Harvey Chapter 4 Evaluation of Erythrocytes PART II AKG Flashcards
Erythrocyte and Iron Assays Ddx of anemia and erythrocytosis
What causes splenic contraction in cats, dogs, hot-blooded horses, and some marine diving mammals (e.g., seals)?
- Exercise
- Hypoxia
- Hemorrhage
- Excitement
HCT in the spleen (about 80-90%) is much higher than that of peripheral blood. T/F
True
That is why splenic contraction increases HCT 1.3-1.5x above resting levels
What causes splenic enlargement and subsequent decrease in HCT?
Anesthesia (especially with barbiturates)
Why are manual reticulocyte counts recommended to be performed in cats compared to dogs?
Cats have more punctate reticulocytes than aggregate reticulocytes. In dogs, aggregate reticulocytes are present in blood for a few days and mature into punctate reticulocytes for only a very short period of time (hours?) before they become mature RBCs. In cats, punctate reticulocytes circulate in blood for up to a week before they mature. Additionally, punctate reticulocytes continue to be released from BM after HCT begins to increase and aggregate reticulcoyte release has ceased in cats. Most analyzers do not detect punctate reticulocytes because of the very small amount of ribosomal DNA present, and manual counts are required to count both aggregate and punctate reticulocytes.
What is the corrected reticulocyte count equation?
(patient’s HCT/mean normal HCT) x raw reticulocyte count%
How long does it take to reach a maximal aggregate reticulocyte response to anemia?
4 days
What are these larger cells?
Macroreticulocytes (aka ‘stress’ reticulocytes) - thought to occur during severe regenerative anemia - thought that one less mitotic division occurs during production and that large immature reticulocytes are released
The MCV is larger in the fetus or adult?
What it is compared to adults at the time of birth in dogs and cats vs horses and cattle?
Fetus
Horses and catte at birth: MCV is within adult RI
Cats and dogs at birth: MCV is higher than adult RI
Copper and pyridoxine are important in iron metabolism and heme synthesis. Deficiencies in these nutrients may result in _____ anemia.
microcytic
Which drugs interfere with heme synthesis and have the potential for causing the formation of microcytic RBCs with siderotic inclusions?
- chloramphenicol
- lead
- hydroxyzine in dogs
Which dog breeds normally have MCV values below the reference interfals established for other breeds of dogs, but they are not anemic?
Japanese breeds: akita and shiba
MCVs may be spuriously ______ in dogs with persistent hyponatremia.
MCVs may be spuriously ____ and MCHC may be spuriously ______ in dogs with persistent hypernatremia.
MCVs may be spuriously decreased in dogs with persistent hyponatremia because RBCs shrink when they are diluted in vitro with counting fluid. MCVs may be spuriously increased and MCHC may be spuriously decreased in dogs with persistent hypernatremia because RBCs swell when they are diluted in vitro.
What causes high MCHC values?
- Artifactual increases in hemoglobin: lipemia, protein precipitation (cryoprotins and paraproteins), Heinz bodies
- Artifactual decreases in HCT (via analyzer): in vitro or in vivo hemolysis, RBC agglutination
*remember MCHC = Hgb/HCT x 100
In iron deficiency, which value decreaes first:
MCV or MCHC?
MCV first, then MCHC
What would cause two separate populations like this on the histogram?
Blood transfusion of a donor that has a substantially different MCV.
May also see two populations if there is substantial fragmentation of RBCs
You have normal or increased PaO2 but arterial blood is dark-colored. What should you suspect?
Methemoglobinemia
Significant methemoglobinemia (oxidative damage) has been associated with clinical cases of which toxins (that serve as oxidants)?
- Benzocaine
- Acetominophen
- Phenazopyridine in cats
- Skunk musk in dogs
- Chlorate toxicity in cattle
- Copper toxicity in sheep and goats
- Red maple toxicity in horses and alpacas
- Nitrite (cattle eating nitrate-accumulating plants and nitrate is reduced to nitrite by ruminal microbes) - also sodium nitrite preservative
- Onions/garlic
- Naphthalene (moth repellent) in dogs
- Methylene blue in cats
- Propofol and propylene glycol in cats
- Brassica sp. (kale) in cows
Persistent methemoglobinemia resulting from RBC ______ deficiency has been recognized in many dog breeds, DSH cats, and horses.
Cytochrome B5 reductase
*animals with this deficiency, in contrast to thsoe with methemoglobinemia produced by oxidant drugs, usually exhibit few or no clinical signs of illness
Which anticoagulant causes erroneuously low iron concentrations when measuring serum/plasma iron concentrations?
EDTA
so use heparin or serum
Serum iron concentration is generally increased (hyperferremia) in animals with….
- Hemolytic anemia
- Dyserythropoiesis
- Hypoplastic or aplastic anemia
- Iron overload
- Acute iron toxicity
- Chronic hepatopathy (dogs)/acute hepatocellular necrosis
- Experimental pyridoxine deficiency (pigs)
- Administration of glucocorticoids (dogs and horses)
- Opposite effect in cattle and goats
Serum iron concentration is low in….
