitors (HVs), midwives (Ms) and whole primary healthcare teams (WPHTs) with mothers 42 days after delivery and whether or not they were aware of postnatal depression in the mother. Sensitivity and specificity for detecting postnatal depression were also measured.	The Edinburgh Postnatal Depression Scale (EPDS) score > 11	Mothers who attended their postnatal examination at 6-8 weeks after delivery. Set in 7 general practices in Bolton, UK.	GPs: 8.06	GPs: 0.70
				HVs: 3.04	HVs: 0.86
				Ms: 12.42	Ms: 0.80
				WPHTs: 5.27	WPHTs: 0.62
Myocardial Infarction (MI)14	Cardiac-specific troponin T (cTnT) was measured using a handheld device containing specific monoclonal antibodies and was read by a clinical chemistry technologist blinded to the other test results at two different times.	Clinical evaluation, ECG readings, CK and CK-MB quantitative assays or autopsy results by a blinded observer	Patients presenting to the hospital with chest pain suggestive of MI. Set in a coronary care and telemetry unit of a tertiary care university medical center	At 0-2 hours: 6.3	At 0-2 hours: 0.8
				At >8 hours: 6.0	At >8 hours: 0.15
Deep venous thrombosis (DVT)15	D-dimer analysis alone	Duplex ultrasound scanning	Patients with suspected DVT. Set in a university hospital in Basel, Switzerland.	2.0	0.3
	D-dimer analysis plus clinical assessment			1.8	0.09
Abdominal aortic aneurysm (AAA)16	Abdominal palpation during physical examination	Ultrasound	Half of the patients had AAA, half did not (determined by previous ultrasound)	2.7	0.43
Depression in elderly people17	15 item Geriatric Depression Scale (GDS)	Schedules for Clinical Assessment in Neuropsychiatry to make ICD-10 (criteria for mood disorders) diagnoses	Patients were ≥75 years of age, were not in residential care and had completed the diagnostic interview after completing the GDS 15. Set in a large general practice in Leicestershire, UK	Depression: 4.3	Depression: 0.2
				Anxiety: 3.4	Anxiety: 0.4
Depression in elderly patients18	Even Briefer Assessment Scale for Depression (8 questions on depressive mood, worries, suicidal thoughts and vegetative symptoms)	Diagnoses made by a psychiatrist or psychiatric nurse who used the Feighner criteria	Patients were ≥65 years of age. Set in an old age home, a day clinic and a psychiatric hospital in Germany	6.2	0.8
Deep Venous Thrombosis (DVT) in symptomatic patients19	D-dimer analysis	All DVT	Patients with suspected DVT at a university hospital in Switzerland	2.0	0.3
Predicting ectopic pregnancy20	Clinical prediction guide: High risk women had signs of peritoneal irritation or definite cervical motion tenderness. Intermediate risk women had no fetal heart tones by handheld Doppler, no tissue visible at the cervical os and pain or tenderness	High risk	Women who were haemodynamically stable and had abdominal pain or vaginal bleeding in the first trimester of pregnancy	6.1	0.7
		Intermediate risk		1.4	0.0
Helicobacter pylori infection21	13C-Urea blood test (13C-UBT - patients received 125 mg dissolved in 75 ml of water)	Positive test for histologic testing	Patients (mean age 49 y, 51% men) who were referred for endoscopy at 5 medical centers in the United States	19.9	0.1
	Rapid urease testing (RUT)			19.4	0.1
	13C-UBT	Positive test for histologic testing and positive RUT		10.4	0.1
	13C-UBT	Positive test for histologic testing or positive RUT		44.0	0.1
Symptomatic DVT22	D-dimer levels were assessed using a rapid whole blood assay (SimpliRed)	Duplex ultrasono-graphy scanning (DUS)	High risk for DVT based on clinical assessment score that included data on the presence of cancer, immobilization, localized tenderness, history of leg trauma, unilateral edema or erythema, dilated superficial veins and hospitalization	1.9	0.0
