Table 3.

Laboratory investigations to consider in the diagnosis of recurrent superficial abscesses formation.

Laboratory investigation	Specific features
FBC	White cell differential − neutropenia or lymphopenia, platelet count − thrombocytopenia
Blood film	Abnormalities in neutrophil or platelet morphology and platelet size (microthrombocytopenia in WAS)
IgE	Elevated in atopic eczema, very high levels may suggest hyper-IgE syndrome
CRP	Evidence of active infection or ongoing inflammation (IBD)
Blood glucose	Diabetes confirmation
Microbiology	Staphylococcal carriage/MRSA screen, culture and PCR of lesional tissue
Histology	White cell infiltration (absence in LAD), granuloma formation (maturity thereof in MSMD)
Neutrophil function	Metabolic burst by flow cytometry (Fig. 1) or nitroblue tetrazolium reduction (NBT) test − CGD
Neutrophil phenotyping	Adhesion molecule expression by flow cytometry − LAD
Lymphocyte phenotyping	Surface expression of B, T and NK cell markers (may identify CD4 lymphopenia or HIV infection, for example)
IFN-γ/IL-12 pathway analysis	To identify patients with MSMD
Specific protein expression and genetic analysis	For specific primary immune deficiency diagnosis via specialist referral laboratory
HIV, hepatitis B and C (HCV) status	In injection drug users presenting with recurrent superficial abscesses
Renal function	Particularly in patients with diabetes and HCV infection
C4 and cryoglobulin	If cryoglobulinaemia a potential complicating factor, e.g. in HCV infection

CGD, chronic granulomatous disease; CRP, C-reactive protein; FBC, full blood count; IFN, interferon; IL, interleukin; IgE, immunoglobulin E; HIV, human immunodeficiency virus; NK, natural killer; MRSA, methicillin-resistant Staphylococcus aureus; MSMD, Mendelian susceptibility to mycobacterial disease; WAS, Wiskott–Aldrich syndrome; PCR, polymerase chain reaction; LAD, leucocyte-adhesion deficiency syndrome-1; IBD, inflammatory bowel disease.