CRP and Procalcitonin

Question 1

CRP method (Siemens Atellica)

Answer 1

Latex-enhanced immunoturbidimetry
Suspension of uniform polystyrene latex particles coated with anti-CRP antibody
Turbidity measured at 571nm

Question 2

Procalcitonin method in your lab

Answer 2

BioMerieux Vidas 3
Fluorescence immunoassay

Question 3

What is procalcitonin?

Answer 3

The prohormone of calcitonin

Question 4

Where is procalcitonin produced?

Answer 4

By many cell types throughout the body, in response to proinflammatory stimulation, especially bacterial

Question 5

Indications for procalcitonin

Answer 5

Differentiation between bacterial infection and other causes of inflammatory reactions (viral, allergic, autoimmune, graft rejection)
RCT evidence for using PCT to guide the initiation and duration of antibiotics for LRTI in community, sepsis in ICU settings and ED

Question 6

Apart from bacterial infection, when can procalcitonin be elevated?

Answer 6

Newborns
Polytrauma
Burns
Major surgery
Prolonged/severe cardiogenic shock

Question 7

Assay principle for procalcitonin in your lab

Answer 7

One-step
Enzyme immunoassay sandwich with fluorescent detection (ELFA)
1. Sample is mixed with detection antibody with alkaline phosphatase conjugate in a well
2. Mixture is cycled in and out of a pipette (“solid phase receptacle”) lined with capture antibody
3. Unbound sample is washed away
4. Reagent - 4 methyl umbelliferyl phosphate - is cycled in and out of solid phase receptacle
5. Alkaline phosphatase catalyses the hydrolysis of 4 methyl umbelliferyl phosphate to 4 methyl umbelliferone, which is fluorescent
6. Fluorescent signal from 4 methyl umbelliferone is proportional to procalcitonin concentration

Question 8

Half-life of procalcitonin?

Answer 8

24 hours ie daily reduction in PCT by 50% is expected as sepsis resolves

Question 9

Interferences with procalcitonin assay

Answer 9

Powder from gloves
EDTA causes a falsely low result
Variation between sample type (serum and plasma) - use the same tube type for serial results
Human anti-animal antibodies and heterophile antibodies

Question 10

Are procalcitonin assays standardised?

Answer 10

No

Question 11

General interpretation of procalcitonin results?

Answer 11

<0.1ng/mL absence of bacterial infection
0.1-0.25ng/mL bacterial infection unlikely; antibiotics discouraged but if strong suspicion of sepsis remains, remeasure 6-24 hours later
0.25-0.5ng/mL - possible bacterial infection and antibiotics recommended
Greater than 0.50 ng/mL suggestive of bacterial infection and antibiotic therapy strongly recommended, remeasure 6-24 hours later
>2ng/mL - high risk for progression to severe sepsis

Question 12

What is CRP?

Answer 12

A protein which binds the cell wall C-polysaccharide of Step pneumoniae
Participates in nonspecific host defense by activating the classical complement pathway.
One of the strongest acute phase reactants