Pneumonia diagnostic algorithm

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Alejandro Lemor, M.D. [3]

Pneumonia Microchapters


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Differentiating Pneumonia from other Diseases

Epidemiology and Demographics

Risk Factors


Natural History, Complications and Prognosis


Diagnostic Criteria

Diagnostic Algorithm

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Diagnostic Algorithm

Shown below is an algorithm for the diagnostic approach of pneumonia.[1][2]
Abbreviations: HCAP: Healthcare-associated pneumonia; CAP: Community-acquired pneumonia; VAP: Ventilator-associated pneumonia; HAP: Hospital-acquired pneumonia; AMT: Abbreviated mental test score

Symptoms that suggest a lower respiratory tract infection:
Cough with sputum
Pleuritic chest pain
Order Labs:
Complete blood count (CBC)
Blood urea nitrogen (BUN)
Sputum gram stain and culture
Blood culture and ABG if necessary
If atypical pneumonia is suspected, obtain:
❑ Urine legionella antigen, rapid influenza test
Enyzme Immunoassay
Polymerase chain reaction (PCR) for atypical and viral including influenza
❑ Order a chest X-ray if the patient presents with any of the following:[3]
Does the patient meets any of the following criteria for HCAP?[4]
  • Hospitalized in an acute care hospital for 2 or more days within 90 days of the infection;
  • Resided in a nursing home or long-term care facility;
  • Received recent intravenous antibiotic therapy, chemotherapy, or wound care within the past 30 days of the current infection;
  • Attended a hospital or hemodialysis clinic
The patient has CAP
Does the infection occurred ≥48 hours after admission and it was not present at admission?
Does the patient has at least 2 of the following CURB65 criteria?
  • Confusion (AMT ≤8)
  • Urea greater than 7 mmol/l (BUN > 20)
  • Respiratory rate ≥ 30 breaths/min
  • Blood pressure ≤ 90 systolic or ≤ 60 diastolic
  • Age 65 or older

If the patient had an endotracheal tube placed ≥48 hours ago, suspect VAP. Otherwise, the patient has HAP

The patient has HCAP

Admit the patient and administer empiric inpatient antibiotic regimen

CURB-65 Clinical Prediction Rule

CURB-65 is a clinical prediction rule that has been validated for predicting mortality in community-acquired pneumonia[5] and infection of any site[6]. The CURB-65 is based on the earlier CURB score[7] and is recommended by the British Thoracic Society for the assessment of severity of pneumonia.[8]

Calculation of CURB-65

The score is an acronym for each of the risk factors measured. Each risk factor scores one point, for a maximum score of 5:

Criteria Score
Confusion (defined as an AMT of 8 or less) 1
Urea greater than 7 mmol/l (Blood Urea Nitrogen > 20) 1
Respiratory rate of 30 breaths per minute or greater 1
Blood pressure less than 90 systolic or diastolic blood pressure 60 or less 1
Age 65 or older 1

Interpretation of CURB-65: Risk of Death from Pneumnoia

The risk of death increases as the score increases.

CURB-65 Score Risk of death
0 0.7%
1 3.2%
2 13.0%
3 17.0%
4 41.5%
5 57.0%

The CURB-65 has been compared to the pneumonia severity index in predicting mortality from pneumonia.[9]

Interpretation of CURB-65: Risk of Death from any Infection

A cohort study of patients with any type of infection (half of the patients had pneumonia), the risk of death increases as the score increases[6]:

  • 0 to 1 <5% mortality
  • 2 to 3 < 10% mortality
  • 4 to 5 15-30% mortality

Infectious Diseases Society of America/American Thoracic Society Consensus Recommendation Criteria for Severe Community Acquired Pneumonia in Adults

The IDSA criteria are used to asses if a patient with community-acquired pneumonia requires ICU admission. Patients with at least one major criteria or ≥ 2 minor criteria should be admitted to the ICU.[10]

Major Criteria

Minor Criteria

Clinical Prediction Rule for Predicting Pulmonary Infiltrates Based on Clinical Findings

A clinical prediction rule found the five following signs from the medical history and physical examination best predicted infiltrates on the chest radiograph of 1134 patients presenting to an emergency room:[11]

Probability of an Infiltrate
Based on the Number of Findings
Number of Findings Primary Care Emergency Room
5 47% 75%
4 27 56
3 8 22
2 4 11
1 1 3
0 1 2

Pneumonia Severity Index (PSI)

The pneumonia severity index (PSI), also known as PORT score, is a clinical prediction rule that medical practitioners can use to calculate the probability of morbidity and mortality among patients with community acquired pneumonia.[12]

Development of the PSI

The rule uses demographics (whether someone is older, and is male or female), the coexistence of core morbid illnesses, findings on physical examination and vital signs, and essential laboratory findings. This study demonstrated that patients could be stratified into five risk categories, Risk Classes I-V, and that these classes could be used to predict 30-day survival.

