Laboratory parameters of the 1st order – obligatory laboratory tests.
- Small blood count*
- Differential blood count* – to assess leukocyte (white blood cell) composition [neutrophil granulocytes: > 4,090/µl → indicating bacterial infection].
- Inflammatory parameters – CRP (C-reactive protein) or PCT (procalcitonin) if sepsis is suspected or ESR (erythrocyte sedimentation rate) [PCT ≥ 1.71 ng/ml → indication of bacterial infection]Note: In elderly patients, procalcitonin is suitable to map the prognosis and severity of pneumonia (pneumonia).
- Urine status (rapid test for: Nitrite, protein, hemoglobin, erythrocytes, leukocytes, urobilinogen) incl. sediment, if necessary urine culture (pathogen detection and resistogram, that is, testing of suitable antibiotics for sensitivity / resistance)Note: In febrile infants, the urine examination is mandatory.
- Electrolytes – chloride, sodium, potassium.
- Fasting glucose (fasting blood sugar)
Note: due tofever after a stay in the tropics or subtropics see below.
Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Renal parameters – urea, uric acid and creatinine.
- Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (γ-GT, gamma-GT; GGT); bilirubin; alkaline phosphatase.
- LDH
- Creatine kinase (CK)
- Total protein
- IgG, -M, -A and -E
- Protein electrophoresis in serum (synonym: serum electrophoresis).
- Coagulation parameters – PTT, Quick
- Thyroid parameters – TSH (thyroid stimulating hormone).
- Microbiological smears and / or cultures (aerobic and anaerobic blood cultures; 2 times 2 or better 3 times 2 blood cultures); if necessary, also from venous accesses or from drains.
- In cases of suspected intravascular infections such as endocarditis (blood culture almost always positive).
- Meningitis/ meningitis (sensitivity (percentage of diseased patients in whom the disease is detected by the use of the test, i.e., a positive test result occurs) approximately 60%).
- Pneumonia/pneumonia (sensitivity approx. 3-15%).
If necessary, also cultures of cerebrospinal fluid, stool or sputum; if necessary, skin and mucous membrane swabs.
- Infectiology
- Hepatitis Serology
- HIV, CMV, EBV, Lues Serology
- Tuberculosis diagnostics (tuberculin test, sputum, gastric juice, urine; see below tuberculosis).
- Immunological parameters (rheumatology).
- Rheumatoid factor (RF)
- ANA (antinuclear antibody; auto-Ak (IgG) against cell nuclear antigens) – due tocollagenoses (group of connective tissue diseases caused by autoimmune processes): systemic lupus erythematosus (SLE), polymyositis (PM) or dermatomyositis (DM), Sjögren’s syndrome (Sj), scleroderma (SSc) and Sharp’s syndrome (“mixed connective tissue disease”, MCTD).
- ANCA (anti-neutrophil cytoplasmic antibodies; auto-Ak against granulocyte cytoplasm) – e.g. due toGranulomatosis with polyangiitis (GPA; formerly Wegener’s granulomatosis), progressive glomerulonephritis, vasculitides, rheumatoid arthritis, autoimmune liver diseases and many more.
- Oncological diagnostics
- Blood smears, bone marrow biopsy – V. a. leukemia (blood cancer).
- Urinary catecholamines, NSE – V. a. neuroblastoma [children].
- Alpha-fetoprotein, β-HCG – V. a. germ cell tumors [children, adolescents]tumor markers depending on the suspected diagnosis.
- Stool analysis – occult blood (invisible blood); Calprotectin.
- Lymph node extirpation (lymph node removal) due toenlarged lymph nodes.
* Blood count changes due to infections.
| Normal leukocyte count | Brucellosis, malaria, syphilis (stage II), toxoplasmosis, circumscribed tuberculosis, sleeping sickness, |
| Left shift (increased occurrence of neutrophilic rod-nucleated granulocytes (rod-nucleated neutrophils) or their precursor cells in peripheral blood). | Infection (80% specificity/probability that actually healthy individuals who do not have the disease in question will also be identified as healthy in the test) |
| Leukocytosis(increase in the number of white blood cells) | Bacterial infections in general, amoebic liver abscess, miliary tuberculosis, rheumatic fever, sepsisCaution!
