A 7-year-old boy presented with swelling, tea-colored urine, and irritability. He had a history of strep throat diagnosed 2 weeks prior and elevated antistreptolysin O titer. Urinalysis showed proteinuria and hematuria. The most likely abnormalities in serum complement levels would be low C3 and low C4 levels, consistent with post-streptococcal glomerulonephritis. A 5-year-old girl presented with respiratory distress, hemoptysis, and decreased urine output. Labs showed renal failure, hematuria, and a positive myeloperoxidase antibody. The most likely underlying pathophysiologic process is antibody-mediated neutrophil activation

1. Serological Studies
Ibrahim Sandokji

2. A 7-year-old boy is seen in the emergency department because of
swelling, tea-colored urine, and irritability. On physical examination, he
has generalized edema and a blood pressure of 129/83 mm Hg. His
other vital signs are normal. Urinalysis reveals proteinuria (2+), 10 to 20
white blood cells per high-power field, more than 100 red blood cells
per high-power field, and a urine protein to creatinine ratio of 0.9.
Serum electrolytes are normal, blood urea nitrogen level is 29 mg/dL
(10.4 mmol/L), and creatinine level is 1.1 mg/dL (97 μmol/L). He has a
history of streptococcal pharyngitis (strep throat) diagnosed 2 weeks
earlier, and the antistreptolysin O titer was significantly elevated.
Of the following, the MOST likely abnormalities in serum complement
concentrations are
A. low C3 and low C4 levels
B. low C3 and normal C4 levels
C. normal C3 and low C4 levels
D. normal C3 and normal C4 levels

3. A 5-year-old female patient presents to the
emergency department with respiratory distress
and hemoptysis for 3 days. Dark urine and
decreased urine output was noted on the day of
presentation. There are no rashes or joint pains
and review of systems is otherwise negative.
On physical examination, she is afebrile with a
blood pressure of 120/92 mm Hg, heart rate of
110 beats/min, and respiratory rate 40
breaths/min. Physical examination findings are
notable for moderate respiratory distress and
bilateral crackles on lung examination.
Urinalysis findings are notable for 300 mg/dL
protein and large blood with red blood cell
casts seen on urine microscopy.
Laboratory findings are as follows:
Sodium 141 mEq/L (141 mmol/L)
Potassium 5.6 mEq/L (5.6 mmol/L)
Chloride 101 mEq/L (101 mmol/L)
Bicarbonate 7 mEq/L (17 mmol/L)
Blood urea nitrogen 56 mg/dL (20 mmol/L)
Creatinine 3.5 mg/dL (307 μmol/L)
Glucose 118 mg/dL (6.5 mmol/L)
Calcium 8.8 mg/dL (2.2 mmol/L)
Phosphorus 6.1 mg/dL (1.9 mmol/L)
White blood cells 28,000/μL (28×109/L)
Hemoglobin 8.8 g/dL (88 g/L)
Hematocrit 28%
Platelet count 94×103/μL (94×109/L)
Peripheral blood smear Negative for schistocytes
Complement (C) 3 Normal
C4 Normal
Anti-streptolysin O Negative
Antinuclear antibodies Negative
Proteinase 3 antibody Negative
Myeloperoxidase
antibody
Positive
Anti–glomerular
basement membrane
Negative

4. Of the following, the MOST likely pathophysiologic process
underlying this child’s renal disease is
A. antibody-mediated neutrophil activation
B. anti–factor H autoantibodies
C. circulating antibody-antigen complexes
D. circulating autoantibodies against collagen type IV

5. Content Specifications

6. Let’s review the complement pathway

7. Bernabeu. Nephron 2020

8. Differential diagnosis of low C3/C4
Normal C3/C4 ↓ C3 ↓ C4 & ↓ C3
IgA/HSP PIGN Lupus
Membranous GN C3G - MPGN Ig-mediated MPGN
RPGN
MCD/FSGS
ANCA/anti-GBM

9. Cincinnati diagnostic algorithm

10. Total hemolytic (CH50) assay
 To assess both the classical and terminal pathways.
 A normal CH50 result is dependent on the presence
and functionality of both classical pathway (C1q, C4,
C2, C3) and terminal (C5, C6, C7, C8, and C9)
complement components, and is abnormally low if
any component is defective.
 Useful to monitor patients with TMA being treated
with eculizumab. Adequate dosage and dosing
interval of eculizumab should result in a total
blockade of activation of the terminal complement
pathway, and a patient’s CH50 should be at or near
0 as a result.

