A 5-year-old boy develops dark red urine two days after a febrile upper respiratory infection. Hemoglobin is 7 g/dL with a reticulocyte count of 0.5 percent. Direct antiglobulin test is positive for complement only. Incubation of his serum with normal RBCs causes lysis at 4 degrees Celsius and again on rewarming to 37 degrees Celsius. The responsible antibody has specificity against which antigen?

• A I antigen
• B Kell antigen
• C Rh D antigen
• D P antigen ✓

Explanation

This is paroxysmal cold hemoglobinuria. The Donath-Landsteiner antibody is an IgG biphasic hemolysin that binds the P antigen on red cells in the cold peripheral circulation, fixes complement, and then lyses the cells when they rewarm centrally. Cold agglutinin disease antibodies are IgM directed against the I or i antigen and cause chronic extravascular hemolysis rather than episodic hemoglobinuria. PCH typically follows viral infections in children and usually resolves spontaneously within weeks.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.