			Patients at moderate risk for DVT	3.4	0.3
			Patients at low risk for DVT	7.5	0.3
Colorectal polyps and cancer 23	Virtual colonoscopy	Conventional colonoscopy done using a standard endoscope	Adults aged 50 to 77 years of age at a high risk of colorectal neoplasia (≥ 50 y of age, with a history of adenomatous polyps, recent sigmoidoscopic evidence of ³ 1 polyp, a positive finding on fecal occult-blood testing or a history of colorectal cancer in ≥ 1 first-degree relatives)	5.0	0.2
Urinary tract infection in children24	Uriscreen test	Quantitative urine culture, done using the commercial Diaslide method	Random sample of 121 children (1 month to 17 years of age) who presented at the emergency department with symptoms of UTI at a children's hospital in Israel.	3.2	∞
	Dipstick test (Multistix 10 SG strip)			5.6	0.03
	Urinalysis done in the hospital laboratories with an automated urine analyzer			7.6	0.13
Helicobacter pylori infection25	Near-patient test (FlexSure) testing serum from a clotted sample	Enzyme-linked immuno-sorbent assay (ELISA)	Patients aged from 18 to 73 years of age and had symptoms of dyspepsia of sufficient severity to justify empiric treatment with H2-antagonists or proton-pump inhibitors.	32.4	0.3
Pneumonia in children26	Tachypnea (defined as a respiratory rate > 60 breaths per minute in children < 2 months of age, > 50 breaths per minute in children 2 to 12 months of age and > 40 breaths per minute in children≥1 year of age)	Chest Radiography	110 children who were 3 days to 5 years of age and had acute respiratory infection	2.2	0.4
			Children with disease duration < 3 days	1.5	0.7
			Children with disease duration 3 to 5 days	1.9	0.5
			Children with disease duration ≥ 6 days	3.4	0.1
	Clinical judgment		All children	1.7	0.5
Hypoxia in infants27	Respiratory rate was counted for 1 minute while observing the infants chest and abdominal movements when the infant was quiet.	Assessment of oxygen saturation (measured at the finger or toe with a pulse oximeter). Hypoxia was defined as an oxygen saturation level ≤ 90%	Infants who were < 2 months of age and had symptoms of any acute illness and whose respiratory rate was ≥ 40 breaths/min	2.2	0.4
			≥ 50 breaths/min	2.2	0.2
			≥ 60 breaths/min	2.5	0.3
			≥ 70 breaths/min	3.3	0.6
			≥ 80 breaths/min	3.4	0.8
Polyneuro-pathy in type 2 diabetes mellitus28	Patients completed a 34-item diabetes symptom checklist that measured the physical and psychological symptoms related to type 2 diabetes	Clinical neurologic examination done by a trained research clinician who was blinded to the results of the checklist	Patients with type 2 diabetes mellitus who received care in general practice who were < 68 years of age	4.0	0.77
			≥ 68 years of age	2.75	0.85
Pathologic findings in the common bile duct (CBD)29	Abnormal findings on biliary scintigraphy	Endoscopic or preoperative cholangio-graphy	75 consecutive patients with symptomatic gallstone disease at a tertiary referral center in Bombay, India	15	0.07
	Pathologic findings in the common bile duct (CBD) Abnormal findings on biliary scintigraphy CBD > 9mm with ultrasonography			∞	0.4
	CBD stone with ultrasonography			∞	0.5
	Abnormal bile duct with ultrasonography			17	0.3
	All standard criteria combined			1.7	0.23
	Modified standard criteria			3	0.2
	Ultrasonography and scintiscan			78	0.04
Neonatal jaundice30	Clinical examination - infants were observed by 2 clinicians under fluorescent lighting near a window. Clinicians assessed jaundice as being absent, slight or obvious for prespecified body zones	Serum bilirubin test	122 healthy full-term infants (mean age 2 days, 54% boys)	1.9	0.15
