To answer the question whether a non-invasive haemaglobin measurement is clinically useful, reliable and accurate as compared to taking a blood sample and checking the haemaglobin level at the laboratory or in a blood gas analyser. This study will take place in a multi-disciplinary ICU of critically ill patients.

A presenting sample of 150 patients requiring admission to ICU will be enrolled. These will include paediatric, trauma, adult medical and adult surgical patients. Informed consent will be obtained. Baseline demographic data, vital signs, Massey pigmentation score, and severity of illness scores will be calculated, as well as finger deformity, if present, nail polish or acrylics, smoking habits, finger diameter of finger measured, comorbidities and medications. Patients will be admitted in the usual way, and admission bloods will be sent to the laboratory as per usual protocol. Enrolled patients will in addition have their Haemaglobin and Plethysmography Index (measure of perfusion) measured non-invasively using the Masimo Pronto-7 handheld device. Note of concurrent medications, blood products and vital signs will be recorded at each measurement. Each patient will have measurements done 8 hourly (between 1-5 measurements per patient). Concurrent arterial blood gas samples will be taken in a heparinised syringe and performed on ABL radiometer blood gas analyser.. An additional EDTA blood sample shall be taken at each Pronto measuring point which will be measured at the laboratory on a Sysmex cell counter. Analysis of data will assess precision and accuracy, trend accuracy, and effect of pigmentation, vasopressors and other medication on the results of the non-invasive co-oximetry estimation of haemaglobin.

Inclusion Criteria:

• All patients with a condition that requires admission to ICU shall be considered to be eligible.
• Age 1month to 100years old

Exclusion Criteria:

• Patients under 1 month old
• Patients with an unrecordable blood pressure or body temperature <34 degrees.