To clarify potential relationships between chief complaints of patients and laboratory data with a focus on aging-related changes, we retrospectively analyzed the data of 843 patients who visited a general medicine department for the first time. Their chief complaints were classified into 8 major symptoms: visceral pain, somatic pain, fever, cough, dizziness, fatigue, appetite loss, and edema. We compared the laboratory data obtained from the patients with complaints with the data of symptom-free (control) patients. The serum sodium and potassium levels in the fever group were decreased compared to those in the control group. In the fever group, the serum sodium level was inversely correlated with age. The ratio of serum urea nitrogen to creatinine (UN/Cr) was increased in the appetite-loss group. There were significant age-dependent increases in the UN/Cr ratio in the appetite-loss and edema groups. Of note, serum levels of free thyroxin were lower in the dizziness group compared to the control group. In addition, the free thyroxin level was inversely correlated with age in the dizziness group but not in the asymptomatic control group. Collectively, the results indicated that osmolality-related laboratory data are strongly associated with individual primary symptoms at the first visit regardless of the final diagnosis. The consideration of age-dependent changes of these markers is helpful for diagnosing latent disorders based on various primary symptoms.