Assessing left ventricular systolic dysfunction31	Physical examination, chest radiography, echocardiography, supine 12-lead electrocardio-graphy, blood pressure measurements and blood tests	Left ventricular systolic dysfunction was defined as an ejection fraction of < 0.45 and was determined from videotapes and photoecho-cardiograms by an investigator blinded to the other clinical data	Patients with abnormal electrocardio-graphic results	1.96	0.24
			Patients with N-terminal atrial natriuretic peptide level > 0.8 nmol/L	3.82	0.62
			Patients with heart rate > diastolic pressure	3.91	0.55
Chronic obstructive airway disease (COAD) in adults32	Spirometry was done within 30 minutes of clinical examination with the better attempt of 2 efforts recorded	COAD confirmed if FEV1 and FEV1:FVC ratio were < 5th percentile	Patients were recruited so that approximately one-third had confirmed OAD, one-third had suspected OAD and one-third had no evidence of OAD	Self reported history of OAD: 7.3	Self reported history of OAD: 0.5
				Smoking >40 pack per year: 8.3	Smoking >40 pack per year: 0.8
				Age ≥45 years: 1.3	Age ≥45 years: 0.4
				Maximum laryngeal height ≤ 4cm: 2.8	Maximum laryngeal height ≤ 4cm: 0.8
				All factors present: 221	All factors present: 0.13
Abdominal aortic aneurysm (AAA)33	Abdominal palpations	Ultrasonograpgy	Patients were between the ages of 51 and 88 and had known AAAs (≥3cm in diameter) or had known absence of AAAs	All examinations: 2.7	All examinations: 0.43
				Girth <100cm: 2.5	Girth <100cm: 0.14
				Girth ≥100cm: 3.2	Girth ≥100cm: 0.56
				Abdomen not obese: 2.6	Abdomen not obese: 0.17
				Abdomen obese: 2.9	Abdomen obese: 0.64
				Abdomen not tight: 2.3	Abdomen not tight: 0.38
				Abdomen tight: 4.7	Abdomen tight: 0.54
				Aorta palpable: 2.0	Aorta palpable: 0.22
				Girth ≥100cm and aorta palpable: 2.0	Girth ≥100cm and aorta palpable: 0.30
Psychiatric disorders34	Quick PsychoDiagnostics Panel (automated test that patients complete by answering true/false questions)	Structured Clinical Interview for DSM-IV diagnoses	HMO patients referred by their physicians or self-referred for a first time mental health consultation and were not receiving mental health treatment at study entry	Major depression: 20.3	Major depression: 0.2
				Generalised anxiety disorder: 7.9	Generalised anxiety disorder: 0.2
				Panic disorder: 23.7	Panic disorder: 0.3
				Obsessive compulsive disorder: 23.0	Obsessive compulsive disorder: 0.3
Benzodiazepine dependence35	Severity of Dependence Scale	Composite International Diagnostic Interview	Participants were 18-75 years of age (75% women), had neurotic diagnosis, continuously used benzodiazepine daily for ≥ 3 months and had a stable maintenance dose of their benzodiazepine equivalent to 5-50 mg/day of diazepam	17	0.02
Urinary tract infection36	Visual inspection of urine samples	Laboratory urinalysis including dipstick testing for presence of nitrites and leukocyte esterase, bacteria on microscopy and white cell count	Healthy patients< 21 years of age (77% girls) who had either a catheterised or midstream urine specimen collected for urine culture at an emergency department of a children's hospital in Cincinnati, Ohio, USA	All specimens: 5.07	All specimens: 0.13
				Cathetrised specimens: 6.04	Cathetrised specimens: 0.19
				Midstream specimens: 4.52	Midstream specimens: 0.07
Mild dementia in older people37	Hopkins Verbal Learning Test	DSM-IV criteria	56 patients (mean age 75 years, 63% women, mean education 8.5 years)	4.80	0.05
	Mini-Mental State Examination	DSM-IV criteria		12.75	0.13
