High rates of repeated blood sampling are putting patients in haematology/oncology units at risk of iatrogenic anaemia, a new report suggests.

A 2019 blood sampling audit carried out in hospitals in four states and territories found that some units such as ICU and haematology/oncology had high cumulative volume of blood samples taken from patients that could put them at risk of anaemia and potentially the need for blood transfusion.

The audit was conducted to assess responses to minimal blood sampling recommendations made after concerns were raised in 2017 that phlebotomy volumes of around 60 mL per day in patients could lead to high cumulative blood loss and so-called ‘hospital-acquired anaemia.

Nearly 4,000 samples were assessed from 550 patients on medical wards (n = 7), haematology/oncology units (n = 5), ICU/HDU (n = 15), and NICU (n = 2), representing 20% of health services.

The audit found that the average number of blood draws per day ranged from 0.5 on medical wards to as many as 3.6/day on some ICUs, with haematology units having an average of 0.8-1.1 draws per day.

The average volume of blood drawn per patient per day varied significantly between units, from an average of 5 mL (range 0.8-15ml) on medical wards to as much as 33 mL (range 2 -111 mL) on an ICU. For one group of haematology/oncology units the average draw was 19ml (range 0.5-66 mL) per patient per day.

After adjusting for length of stay, the cumulative phlebotomy volume was as high as 100ml (range 2.7-463 mL) from some haematology/oncology units, compared to around 20-28 mL per patient for medical wards, and 121 mL for some ICU.

The audit found that some line clearance discard was occurring and unavoidable in ICU patients with about 50% of the total blood drawn (16 mL/day) lost. Blood was also discarded due to drawing more than required, with the average amount discarded in haematology/oncology unit patients being as much as 7.0ml per patient per day (range 0.9–16.1 mL).

The majority of blood sampling (69%) occurred due to routine blood orders, rather than by clinical review and subsequent medical request (26%)

Since every 1 mL of phlebotomy in adults would result in decrease in haemoglobin of 0.07 g/L, the cumulative phlebotomy volumes were estimated to result in a drop in haemoglobin of 7.0 g/L (range 0.2–32.4) for haematology/oncology patients and 8.5 g/L (range 0.3–50.4) for ICU patients.

The report authors concluded that “there is potential concern for iatrogenic anaemia developing in patients in … ICU and haem/onc patients based on cumulative blood sampling volumes over the study length of stay. The large volumes were due to a combination of longer length of stay, more frequent testing and higher rates of line clearance.”

“Overall, there was no apparent improvement in policy promoting minimal blood sampling practices,” they noted.

They repeated their recommendations that individual healthcare services should review their practices on routine orders blood sampling and implement patient blood management (PBM) policies such as use of use of small volume sample tubes.

“Health services should consider including audit of cumulative daily phlebotomy loss per patient as a Blood Management/Hospital Transfusion Committee agenda item to review and make recommendations around practice to address potential iatrogenic anaemia,” they suggested.