Kiss et al developed an algorithm for when to evaluate a patient with microcytosis for thalassemia. This model incorporates use of a Bayesian model based on the prevalence of beta-thalassemia in different populations. The authors are Toronto and Hamilton in Canada.
|
MCV range in femtoliters |
Positive Likelihood Ratio for beta-Thalassemia |
|
55.0 – 59.9 |
54.19 |
|
60.0 – 64.9 |
18.79 |
|
65.0 – 69.9 |
3.61 |
|
70.0 – 74.9 |
0.34 |
|
75.0 – 79.9 |
0.09 |
|
Population |
Prevalence of beta-Thalassemia |
|
African American |
1.4% |
|
Algeria |
3.0% |
|
Bulgaria, Northern |
0.1% |
|
Bulgeria, Southern |
9.0% |
|
China, Canton Area |
2.0% |
|
Crete |
7.0% |
|
Cyprus |
15.0% |
|
Ghana |
1.5% |
|
Greece, Arta District |
10.0% |
|
Greece, Mainland |
7.0% |
|
India, Ahom |
1.0% |
|
India, Assam |
5.0% |
|
India, Bangalen |
3.7% |
|
India, Bhanishali |
15.0% |
|
India, Lohana |
13.6% |
|
India, Saraswat Northwest |
4.4% |
|
India, Saraswat West |
3.5% |
|
India, Sindhi near Bombay |
8.0% |
|
Italy, Central |
1.3% |
|
Italy, Northern |
1.3% |
|
Italy, Po delta |
13.0% |
|
Italy, Southern |
10.0% |
|
Kurdish Jewish population |
20.0% |
|
Lebanon |
4.0% |
|
Liberia |
9.0% |
|
Malta |
3.5% |
|
Nigeria |
0.8% |
|
Pacific Islands, Lower Range |
2.0% |
|
Pacific Islands, Upper Range |
20.0% |
|
Pakistan, Karachi |
1.5% |
|
Pakistan, Patham |
4.0% |
|
Rhodes |
25.0% |
|
Sardinia, NOS |
12.6% |
|
Sardinia, Southern |
28.5% |
|
Sicily |
10.0% |
|
Thailand, Northern |
10.0% |
|
Thailand, NOS |
4.8% |
|
Turkey, Southwest |
1.7% |
modified after Table 4, page 1321
where:
• NOS = not otherwise specified
pre-test odds =
= (pretest probability) / (1 – (pretest probability))
posttest odds =
= (pretest odds) * (positive likelihood ratio)
posttest probability =
= (posttest odds) / (1 + (posttest odds))
Algorithm (after Figure page 1322)
If a person has an MCV < 80 fL, then calculate the post-test probability for beta-thalassemia.
When to perform a thalassemia investigation:
(1) If the post-test probability for beta-thalassemia is >= 20%.
(2) If the post-test probability for beta-thalassemia is < 20% and the serum ferritin level is normal or increased.
(2) If the post-test probability for beta-thalassemia is < 20%, the serum ferritin level is initially decreased, and the microcytosis persists after iron repletion.
Thalassemia investigation:
(1) quantitation of hemoglobins A2 and F
(2) hemoglobin electropheresis
(3) hemoglobin H inclusion body screen
(4) serum ferritin level
If the thalassemia investigation and iron deficiency workup are negative, then investigate other causes of microcytosis.
If the thalassemia investigation is positive and pregnancy is an issue, then offer genetic counseling.
Purpose: To evaluate a patient with microcytosis for thalassemia using the algorithm of Kiss et al.
Specialty: Hematology Oncology, Clinical Laboratory, Genetics
Objective: clinical diagnosis, including family history for genetics
ICD-10: D50, D56,