Detecting hypoxia in sick infants38	Measurements of SpO2 and partial pressure of oxygen in arterial blood in order (PaO2 <6 kPa indicated hypoxemia)	Partial pressure of oxygen in arterial blood (PaO2)	Infants who required arterial lines at a neonatal intensive care unit in Liverpool, UK	Lower limit for SpO2: 88%: 1.43 89%:1.24 90%: 1.57 91%: 1.64 92%: 1.57 93%: 1.38 94%: 1.33 Individualised: 1.26	Lower limit for SpO2: 88%: 0.87 89%:0.88 90%: 0.69 91%: 0.50 92%: 0.419 3%: 0.41 94%: 0.33 Individualised: 0.69
Detecting hyperoxia in sick infants39	Measurements of SpO2 and partial pressure of oxygen in arterial blood in order (PaO2 >10 kPa indicated hyperoxemia)	Partial pressure of oxygen in arterial blood(PaO2)	Infants who required arterial lines at a neonatal intensive care unit in Liverpool, UK	Upper limit for SpO2: 94%:1.37 95%: 1.67 96%: 1.95 97%: 5.25 98%: 0.79 Individualised: 2.08	Upper limit for SpO2: 94%: 0 95%: 0 96%: 0.34 97%: 0.63 98%: 1.03 Individualised: 0.39
Mild dementia in older persons40	The Hopkins Verbal Learning Test	DSM-IV criteria	56 patients (mean age 75 y, 63% women) participated at a geriatric psychiatric hospital in Australia	4.80	0.05
	Mini-Mental State Examination			12.57	0.13
Acute pulmonary embolism (PE)41	Dual-section helical computed tomography done in a caudocranial direction	Pulmonary digital subtraction arteriography	Patients were 18 to 75 years of age and had clinically suspected acute PE at a hospital radiology department in Boulogne, France	29.1	0.05
Dementia42,43	Clock drawing test	NINCDS-ADRDA criteria	Elderly patients	9.6	0.4
Cirrhosis44	Encephalopthy	Needle biopsy of liver	Patients with severe chronic active liver disease	17.5	0.7
Anemia45	Facial pallor	Hematocrit <35%, hemoglobin <11g/dl, or hemoglobin <11 g/dl in women and <13g/dl in men	Patients were selected so that there was equal representation in five hematocrit categories	3.8	0.6
	Nail bed pallor			1.7	0.6
	Palmar pallor			2.5	0.5
Hypovolemia46	Dry axilla	Elevated serum urea nitrogen-creatinine ratio, osmolarity, or sodium level	Patients were above the age of 70and were consecutively admitted with acute medical conditions	2.8	Not significant
Detection of fever47	Patients' report of fever	Measured temperature >38? C	Ambulatory adult patients in a military tertiary care emergency department	4.9	0.2
Pulmonary embolism48,49	Risk factors - known cancer	Positive pulmonary angiogram	Patients suspected of having a pulmonary embolism	4.1	0.8
	Heart rate >90/min			1.8	0.3
	Respiratory rate >20/min			1.7	0.5
	Calf pain or swelling			2.6	0.6
Congestive Heart Failure50,51,52,53,54	Elevated Venous Pressure at the bedside - Detecting central venous pressure (CVP) > 8 cm H2O	Measurement by catheter in supine position using method of Lewis	Patients having cardiac catheterization were studied	9.0	Not significant
	Elevated Venous Pressure at the bedside - Detecting (CVP) > 12 cm H2O			10.4	0.1
	Positive abdominojugular test - detecting elevated left heart diastolic pressures	Pulmonary capillary wedge pressure >15 mm Hg or left ventricular end diastolic pressure >15 mm Hg		8.0	0.3
Cardiomegaly55	Dullness extends more than 10.5 cm from midsternal line, patient supine - detecting cardiothoracic ratio >0.5	Maximal transverse diameter of heart on chest radiography divided by maximal transverse diameter of thoracic cage	Patients had a posteroanterior radiograph of the chest	2.5	0.05
Stenosis56,57	Hyperkinetic apical movement - detecting associated mitral regurgitation or aortic valve disease in patients with mitral stenosis	Aortic valve area < 0.75 cm, <0.8 cm, <0.9 cm; peak gradient >50 mm Hg; or peak gradient velocity of aortic flow >3.6 m/sec	Patients with cardiovascular problems	11.2	0.3
