Setting: office
CC: “My urine is dark when I get up in the morning.”
VS: R: 24 breaths/minute; BP: 110/70 mm Hg; P: 78 beats/minutes; T: 97.8°F
HPI: A 24-year-old man with intermittent episodes of dark urine in the morning comes to your office. He has been feeling “weak and tired” for months. He gets short of breath when he is walking up stairs and is easily fatigued. He does not have a fever and has not had any infections in the past.
PMHX: deep venous thrombosis (DVT) of portal vein 2 years ago treated with 6 months of warfarin
Medications: none
PE:
General: pale and tired, yellow tone to sclerae
Cardiovascular: 1/6 systolic murmur
Extremities: no edema, no tenderness
Neurological: normal
Initial Orders:
CBC
UA
CHEM-7
LFTs
What is the most common cause of hematuria?
a. Infection
b. Stones
c. Trauma
d. Neoplasia
Answer a. Infection
By far, the most common cause of dark urine from hematuria is infection, although dysuria (frequency, urgency, burning) should also be present and is not in this patient. Renal and bladder stones can certainly be the cause, but would usually be accompanied by flank pain. Although 2% to 5% of patients with renal cell cancer have polycythemia from excess erythropoietin production, it is far more common for renal cancer to present with hematuria and anemia.
There is no point in discussing dark urine without first excluding infection.
Move the clock forward only 1 to 2 days. Even though the test results may come back in just 2 to 4 hours if ordered “Routine,” do not keep a patient waiting for hours in the office for these test results. Have the patient go home and come back to receive the results.
Reports:
CBC: hematocrit 28%; WBCs 2,800/μL (low); platelets 94,000/μL (low)
UA: dipstick positive for hemoglobin, no urobilinogen; no WBCs
CHEM-7: potassium (K) 5.3 mEq/L; otherwise normal
LFTs: indirect bilirubin 4.2 mg/dL (elevated); LDH elevated
Rapid hemolysis causes hyperkalemia.
Intravascular hemolysis gives hemoglobin in urine, with no RBCs.
Orders:
Peripheral smear
Reticulocyte count
Haptoglobin level
Coombs test
Have the patient return the following day to discuss laboratory test results:
Smear: schistocytes, fragmented cells
Reticulocytes: 14%
Haptoglobin: decreased
Coombs test: negative
Haptoglobin binds and transports newly released hemoglobin from destroyed RBCs to spleen and liver for recycling.
Free Hb and iron are damaging to the kidneys. Haptoglobin grabs it before it “burns” the kidney.
Hb is oxidized in the kidney to hemosiderin.
What is the mechanism of renal damage from hemoglobin?
a. Glomerulonephritis
b. Nephrotic syndrome
c. Acute tubular necrosis
d. Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
e. Obstruction
Answer c. Acute tubular necrosis
When haptoglobin is used up, free hemoglobin filters in the kidney and oxidizes the tubules potentially leading to renal failure from acute tubular necrosis (ATN). Hemosiderin in the urine is an indication of this severe oxidative toxicity to the kidney. Cells in the tubules and macrophages pick up discarded iron and store it in tissue as hemosiderin. When seen on UA, hemosiderin is a bad thing. It means enough free iron and hemoglobin have been released to overwhelm the haptoglobin, and now the macrophages are grabbing it to store it in tubule cells. The tubule cells then die, slough off, and end up in the patient’s urine as hemosiderin.
Steps in Hemosiderin Production and Renal Injury
1. Macrophages scavenge
bad iron.
2. Macrophages make hemosiderin in tissue.
3. Hemosiderin “cooks” the tubule cells.
4. Dead cells fall into the urine.
Hemosiderin in Urine = Zombie Tubule Cells
On the Step 3 examination, prognosis questions are often asked. They are phrased as: “What can the patient expect?”
The patient has hemolysis with pancytopenia. The presence of schistocytes and fragmented cells indicates intravascular hemolysis. The Coombs test is negative. Haptoglobin is more likely to be low in intravascular hemolysis. There is the DVT in an unusual site.