Data Source for Derivation and Validation

The rule was derived then validated with data from 38,000 patients from the MedisGroup Cohort Study for 1989, comprising 1 year of data from 257 hospitals across the US who used the MedisGroup patient outcome tracking software built and serviced by Mediqual Systems (Cardinal Health). One significant caveat to the data source was that patients who were discharged home or transferred from the MedisGroup hospitals could not be followed at the 30-day mark, and were therefore assumed to be "alive" at that time. Further validation was performed with the Pneumonia Patient Outcomes Research Team [PORT] (1991) cohort study. This categorization method has been replicated by others[9] and is comparable to the CURB-65 in predicting mortality.[9]

Usage and Application of the PSI

The purpose of the PSI is to classify the severity of a patient's pneumonia to determine the amount of resources to be allocated for care. Most commonly, the PSI scoring system has been used to decide whether patients with pneumonia can be treated as outpatients or as (hospitalized) inpatients. A Risk Class I pneumonia patient can be sent home on oral antibiotics. A Risk Class II-III pneumonia patient may be sent home with IV antibiotics or treated and monitored for 24 hours in hospital. Patients with Risk Class IV-V pneumonia patient should be hospitalized for treatment.

Calculation of PSI

The PSI Algorithm is detailed below. An online, automated PSI calculator is available on the US AHRQ website.

Step 1

Does the patient have any of the following conditions?

Risk Class I
Step 2
Assess the following conditions and assign the corresponding scores:
Condition Points
If Male+Age (yrs)
If Female+Age (yrs) - 10
Nursing home resident +10
Neoplastic disease +30
Liver disease +20
Congestive heart failure +10
Cerebrovascular disease +10
Renal disease +10
Altered mental status+20
Pulse ≥125/minute +20
Respiratory rate >30/minute +20
Systolic blood pressure ≥90 mm Hg +15
Temperature <35°C or ≥40°C +10
Arterial pH <7.35 +30
Blood urea nitrogen ≥30 mg/dl (9 mmol/liter) +20
Sodium <90 mmol/liter +20
Glucose ≥250 mg/dl (14 mmol/liter)+10
Hematocrit <30%+10
Partial pressure of arterial O2 <60mmHg +10
Pleural effusion +10
∑ <70 = Risk Class II
∑ 71-90 = Risk Class III
∑ 91-130 = Risk Class IV
∑ >130 = Risk Class V

PSI Derivation and Validation Data

Medisgroup Study (1989) PORT Validation Study (1991) Cohort
Derivation Cohort Validation Cohort Inpatients Outpatients All Patients
Risk Class no. of pts % died no. of pts % died no. of pts % died no. of pts % died no. of pts % died
I 1,372 0.4 3,034 0.1 185 0.5 587 0.0 772 0.1
II (<70) 2,412 0.7 5,778 0.6 233 0.9 244 0.4 477 0.6
III (71–90) 2,632 2.8 6,790 2.8 254 1.2 72 0.0 326 0.9
IV (91–130) 4,697 8.5 13,104 8.2 446 9.0 40 12.5 486 9.3
V (>130) 3,086 31.1 9,333 29.2 225 27.1 1 0.0 226 27.0
Total 14,199 10.2 38,039 10.6 1343 8.0 944 0.6 2287 5.2

Note: % Died refers to 30-day mortality.

