Relationship between abnormal laboratory results and recorded clinical diagnoses in tertiary hospital settings: a retrospective observational study

Background: The relationship between laboratory results and clinical decisions, including diagnoses, is not always clear. This study aims to determine the association between abnormal laboratory test results and diagnoses recorded by the clinicians within the electronic medical records in tertiary hospital settings. Method: We conducted a retrospective observational study using anonymised linked hospital data of 223,789 adult admissions between January 2020 and December 2021 in two Local Health Districts in New South Wales, Australia. Data extracted from hospital information systems included patient demographics, recorded clinical diagnoses and laboratory test results. We analysed correlations between abnormal results from common laboratory tests (nasopharyngeal/ oral swab SARS-CoV-2 PCR, serum/plasma total prostate-specific antigen (PSA) antigen [PSA], free thyroxine [free T4], thyroid stimulating hormone [TSH], cardiac troponin T, and cortisol) and their respective recorded diagnoses. Results: We observed the following Spearman correlation coefficients between abnormal laboratory test results and their corresponding recorded clinical diagnoses: positive SARS-CoV-2 PCR and COVID-19 (ρ=1.00), total PSA >10 µg/L and prostate cancer (ρ=0.66), free T4 >25.0 pmol/L and hyperthyroidism (ρ=0.58), TSH >5.00 mIU/L and hypothyroidism (ρ=0.56), TSH <0.30 mIU/L and hyperthyroidism (ρ=0.55), cardiac troponin T >20 ng/L and acute coronary syndrome (ρ=0.51), free T4 <8.0 pmol/L and hypothyroidism (ρ=0.42), and cortisol <80 nmol/L and adrenal insufficiency (ρ=0.33). Conclusions: This study demonstrates that abnormal laboratory results play an important but varied role in clinical diagnoses. The weaker associations highlight that laboratory tests may be utilised differently in different clinical pathways, underscoring the complex relationship between laboratory results and clinical diagnoses, and the importance of considering abnormal test results in the appropriate clinical context.