Osteoarthritis (OA) with Crystal Arthropathy: Given the patient's age and the sudden onset of non-traumatic knee effusion, OA with a possible crystal arthropathy (though urate levels are normal, other crystals like calcium pyrophosphate dihydrate could be considered) is a strong consideration. The absence of significant inflammatory markers (negative CRP) and the presence of anti-CCP (which can be positive in OA) support this diagnosis.

Psoriatic Arthritis (PsA): Although the patient is from the Philippines, where PsA might be less common than in Western populations, the presence of anti-CCP and a sudden onset of knee effusion could suggest PsA, especially if there are other signs of psoriasis or a history suggestive of psoriatic arthritis.
Seronegative Rheumatoid Arthritis: The patient has a positive anti-CCP but negative rheumatoid factor, which could still be consistent with a form of rheumatoid arthritis, particularly given the sudden onset of symptoms. However, the lack of systemic symptoms and negative CRP makes this less likely.
Lyme Arthritis: Although less common in the Philippines, travel history or exposure to endemic areas could make this a consideration, especially with sudden onset of knee effusion. However, this would typically be accompanied by other symptoms such as fever, rash, or a history of tick bite.

Septic Arthritis: Despite the lack of systemic inflammatory response (negative CRP), septic arthritis is a medical emergency that must be considered, especially in the context of a sudden onset of joint effusion. The absence of trauma does not rule out infection, and a joint aspirate is crucial for diagnosis.
Malignancy (e.g., Leukemic or Lymphomatous Arthropathy): Though rare, malignancies can present with sudden onset of joint effusion. Given the patient's age, this is a diagnosis that must be considered and ruled out, especially if other systemic symptoms are present.

Hemophilic Arthropathy: If the patient has a known bleeding disorder, hemophilic arthropathy could be considered, though this would typically present with a history of recurrent joint bleeds.
Charcot Arthropathy (Neuropathic Arthropathy): In the context of diabetes or other neuropathic conditions, Charcot arthropathy could present with sudden onset of joint effusion and destruction, though this is less common in the knee.
Amyloid Arthropathy: This is a rare condition that can present with joint effusions and is associated with amyloid deposits in the joint. It's more commonly seen in patients with chronic diseases like renal failure or multiple myeloma.