Hospital Acquired Pneumonia

Shown below is an algorithm for the diagnostic approach of Healthcare-associated pneumonia (HCAP), Ventilator-associated pneumonia VAP), and Hospital-acquired pneumonia (HAP).[13]

High suspicion of HAP, VAP or HCAP
Obtain sputum or respiratory secretions sample for culture and microscopy
Does the patient has any of the following risk factors for MDR infection?
  • Antimicrobial therapy in preceding 90 days
  • Current hospitalization of ≥ 5 days
  • High frequency of antibiotic resistance in the community or in the specific hospital unit
  • Immunosuppressive disease and/or therapy
  • Presence of risk factors for HCAP:
  • Hospitalization ≥2 days in the preceding 90 days
  • Residence in a nursing home or extended care facility
  • Home infusion therapy (including antibiotics)
  • Chronic dialysis within 30 days
  • Home wound care
  • Family member with multidrug-resistant pathogen
Start empirical therapy with combined broad spectrum antibiotics
Click here for more detail
Start empirical therapy with limited spectrum antibiotics
Click here for more detail
After 2-3 days, check cultures and assess the clinical response based on:
Does the patient improved his clinical status after 48-72 hours?
Assess culture results
Assess culture results
Positive Culture
Negative Culture
Positive Culture
Negative Culture
De-escalate antibiotics, treat for 7-8 more days and re-evaluate
Consider stopping antibiotics
Adjust antibiotic regimen based on culture susceptibility, look for other infection sites and complications
Look for other pathogens, infection sites and complications


  1. Mandell, L. A.; Wunderink, R. G.; Anzueto, A.; Bartlett, J. G.; Campbell, G. D.; Dean, N. C.; Dowell, S. F.; File, T. M.; Musher, D. M.; Niederman, M. S.; Torres, A.; Whitney, C. G. (2007). "Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults". Clinical Infectious Diseases. 44 (Supplement 2): S27–S72. doi:10.1086/511159. ISSN 1058-4838.
  2. Solomon, Caren G.; Wunderink, Richard G.; Waterer, Grant W. (2014). "Community-Acquired Pneumonia". New England Journal of Medicine. 370 (6): 543–551. doi:10.1056/NEJMcp1214869. ISSN 0028-4793.
  3. Watkins RR, Lemonovich TL (2011). "Diagnosis and management of community-acquired pneumonia in adults". Am Fam Physician. 83 (11): 1299–306. PMID 21661712.
  4. Attridge RT, Frei CR (2011). "Health care-associated pneumonia: an evidence-based review". The American Journal of Medicine. 124 (8): 689–97. doi:10.1016/j.amjmed.2011.01.023. PMID 21663884. Retrieved 2012-09-02. Unknown parameter |month= ignored (help)
  5. Lim WS, van der Eerden MM, Laing R; et al. (2003). "Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study". Thorax. 58 (5): 377–82. PMID 12728155.
  6. 6.0 6.1 Howell MD, Donnino MW, Talmor D, Clardy P, Ngo L, Shapiro NI (2007). "Performance of severity of illness scoring systems in emergency department patients with infection". Academic emergency medicine : official journal of the Society for Academic Emergency Medicine. 14 (8): 709–14. doi:10.1197/j.aem.2007.02.036. PMID 17576773.
  7. Lim WS, Macfarlane JT, Boswell TC; et al. (2001). "Study of community acquired pneumonia aetiology (SCAPA) in adults admitted to hospital: implications for management guidelines". Thorax. 56 (4): 296–301. PMID 11254821.
  8. "BTS Guidelines for the Management of Community Acquired Pneumonia in Adults". Thorax. 56 Suppl 4: IV1–64. 2001. PMID 11713364.
  9. 9.0 9.1 9.2 Aujesky D, Auble TE, Yealy DM; et al. (2005). "Prospective comparison of three validated prediction rules for prognosis in community-acquired pneumonia". Am. J. Med. 118 (4): 384–92. doi:10.1016/j.amjmed.2005.01.006. PMID 15808136.
  10. Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG (2007). "Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults". Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America. 44 Suppl 2: S27–72. doi:10.1086/511159. PMID 17278083. Retrieved 2012-09-06. Unknown parameter |month= ignored (help)
  11. Heckerling PS, Tape TG, Wigton RS; et al. (1990). "Clinical prediction rule for pulmonary infiltrates". Ann. Intern. Med. 113 (9): 664–70. PMID 2221647.
  12. Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997 Jan 23;336(4):243–250. PMID 8995086
  13. "Guidelines for the Management of Adults with Hospital-acquired, Ventilator-associated, and Healthcare-associated Pneumonia". American Journal of Respiratory and Critical Care Medicine. 171 (4): 388–416. 2005. doi:10.1164/rccm.200405-644ST. ISSN 1073-449X.