11. Soluble membrane attack complex (sMAC/sC5b-9)
 Eculizumab binds C5 & inhibit
its cleavage to C5a and C5b and
prevent the generation of the
terminal complement complex, C5b-
9
 sMAC is elevated in untreated or
inadequately suppressed aHUS
 Level should be normal if adequately
treated

13. Content Specifications

14. Antinuclear antibody (ANA)
 Autoantibodies against normal cell nucleus parts
 Markedly elevated in most patients with SLE
 If positive -> should be followed by more specific testing e.g. anti-dsDNA
 Lower titers (1:40 or 1:80) are non-specific and can be seen in other
inflammatory conditions
 Note: a positive ANA can be found in 30% of healthy individuals

15. ANA patterns
Diseases
Homogenous
pattern
Peripheral
Pattern
Speckled
pattern
Nucleolar
pattern
Systemic lupus erythematosus + positive + positive + positive + positive
Mixed connective disease + positive + positive
Scleroderma + positive + positive
Rheumatoid arthritis + positive
Sjogren’s syndrome + positive
Polymyositis + positive + positive

16. Content Specifications

17. Anti-neutrophil cytoplasmic antibody (ANCA)
P-ANCA (perinuclear ANCA)
Target myeloperoxidase (MPO)
C-ANCA (cytoplasmic ANCA
Target proteinase 3 (PR3)

18. ANCA-associated vasculitis
(AAV)
Microscopic
polyangiitis
pANCA
(against MPO)
Eosinophilic
granulomatosis
with polyangiitis
(Churg-Strauss
syndrome).
pANCA
(against MPO)
Granulomatosis
with polyangiitis
(Wegener
granulomatosis)
cANCA
(against PR3)

19. Content Specifications

20. Anti-glomerular basement Membrane antibody
 Anti-GBM disease is the least common but most aggressive form of
RPGN
 Circulating autoantibodies to the GBM
 IgG autoantibodies target the noncollagenous 1 (NC1) domain of the α3-chain
of type IV collagen
 Linear deposition of IgG along the basement membrane
 It may involve the kidneys alone (Goodpasture disease), or be
accompanied by pulmonary hemorrhage (Goodpasture syndrome)

21. Immunofluorescence staining showing immunoglobulin G linear staining of
the (a) glomerular and (b) alveolar basement membrane in a patient with
Goodpasture syndrome

22. A 7-year-old boy is seen in the emergency department because of
swelling, tea-colored urine, and irritability. On physical examination, he
has generalized edema and a blood pressure of 129/83 mm Hg. His
other vital signs are normal. Urinalysis reveals proteinuria (2+), 10 to 20
white blood cells per high-power field, more than 100 red blood cells
per high-power field, and a urine protein to creatinine ratio of 0.9.
Serum electrolytes are normal, blood urea nitrogen level is 29 mg/dL
(10.4 mmol/L), and creatinine level is 1.1 mg/dL (97 μmol/L). He has a
history of streptococcal pharyngitis (strep throat) diagnosed 2 weeks
earlier, and the antistreptolysin O titer was significantly elevated.
Of the following, the MOST likely abnormalities in serum complement
concentrations are
A. low C3 and low C4 levels
B. low C3 and normal C4 levels
C. normal C3 and low C4 levels
D. normal C3 and normal C4 levels

23. A 5-year-old female patient presents to the
emergency department with respiratory distress
and hemoptysis for 3 days. Dark urine and
decreased urine output was noted on the day of
presentation. There are no rashes or joint pains
and review of systems is otherwise negative.
On physical examination, she is afebrile with a
blood pressure of 120/92 mm Hg, heart rate of
110 beats/min, and respiratory rate 40
breaths/min. Physical examination findings are
notable for moderate respiratory distress and
bilateral crackles on lung examination.
Urinalysis findings are notable for 300 mg/dL
protein and large blood with red blood cell
casts seen on urine microscopy.
Laboratory findings are as follows:
Sodium 141 mEq/L (141 mmol/L)
Potassium 5.6 mEq/L (5.6 mmol/L)
Chloride 101 mEq/L (101 mmol/L)
Bicarbonate 7 mEq/L (17 mmol/L)
Blood urea nitrogen 56 mg/dL (20 mmol/L)
Creatinine 3.5 mg/dL (307 μmol/L)
Glucose 118 mg/dL (6.5 mmol/L)
Calcium 8.8 mg/dL (2.2 mmol/L)
Phosphorus 6.1 mg/dL (1.9 mmol/L)
White blood cells 28,000/μL (28×109/L)
Hemoglobin 8.8 g/dL (88 g/L)
Hematocrit 28%
Platelet count 94×103/μL (94×109/L)
Peripheral blood smear Negative for schistocytes
Complement (C) 3 Normal
C4 Normal
Anti-streptolysin O Negative
Antinuclear antibodies Negative
Proteinase 3 antibody Negative
Myeloperoxidase
antibody
Positive
Anti–glomerular
basement membrane
Negative

24. Of the following, the MOST likely pathophysiologic process
underlying this child’s renal disease is
A. antibody-mediated neutrophil activation
B. anti–factor H autoantibodies
C. circulating antibody-antigen complexes
D. circulating autoantibodies against collagen type IV

25. Thank you