Hematology consults

For residents · Rotation prep

Benign hematology consults are detective work. The answer is usually in the trend, the smear and the medication list. Your job is to gather those three things before anyone asks.

Before you see the patient

Know the question. Call the primary team if the consult just says “anemia” or “low platelets.” What exactly do they want: a diagnosis, a transfusion decision, clearance for a procedure, anticoagulation advice?
Trend every CBC you can find, including outpatient values. When did it start, and how fast is it moving?
Read the full medication list, including heparin flushes, antibiotics, anticonvulsants and anything started in the last few weeks.
Check transfusions: what, when and how the counts responded.
Look at the smear yourself. Ask the fellow or hematopathologist to review it with you on your first day. Schistocytes, blasts, spherocytes and platelet clumps change management immediately.

Anemia

Start with the MCV and the reticulocyte count. Is the marrow responding (hemolysis, bleeding) or not (production problem)?
Iron studies: ferritin, iron, TIBC and transferrin saturation. Ferritin rises with inflammation, so a “normal” ferritin does not rule out iron deficiency in a sick inpatient.
B12 and folate. Consider methylmalonic acid when B12 is borderline.
Hemolysis labs: LDH, haptoglobin, indirect bilirubin, reticulocytes and the direct antiglobulin test (DAT, Coombs).
Send diagnostic labs before transfusing whenever you safely can. Transfused cells muddy iron studies, hemolysis labs and the smear.
Know the restrictive transfusion threshold your institution uses (usually hemoglobin 7 g/dL for most stable inpatients, sometimes higher in cardiac disease).

Thrombocytopenia

Confirm it’s real. Clumping causes pseudothrombocytopenia; repeat in a citrate tube.
Timing tells the story. A drop 5 to 10 days after heparin exposure is classic for HIT. A drop with fever and sepsis suggests consumption or marrow suppression.
HIT: calculate the 4Ts score. If intermediate or high probability, stop all heparin (including flushes and heparin-coated lines), start a non-heparin anticoagulant, and send a PF4 antibody test. Do not routinely transfuse platelets.
TTP: thrombocytopenia plus microangiopathic hemolytic anemia with schistocytes. Calculate the PLASMIC score, send ADAMTS13 before plasma exchange starts, and call your attending right away. This is an emergency. Avoid platelet transfusion unless there is life-threatening bleeding.
DIC: low platelets, prolonged PT, low fibrinogen, high D-dimer. Treat the underlying cause; replace products for bleeding or before procedures.
ITP: a diagnosis of exclusion. Treatment is generally considered for platelets under 30,000 or for bleeding.
Know the common platelet thresholds for procedures at your institution (lumbar puncture, central lines, neuraxial anesthesia).

Abnormal coagulation tests

Isolated prolonged PT: vitamin K deficiency, liver disease, warfarin, factor VII deficiency.
Isolated prolonged PTT: heparin contamination, factor deficiency, an inhibitor or a lupus anticoagulant. A mixing study separates deficiency (corrects) from inhibitor (does not correct).
Both prolonged: DIC, liver disease, severe vitamin K deficiency, supratherapeutic anticoagulation.

Thrombosis and anticoagulation

Classify the clot: provoked or unprovoked, cancer associated or not, and what the bleeding risk is.
Choose the drug with the whole patient in mind: renal function, weight, drug interactions, platelet count, upcoming procedures, cost and adherence.
Know the reversal agents: vitamin K plus 4-factor PCC for warfarin, idarucizumab for dabigatran, andexanet alfa or 4-factor PCC for factor Xa inhibitors, protamine for heparin.
Thrombophilia testing rarely changes inpatient management and many tests are unreliable during an acute clot or on anticoagulation. Ask before you send it.
Perioperative questions: when to hold, whether bridging is needed (usually not with DOACs), and when to restart.

Can’t miss: blasts on a smear. Check DIC labs, tumor lysis labs and for signs of leukostasis, and call your attending immediately. If acute promyelocytic leukemia (APL) is suspected, the treatment (ATRA) is started on suspicion, before confirmation, and the coagulopathy is corrected aggressively. Early APL deaths come from bleeding.

Other common consults

Sickle cell disease: pain crisis, acute chest syndrome, stroke. Know when simple versus exchange transfusion is indicated and keep hemoglobin targets in mind to avoid hyperviscosity.
Leukocytosis: separate reactive causes from a myeloproliferative process or leukemia. The smear and the differential matter more than the absolute count.
Erythrocytosis, thrombocytosis, eosinophilia, monoclonal proteins: know the basic secondary causes to rule out first.

Our board notes on benign hematology go deeper on each of these.