Differential diagnosis of anisocytosis ( size variation) and poikilocytosis ( irregular shape) are : 
-paroxysmal nightly hemoglobinuria
-thalassemia
-elliptocytosis
-spherocytosis
-myelopathy 
-folic acid deficiency anemia
-pernicious anemia
-iron deficiency anemia
-sideroblastic anemia 

Differential diagnosis of acanthocytes are : 
-chronic liver disease
-hepatic cirrhosis 
-infantile pyknocytosis 
-acanthocytosis
-uremia
-pyruvate kinase deficiency 
​-hemolytic anemia 

Differential diagnosis of ovulatory bleeding are : 
-trauma
-mid cycle ovulatory bleeding 
-prostaglandin abnormalities
-coagulation defect
-IUD ( foreign bodies) 
-endometritis
-sarcoma
-adenocarcinoma
-adenomyosis
-leiomyoma
-fibroid
-endometrial hyperplasia
-polyps
-mid cycle ovulatory bleeding 
-luteal phase dysfunction 

Differential diagnosis of anovulatory bleeding are : 
-liver disease
-exercise
-kidney disease
-weight loss 
-stress 
-thalamic lesion 
-pituitary lesion 
-peri menopausal ( disturbance of the hormonal mechanism during menopausal transition ) 
-drugs which affect the hypothalamic pituitary gonadal axis
-dysfunctional hypothalamic pituitary gonadal axis
-elevated prolactin level 
-thyroid dysfunction 
-polycystic ovarian syndrome 
-unopposed estrogen 
-not enough progesterone 

Differential diagnosis of autoimmune disorders causing severe abdominal pain are : 
-Crohn's Disease
-ulcerative colitis
-Henoch - Schonlein allergic vasculitis
​-regional enteritis 

Differential diagnosis of severe abdominal pain are : 
-chronic pancreatitis
-necrotizing hemorrhagic pancreatitis
-acute pancreatitis
-granulomatous inflammatory disorder
-toxic megacolon 
-colonic diverticulitis
-ruptured appendix
-puerperal infection 
-neoplastic disorder
-pelvic inflammatory disease
-acute peritonitis
-mesenteric adenitis
-acute cholecystitis
-recurrent acute appendicitis
-acute pyelonephritis
-acute gastroenteritis
​-twisted infarcted uterine fibroid 

Differential diagnosis of vascular disorders causing severe abdominal pain are : 
-liver infarction
-gastric infarct
-mesenteric vein thrombosis
-mesenteric infarct
-mesenteric artery occlusion 
-renal infarction 
-ruptured of aortic aneurysm 
-splenic infarction 
-hepatic ischemia
-shock liver 
-mesenteric vascular insufficiency 

Differential diagnosis of poisoning causing severe abdominal pain are : 
-food poisoning 
-arsenic poisoning 
-Zieve's Syndrome 
-lead poisoning 
-intestinal poisoning 
-Black Widow Spider Bite
-children lead poisoning 
-Clostridium perfringens
-Bacillus cereus 

Differential diagnosis of endocrinological disorders causing severe abdominal pain are : 
-adrenocorticoid deficiency 
-Addison's disease
-chronic adrenal insufficiency 
-Mittelschmerz ovulation pain 

Differential diagnosis of anatomical or structural disorders causing severe abdominal pain are : 
-placenta abruptio
-urolithiasis
-kidney stones
-nephrolithiasis
-biliary colic 
-cholelithiasis
-choledocholithiasis
-gastroduodenal perforation 
-ectopic pregnancy 
-large bowel obstruction 
-intestinal bowel obstruction 
-incarcerated hernia
-irreducible hernia
-hemoperitoneum 
-mesentery hemorrhage
-perforated duodenal ulcer
-penetrating duodenal ulcer
-renal tract
-perforation gastrointestinal tract
-bile peritonitis
-small bowel obstruction 
-cecum volvulus
-perforated cecum 
-intra abdominal hernia
-sigmoid volvulus
-intussusception 
perforation of intestine
-perforated viscus
-retro peritoneal hemorrhage