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| Leukopenia(decreased white blood cell count). | Viral diseasesBrucellosis, malaria, visceral leishmaniasis (synonyms: kala-azar; oriental bump; also known as dum-dum fever or black fever), typhoid fever, and paratyphoid fever, |
| Neutropenia(decrease in neutrophil granulocytes). | Brucellosis, malaria, visceral leishmaniasis (synonyms: kala-azar; oriental bump; also known as dum-dum fever or black fever) , tuberculosis |
| Toxic neutrophils | Bacterial infections (80% sensitivity) |
| Lymphocytosis(increase in the number of lymphocytes). | Epstein-Barr virus, cytomegalovirus, other viral diseasesBrucellosis, syphilis, toxoplasmosis, tuberculosis. |
| Monocytosis(increase in the number of monocytes). | Bacterial endocarditis, granulomatous disease, syphilis, tuberculosis, |
| Eosinophilia(increase in the number of eosinophilic granulocytes). | Bilharzia (schistosomiasis), acute Fasciola hepatica infection, filariasis (infection with parasitic nematodes), disseminated coccidioidomycosis, Katayama fever, muscular sarcocystosis, strongyloidiasis, trichinosisOther causes of eosinophilia include:
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| Eosinopenia(decrease in eosinophil granulocytes). | Typhoid abdominalis |
| Thrombocytopenia(decrease in platelets/platelets). | Acute HIV infection, dengue fever, Lyme disease, leptospirosis, malaria, rickettsiosis, sleeping sickness, sepsis, visceral leishmaniasis (in the setting of pancytopenia (synonym: tricytopenia; decrease in all three series of cells in the blood: leukocytopenia (decrease in white blood cells), anemia (anemia), and thrombocytopenia (decrease in platelets)) |
Fever after a stay in the tropics or subtropics
Laboratory parameters of the 1st order – obligatory laboratory tests.
- Blood test for plasmodia (see also under malaria)/microscopic examination of the thick drop and thin blood smears (direct detection of plasmodia)Specimen material should be collected during fever. Creating a “thick drop” (capillary blood)Note: Only a 3 times negative smear and “thick drop”, tested at intervals of 12-24 h each, excludes a fever patient with a high probability of malaria disease.
- Small blood count* [thrombocytopenia? ; see above].
- Differential blood count* [see above.]
- Inflammatory parameters – CRP (C-reactive protein) or PCT (procalcitonin) or ESR (erythrocyte sedimentation rate).
- Urine status (rapid test for: Nitrite, protein, hemoglobin, erythrocytes, leukocytes, urobilinogen) incl. sediment, if necessary urine culture (pathogen detection and resistogram).
- Fasting glucose
- Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH), and gamma-glutamyl transferase (γ-GT, gamma-GT; GGT).
- Renal parameters – creatinine, urea.
- Blood cultures
In case of clinical suspicion but negative microscopic findings, this examination must be repeated:
- Antigen detection with rapid tests – this can not replace the microscopic examination!
- Malaria PCR – only applicable in special cases, because very complex and expensive.
- Serological tests are useless in acute cases
Direct or indirect detection of “Plasmodium sp.” is reportable under the Infection Protection Act (IfSG). Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – if malaria diagnostics are negative.
- Blood, stool and urine cultures – especially to exclude typhoid and paratyphoid fever.
Further diagnostics according to concomitant symptoms and laboratory findings (see at the respective disease) (modified according to)
| Accompanying symptoms or findings | Possible diseases |
| Fever and exanthema (skin rash) |
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| Fever and splenomegaly (enlargement of the spleen). |
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| Fever and thrombocytopenia (lack of platelets). |
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| Fever and eosinophilia (increase in the number of eosinophilic granulocytes). |
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| Fever and transaminase elevation (levels of aspartate aminotransferase (abbreviated as GOT or AST) and/or alanine aminotransferase (abbreviated as GPT, ALAT, or ALT) elevated in the blood). |
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