- Iron deficiency anemia
- Inflammation
- ~50% of dogs with PSS
- Demand for iron > iron stores: EPO administration or acute hemorrhage
- GC administration in cattle and goats (opposite in dogs and horses)
How can serum ferritin concentrations help differentiate true iron deficiency from anemia of inflammatory disease?
Because both conditions will have decreased circulating serum iron levels, but only true iron deficiency will have decreased serum ferritin. Serum ferritin will be normal to high in anemia of inflammation.
What increases serum ferritin concentrations?
- Hemolytic anemia
- Inflammation (ferritin is an APP)
- Liver damage: toxic, hepatitis
- Malignancy: HS, LSA in dogs
- Iron overload
- Transiently increased in horses after moderate to severe exercise and in foals following consumption of colostrum
Stainable iron is assessed int he bonw marrow with which stain?
Prussian blue
Identify which parameters will increase and which will decrease to aid detecting early iron deficiency in dogs.
- CHr
- MCVr
- CHCMr
- %LowCHr
- %Hypo-r
- CHr ↓
- MCVr ↓
- CHCMr ↓
- %LowCHr ↑
- %Hypo-r ↑
*%LowCHr = percentage of all reticulocytes with low hemoglobin (a preset value)
*CHr = mean hemoglobin concentration in reticulocytes
*These changes are not specific for iron deficiency, but should raise supsicion for iron deficiency
____ is considered as an indirect measure of transferrin concentration in serum or plasma.
total iron binding capacity (TIBC)
What causes a decrease in TIBC?
- Decreased production:
- Increased hepatocyte iron content
- Inflammation (transferrin is a negative acute phase protein)
- Hepatic insufficiency or PSS
- Decreased protein intake
- Loss
- Lost with albumin in PLN or PLE or exudative disorders
- Catabolism during negative energy balance
What causes increases in TIBC?
- Iron deficiency (woodchucks, pigs, horses, and cattle; not so much in dogs, cats or camelids)
- Artifact: high serum iron (e.g., iron overload), and possibly severe lipemia
- Necrotizing hepatitis in dogs (mechanisms unclear)
How is TIBC measured?
- Add a known amount of iron – some of these iron molecules will bind to unsaturated transferrin, and the rest will remain free
- Measure excess free iron in alkaline pH
- Total Fe added – excess free Fe = UIBC (amount of unbound iron sites on transferrin)
- UIBC + serum Fe = TIBC
How is iron measured?
Approximately ____ of the circulating iron binding sites on transferrin are occupied in healthy patients.
33%
Calculate the % saturation (Tf)
% saturation of Tf = [iron/TIBC] x 100
Interpret:
Iron ↓
TIBC normal
% saturation ↓
Any cause of low iron. Most common causes are transient variation and inflammatory disease. May be seen with or without anemia. If there is a concurrent anemia, these results do not indicate an iron deficiency anemia (would expect low TIBC), unless there is evidence of chronic external blood loss and concurrent expected changes in hemogram results (microcytic hypochromic RBC indices).
Interpret:
Iron ↓
TIBC ↓
% saturation N
ferritin - N to ↑
This pattern is typical of inflammation of >24-48 hours duration. Both iron (inflammatory cytokines, hepcidin) and TIBC (negative acute phase protein) decrease, resulting in a normal % saturation.
Interpret:
Iron - N
TIBC - ↓
% saturation - N, ↑
Loss or decreased production of transferrin, e.g. protein-losing enteropathy
Interpret:
Iron - ↑
TIBC - N
% saturation - ↑
ferritin - ↑
- Hemolytic anemia
- Non-regenerative IMHA (PIMA) or pure red cell aplasia
Hereditary stomatocytosis
Breeds
Clinicopathologic findings
Where is the defect
- Breeds: dwarf Alaskan Malamute dogs, Drentsche Patrijshond, standard and mini schnauzers
- C/S: Macrocytic, hypochromic RBCs; HCTs are often within normal range due to larger RBC size; ↓ RBC life span (EVH - osmotically and mechanically fragile); reticulocytosis
- Defect: Membrane defect involving increased Na and water influx - abnormal phospholipid composition in RBC membrane (increased sphingomyelin and decreased cholesterol and phosphatidylcholine)
Which animals can normally have stomatocytes?
Woodchucks
Manatees
Dolphins
Hemolytic anemia can be caused by decreases in this analyte, which can commonly decrease secondary to postparturient hemoglobinuria (cattle), ketoacidotic diabetic animals following insulin therapy (cats and dogs), hepatic lipidosis (cats)
Hypophosphatemia
*can be lost in milk in cattle; insuline promotes movement of glucose and phosphate into cells other than RBCs (remember glucose transport into RBCs is NOT insulin dependent)
*bilirubin interference can cause artifactual hyposphatemia
List ddx for macrotyic hypochromic anemia
- Regenerative anemia with marked reticulocytosis
- Hereditary stomatocytosis in dogs
- Abyssinian and Somali cats with increased erythrocyte osmotic fragility
- Spurious with prolonged storage of blood sample