	Sustained apical movement - detecting severe aortic stenosis in patients with aortic flow murmurs			4.1	0.3
Third Hear Sound58,59	Detecting ejection fraction less than 0.3	Radionucleotide left ventricular ejection fraction <0.3	Patients with suspected or proved coronary heart disease who underwent radionucleotide angiography or ventriculography	4.1	0.3
Systolic Murmurs60,61	Changing venous return - louder with Valsalva strain - detecting hypertrophic cardiomyopathy	Doppler echocardiography or angiography	Patients with systolic murmur of Grade I/VI or higher	14.0	0.3
	Changing venous return - louder with squatting-to-standing - detecting hypertrophic cardiomyopathy			6.0	0.1
	Changing venous return - softer with passive leg elevation - detecting hypertrophic cardiomyopathy			9.0	0.1
	Changing systematic vascular resistance (afterload) - softer with isometric hand grip-detecting hypertrophic cardiomyopathy			3.6	0.1
	Changing systematic vascular resistance (afterload) - louder with isometric hand grip - Detecting mitral regurgitation or ventricular septa defect			5.8	0.3
	Changing systematic vascular resistance (afterload) - louder with transient arterial occlusion - Detecting mitral regurgitation or ventricular septa defect			48.7	0.2
Severe Aortic Stenosis62,63	Arterial pulse-reduced carotid artery volume	Aortic valve area < 0.75cm, < 0.8 cm, < 0.9 cm; peak gradient > 50 mm Hg; or peak gradient velocity of aortic flow > 3.6 m/sec	Patients with suspected aortic stenosis	2.3	0.3
	Apical impulse-sustained apical impulse			4.1	0.3
Splenic Enlargement64,65,66	Splenic percussion signs - detecting enlarged spleen - Spleen percussion sign (Castell's)	Spleen enlarged by ultrasonography, scintigraphy or postmortem weight >200g or >250g	Patients who underwent splenic ultrasonography or scintigraphy	1.9	0.7
Ascites67,68,69	Inspection-bulging flanks	Peritoneal fluid by ultrasonography	Patients suspected of having ascites	1.9	0.4
	Inspection-edema			3.8	0.2
	Palpation and percussion-flank dullness			Not significant	0.3
	Palpation and percussion-shifting dullness			2.3	0.4
	Palpation and percussion-fluid wave			5.0	0.5
Carpal Tunnel Syndrome70	Hand diagram"classic" or "probable"	Abnormal motor or sensory conduction within the carpal tunnel, measured by nerve conduction testing	Patients presenting with upper extremity discomfort were evaluated	2.4	0.5
	Hand diagram-"unlikely"			0.2	---

PMNs in Ascitic Fluid	Spontaneous Bacterial Peritonitis71 (based on reference standard)		LR (Likelihood Ratio)
	Present (n%)	Absent (n%)
>1000	33 g(g/a+c+e+g)	10 h(h/b+d+f+h)	22.3
501-1000	2 e(e/a+c+e+g)	5 f(f/b+d+f+h)	22.3
251-500	2 c(c/a+c+e+g)	12 d(d/b+d+f+h)	1.14
0-250	3 a(a/a+c+e+g)	245 b(b/b+d+f+h)	0.08
Totals	40 a+c+e+g (100%)	272 b+d+f+h (100%)

Note regarding DVT

Target Disorder	Clinical Features (History and examination can help decide about further tests, but cannot rule out DVT)	Score
Deep venous thrombosis (DVT)	Active cancer (on-going treatment, or diagnosed within 6/12 or palliative care)	1
	Paresis, paralysis or recent plaster-cast immobilisation of lower extremity	1
	Recently bed-ridden>3 days &/or major surgery< 4/52	1
	Localised tenderness over distribution of deep veins	1
	Entire leg swollen	1
	Calf swelling 3cm>symptomless side, measured at 10cm below tibial tubercle	1
	Pitting oedema symptomatic leg only	1
	Collateral superficial veins (non-varicose)	1
	Alternative diagnosis as likely or greater than that of DVT	-2

The resulting score places the patient into one of three risk groups:

Score	Risk	LR
0 or less	low	0.16
1 or 2	moderate	1.0
3 or more	high	16

Further tests (such as a compression ultrasound) can then be used to rule DVT in or out.

References