Pancytopenia + Intravascular Hemolysis + Clots = PNH
What is the most accurate test to establish a diagnosis of PNH?
a. Sugar water (sucrose hemolysis) test
b. CD55 and CD59 by flow cytometry
c. Ham test
d. Complement levels
Answer b. CD55 and CD59 by flow cytometry
CD55 and CD59 are the markers for complement-removing proteins indicating the deficiency of glycosylphosphatidylinositol (GPI), a protein that characterizes PNH. Normally, complement attaches to cells, but is removed by certain proteins before they are able to destroy the RBC. These proteins act as complement-removing factors and are sometimes called decay-accelerating factors. They anchor to the RBC on GPI. PNH is a genetic defect in GPI. The complement-removing proteins do not attach. Cells are then destroyed by complement.
The mutation-damaging GPI is on the stem cell.
PNH Stem Cell Defect = Pancytopenia
Which of these is not in the prognosis of PNH?
a. Iron deficiency anemia
b. Myelodysplasia
c. Polycythemia vera
d. Recurrent DVT
e. Acute myeloid leukemia
Answer c. Polycythemia vera
As a clonal stem cell defect, PNH can transform into a number of hematologic malignancies, such as acute leukemia. Aplastic anemia and myelodysplasia are routine findings. The only way to cure PNH, therefore, is with a bone marrow transplant to remove the underlying stem cell defect. Because of the morbidity and mortality associated with the bone marrow transplant procedure, treatment with chronic transfusion and iron replacement is often preferred.
The only way to cure PNH is bone marrow transplantation.
What is the original root cause defect of PNH?
a. The mutation is in the phosphatidylinositol glycan anchor biosynthesis, class A (PIGA) gene.
b. There is a failure to produce the anchoring protein, GPI.
c. Decay-accelerating factor (DAF) or CD55 and CD59 cannot attach.
d. The complement stays attached to the RBCs.
e. RBCs are destroyed.
Answer a. The mutation is in the phosphatidylinositol glycan anchor biosynthesis, class A (PIGA) gene.
The sequence of events in PNH starts with choice a (PIGA is defective). Without PIGA, the GPI anchor is not made. Without the GPI anchor, DAF and CD59 do not attach to the RBC membrane. Without DAF and CD59, the complement stays attached and destroys cells. The root cause of everything, however, is the defect or mutation in the PIGA gene (Figure 2-6).
Figure 2-6. The complement cascade and the fate of red blood cells (RBCs). A. Normal red blood cells are protected from complement activation and subsequent hemolysis by CD55 and CD59. These two proteins, being glycosylphosphatidylinositol (GPI)-linked, are missing from the surface of paroxysmal nocturnal hemoglobinuria (PNH) red blood cells as a result of a somatic mutation of the X-linked PIGA gene that encodes a protein required for an early step of the GPI molecule biosynthesis.
B. In the steady state, PNH erythrocytes suffer from spontaneous (tick-over) complement activation, with consequent intravascular hemolysis through formation of the membrane attack complex (MAC); when extra complement is activated through the classical pathway, an exacerbation of hemolysis will result. (Reproduced with permission from Luzzato L, et al. Paroxysmal nocturnal hemoglobinuria and eculizumab. Haematologica 210;95(4):523−526.)
Why is there more hemolysis at night?
Lower respiratory rate increases the partial pressure of carbon dioxide (PCO2), which makes slight acidosis, in turn, activating more complement.
The patient’s low cytometry shows a deficiency of CD55 and CD59. You get the message, “This case will end in 5 minutes of real time.” Your final orders should be:
Supplement with iron and folic acid.
Transfuse as needed.
Give steroids when the transfusion requirement is large.
Give eculizumab to decrease transfusion dependence.
Eculizumab is an antibody against C5 complement.
Eculizumab removes complement from RBCs.
Steroids may diminish complement activation.